Fifty&#;two studies were excluded after full text screening. Reasons for exclusion were as follows: intervention, i.e. evaluating a laser that is not currently available (n = 16); comparator, i.e. not compared with standard argon laser PRP (n = 15); study design, i.e. not randomised controlled trial (n = 12); outcome, i.e. study did not measure relevant outcomes (n =3); patient population, i.e. patients did not have PDR (n = 3), comparisons not pre&#;specified by this review (n = 3). See Characteristics of excluded studies table for the list of exclusions with reasons.

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No study recorded near visual acuity, or patient&#;relevant outcomes such as loss of driving licence or vision&#;related quality of life. No study discussed resource use and costs. Follow&#;up time ranged from one month to two years.

Approximately half of the studies provided some measure of regression or progression of PDR. Visual field loss was only reported in one study and pain during laser treatment was reported in five studies.

All studies except two studies ( Bandello ; Tewari ) measured and reported our primary outcome of loss or gain of at least 15 ETDRS letters (equivalent to 3 ETDRS lines) as measured on a LogMAR chart. If the follow&#;up was not recorded at the one&#; and five&#;year time point we used the final time point provided.

All participants included in the review were treated with an alternative laser PRP strategy compared with standard argon laser PRP (defined as midperipheral scatter, panretinal photocoagulation with 0.1 second pulse duration of moderate laser intensity). We included a variety of alternative laser PRP interventions which included: double&#;frequency Nd:YAG laser (532 nm) ( Bandello )( Brancato ); diode laser (810 nm) ( Bandello ; Han ; Tewari ); longer exposure time of 0.5 second argon laser burn ( Wade ); 'light intensity' lower energy treatment with standard argon laser pulse ( Bandello ); 'mild scatter' argon laser pattern limited to only 400 to 600 laser burns in one sitting ( Pahor ); 'central PRP' which compared a more central (mean number of 437 laser burns placed more posteriorly with sparing of a 2 DD area centred on the fovea and papillomacular bundle) versus a more standard 'peripheral' PRP (mean number of 441 laser burns placed more peripherally, anterior to the equator extending to the ora serrata when possible) treatment in addition to mid&#;peripheral PRP ( Blankenship ); 'central sparing' argon laser PRP distribution which stopped 3 DD from the upper temporal and lower margin of the fovea ( Theodossiadis ); and an 'extended targeted' argon laser PRP to include the entire retina anterior to the equator and any capillary non&#;perfusion areas between the vascular arcades and equator, including 1 DD beyond the ischaemic areas ( Nikkhah ). See more details in the Characteristics of included studies table.

All studies in the review included both male and female adult participants with a clinical diagnosis of type 1 or type 2 diabetes mellitus, between the ages of 18 to 79 years, although age range of participants was not always reported. One or both eyes of each participant were required to have high risk proliferative diabetic retinopathy based on the ETDRS definition, Han being the only study to include only one eye per person. None of the studies that included one or both eyes adjusted the data analysis for within&#;person correlation. There was one within&#;person study ( Tewari ), again with no appropriate, matched, analysis. Across all included studies the baseline mean age ranged from 40 to 58 years, and baseline mean visual acuity ranged from 0.12 to 0.89 LogMAR acuity. The size of studies varied from 20 to 270 eyes.

We included a total of 11 studies in the review, all of which were randomised controlled trials. These studies were conducted in the US (2), Italy (4), South Korea (1), India (1), Iran (1), Slovenia (1), and Greece (1). There was generally poor recording of the sponsorship source, but two studies declared public funding ( Blankenship ; Wade . )

The electronic searches yielded a total of records ( Figure 1 ). The Cochrane Information Specialist scanned the search results, removed duplicates and then removed references which were irrelevant to the scope of the review. We screened the remaining 491 reports and obtained 88 full&#;text reports for further assessment. We included 13 reports of 11 studies (see Characteristics of included studies ), and excluded 69 reports of 52 studies (see Characteristics of excluded studies ). We did not identify any ongoing studies from our searches of the clinical trials registries. We have 6 studies awaiting classification for which we were unable to identify a full text report ( Chaine , Kianersi ; Wroblewski ) or were unable to obtain a translation ( Uehara , Yang ) or for which the full text did not provide enough information to judge inclusion ( Salman ).

We did not have access to trial protocols as the studies were conducted so long ago ( Nikkhah was the only study on a clinical trial registry) so we were unable to judge whether or not selective reporting was likely to be a problem.

In a further two studies, not enough information was given to judge this ( Bandello ; Theodossiadis ).

In Pahor attrition was high (38%) after a follow&#;up of one month after treatment, and it was not reported to which groups the loss to follow&#;up occurred.

In Han the number of participants randomised matched the number of participants analysed but the loss to follow&#;up was not clearly reported. In Han&#;s exclusion criteria there was indication that people with adverse events were excluded after treatment but it was not reported how many people were excluded in this way.

None of the studies masked participants, personnel or outcomes assessors so they were judged at high risk of bias for these domains.

Two studies reported allocation concealment. In Blankenship allocation was done after the participants were recruited. Nikkhah reported that the allocation sequence was kept concealed from the investigators.

Five studies reported an adequate method of random sequence generation: Bandello and Nikkhah used computer&#;generated random numbers; Blankenship , Tewari and Wade flipped a coin. In the remaining studies it was not possible to judge whether random sequence generation had been done properly. Bandello may have used alternate allocation.

Risk of bias summary: review authors' judgements about each risk of bias item for each included study.

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.

Effects of interventions

See: Table 1; Table 2; Table 3; Table 4; Table 5; Table 6; Table 7; Table 8

Summary of findings for the main comparison. Nd:YAG laser compared to argon&#;green laser for proliferative diabetic retinopathy.

Nd:YAG laser compared to argon&#;green laser for proliferative diabetic retinopathy Patient or population: people with proliferative diabetic retinopathy&#; Setting: eye hospital&#; Intervention: Nd:YAG laser&#; Comparison: argon&#;green laser Outcomes Anticipated absolute effects* (95% CI) Relative effect&#; (95% CI) &#; of participants&#; (studies) Certainty of the evidence&#; (GRADE) Comments Risk with argon&#;green laser Risk with Nd:YAG laser BCVA: loss of 15 or more ETDRS letters&#; follow&#;up: 1 year Study population RR 0.80&#; (0.30 to 2.13) 20&#; (1 RCT) &#;&#;&#;&#;&#; VERY LOW 1 2 3   500 per 400 per &#; (150 to ) BCVA: gain of 15 or more ETDRS letters Study population RR 0.33 (0.02 to 7.32) 20&#; (1 RCT) &#;&#;&#;&#;&#; VERY LOW 1 2 3   100 per 33 per &#; (2 to 732) Progression of PDR&#; follow&#;up: 1 year Study population RR 1.00&#; (0.07 to 14.95) 42&#; (1 RCT) &#;&#;&#;&#;&#; VERY LOW 1 2 4   48 per 48 per &#; (3 to 712) Regression of PDR&#; follow&#;up: 1 year Study population RR 1.00&#; (0.87 to 1.14) 42&#; (1 RCT) &#;&#;&#;&#;&#; VERY LOW 1 2 5   952 per 952 per &#; (829 to ) Pain during laser treatment Study population RR 1.00
(0.36 to 2.76) 62
(2 RCTs) &#;&#;&#;&#;&#; VERY LOW 1 6   190 per 190 per &#; (69 to 524) Vision&#;related QoL &#; not reported &#; &#; &#; &#; &#;   Adverse events Vitreous haemorrhage, 13% of argon group, RR 1.22 (0.38 to 3.94); choroidal detachment, 19% of argon group, RR 0.23 (0.04 to 1.27); neurotrophic keratopathy, 10% of argon group, RR 1.29 (0.35 to 4.75). 62 (2 RCT) &#;&#;&#;&#;&#; VERY LOW 1 2 7   *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).&#; &#; CI: Confidence interval; RR: Risk ratio GRADE Working Group grades of evidence&#; High&#;certainty: We are very confident that the true effect lies close to that of the estimate of the effect.&#; Moderate&#;certainty: We are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.&#; Low&#;certainty: Our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect.&#; Very low&#;certainty: We have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect. Open in a new tab

Summary of findings 2. Diode laser compared to argon laser for proliferative diabetic retinopathy.

Diode laser compared to argon laser for proliferative diabetic retinopathy Patient or population: people with proliferative diabetic retinopathy&#; Setting: eye hospital&#; Intervention: diode laser&#; Comparison: argon laser Outcomes Anticipated absolute effects* (95% CI) Relative effect&#; (95% CI) &#; of participants&#; (studies) Certainty of the evidence&#; (GRADE) Comments Risk with argon Risk with Diode BCVA: loss of 15 or more ETDRS letters&#; follow&#;up: 1 year Study population RR 0.95
(0.66 to 1.36) 134&#; (2 RCTs) &#;&#;&#;&#;&#; VERY LOW 1 2 3   345 per 379 per &#; (231 to 628) BCVA: gain of 15 or more ETDRS letters&#; follow&#;up: 1 year Study population RR 0.60
(0.25 to 1.45) 134&#; (2 RCTs) &#;&#;&#;&#;&#; VERY LOW 1 2 3   190 per 119 per &#; (47 to 302) Progression of PDR follow&#;up: 1 year Study population RR 0.90
(0.41 to 2.00) 66 (1 RCT) &#;&#;&#;&#;&#; VERY LOW 1 3 4   286 per 257 per &#; (117 to 571) Regression of PDR&#; follow&#;up: 1 year Study population RR 0.75&#; (0.35 to 1.60) 66&#; (1 RCT) &#;&#;&#;&#;&#; VERY LOW 1 3 4   343 per 257 per &#; (120 to 549) Pain during laser treatment 211 per 688 per
(428 to ) RR 3.07 (2.15 to 4.39) 228 (4 RCTs) &#;&#;&#;&#;&#; MODERATE 1   Vision&#;related QoL &#; not reported &#; &#; &#; &#; &#;   Adverse events Vitreous haemorrhage, 15% of argon group. inconsistent results between two studies, RR 0.50 (0.05, 4.86) and RR 1.82 (0.76, 4.35); choroidal detachment, 8% of argon group RR 4.00 (0.51, 31.13; neurotrophic keratopathy, 0% of argon group, RR 3.00 (0.13, 67.51), maculopathy, 14% of argon group, RR 1.30 (0.54, 3.13), cataract, 16% of argon group, RR 0.52 (0.17, 1.57), pre&#;retinal membrane, 5% of argon group, RR 1.16 (0.24, 5.49). 134 (2 studies) &#;&#;&#;&#;&#; VERY LOW 1 5   *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).&#; &#; CI: Confidence interval; RR: Risk ratio GRADE Working Group grades of evidence&#; High&#;certainty: We are very confident that the true effect lies close to that of the estimate of the effect.&#; Moderate&#;certainty: We are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.&#; Low&#;certainty: Our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect.&#; Very low&#;certainty: We have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect. Open in a new tab

Summary of findings 3. 0.5 compared to 0.1 second exposure for proliferative diabetic retinopathy.

0.5 compared to 0.1 second exposure for proliferative diabetic retinopathy Patient or population: proliferative diabetic retinopathy&#; Setting: eye hospital&#; Intervention: 0.5 second exposure&#; Comparison: 0.1 second exposure Outcomes Anticipated absolute effects* (95% CI) Relative effect&#; (95% CI) &#; of participants&#; (studies) Certainty of the evidence&#; (GRADE) Comments Risk with 0.1 second exposure Risk with 0.5 second exposure BCVA: loss of 15 or more EDTRS letters &#; 1 year Study population RR 0.42
(0.08 to 2.04 44&#; (1 RCT) &#;&#;&#;&#;&#; LOW 1 2   200 per 84 per &#; (16 to 408) BCVA: gain of 15 or more EDTRS letters &#; 1 year Study population RR 2.22
(0.68 to 7.28) 44&#; (1 RCT) &#;&#;&#;&#;&#; LOW 1 2   150 per 333 per &#; (102 to ) Progression of PDR &#; 1 year Study population RR 0.33
(0.02 to 7.14) 16 (1 RCT) &#;&#;&#;&#;&#; VERY LOW 1 3   125 per 41 per &#; (3 to 893) Regression of PDR &#; 1 year Study population RR 1.17&#; (0.92 to 1.48) 32&#; (1 RCT) &#;&#;&#;&#;&#; LOW 1 2   857 per per &#; (789 to ) Pain during laser treatment &#; not reported &#; &#; &#; &#; &#;   Adverse events Pre&#;retinal or vitreous haemorrhage, 30% of 0.1 sec group, (RR 0.56 (0.18 to 1.70)); macular thickening, 2 cases in 0.1 sec group; combined rhegmatous and traction retinal detachment, 1 case in 0.5 sec group. &#; 44 (1 RCTs) &#;&#;&#;&#;&#; VERY LOW 1 3   *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).&#; &#; CI: Confidence interval; RR: Risk ratio GRADE Working Group grades of evidence&#; High&#;certainty: We are very confident that the true effect lies close to that of the estimate of the effect.&#; Moderate&#;certainty: We are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.&#; Low&#;certainty: Our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect.&#; Very low&#;certainty: We have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect. Open in a new tab

Summary of findings 4. Light PRP compared to classic PRP for proliferative diabetic retinopathy.

Light PRP compared to classic PRP for proliferative diabetic retinopathy Patient or population: proliferative diabetic retinopathy&#; Setting: eye hospital&#; Intervention: light PRP&#; Comparison: classic PRP Outcomes Anticipated absolute effects* (95% CI) Relative effect&#; (95% CI) &#; of participants&#; (studies) Certainty of the evidence&#; (GRADE) Comments Risk with classic Risk with Light BCVA: loss of 15 letters or more &#; not reported &#; &#; &#; &#; &#; Mean difference in logMAR acuity at 1 year was &#;0.09, 95% CI &#;0.22 to 0.04; participants = 65; studies = 1. BCVA: gain of 15 letters or more &#; not reported             Progression of DR &#; not reported &#; &#; &#; &#; &#;   Regression of PDR &#; not reported &#; &#; &#; &#; &#;   Pain during laser treatment Study population RR 0.23&#; (0.03 to 1.93) 65&#; (1 RCT) &#;&#;&#;&#;&#; LOW 1 2   129 per 30 per &#; (4 to 249) Adverse events Vitreous haemorrhage, 19% in classic group, RR 0.07 (0.00 to 1.20); choroidal detachment 3 cases in classic group; neurotrophic keratopathy, 2 cases in classic group; clinically significant macular oedema, 23% of classic group, RR 0.13 (0.02 to 1.00). &#; 65 (1 RCTs) &#;&#;&#;&#;&#; VERY LOW 1 3   *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).&#; &#; CI: Confidence interval; RR: Risk ratio GRADE Working Group grades of evidence&#; High&#;certainty: We are very confident that the true effect lies close to that of the estimate of the effect.&#; Moderate&#;certainty: We are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.&#; Low&#;certainty: Our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect.&#; Very low&#;certainty: We have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect. Open in a new tab

Summary of findings 5. Mild scatter PRP compared to full scatter PRP for proliferative diabetic retinopathy.

Mild scatter PRP compared to full scatter PRP for proliferative diabetic retinopathy Patient or population: proliferative diabetic retinopathy&#; Setting: eye hospital&#; Intervention: mild scatter PRP&#; Comparison: full scatter PRP Outcomes Anticipated absolute effects* (95% CI) Relative effect&#; (95% CI) &#; of participants&#; (studies) Certainty of the evidence&#; (GRADE) Comments Risk with Full scatter PRP Risk with Mild scatter PRP BCVA: loss of 15 or more ETDRS letters &#; not reported &#; &#; &#; &#; &#; Mean Snellen decimal acuity was similar in the two groups at 3 months. Mild scatter 0.93 (SD 0.11), full scatter 0.89 (SD 0.19). BCVA: gain of 15 or more ETDRS letters &#; not reported &#; &#; &#; &#; &#;   Progression if PDR &#; not reported &#; &#; &#; &#; &#;   Regression of PDR &#; not reported &#; &#; &#; &#; &#;   Pain during laser treatment &#; not reported &#; &#; &#; &#; &#;   Vision&#;related QoL &#; not reported &#; &#; &#; &#; &#;   Adverse events &#; not reported &#; &#; &#; &#; &#;   *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).&#; &#; CI: Confidence interval; RR: Risk ratio GRADE Working Group grades of evidence&#; High&#;certainty: We are very confident that the true effect lies close to that of the estimate of the effect.&#; Moderate&#;certainty: We are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.&#; Low&#;certainty: Our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect.&#; Very low&#;certainty: We have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect. Open in a new tab

Summary of findings 6. Central PRP compared to peripheral PRP for proliferative diabetic retinopathy.

Central compared to peripheral for proliferative diabetic retinopathy Patient or population: proliferative diabetic retinopathy&#; Setting: eye hospital&#; Intervention: central&#; Comparison: peripheral Outcomes Anticipated absolute effects* (95% CI) Relative effect&#; (95% CI) &#; of participants&#; (studies) Certainty of the evidence&#; (GRADE) Comments Risk with peripheral Risk with Central BCVA: loss of 15 or more ETDRS letters &#; 1 year Study population RR 3.00&#; (0.67 to 13.46) 50&#; (1 RCT) &#;&#;&#;&#;&#; LOW 1 2   80 per 240 per &#; (54 to ) BCVA: gain of 15 or more ETDRS letters &#; 1 year Study population RR 0.25 (0.03 to 2.08) 50&#; (1 RCT) &#;&#;&#;&#;&#; LOW 1 2   160 per 40 per &#; (5 to 333) Progression of DR &#; not reported         &#;   Regression of PDR &#; not reported &#; &#; &#; &#; &#;   Pain during laser treatment &#; not reported &#; &#; &#; &#; &#;   Vision&#;related QoL &#; not reported &#; &#; &#; &#; &#;   Adverse events Vitreous haemorrhage requiring additional PRP, 1 case in each group; macular traction detachment requiring pars plana vitrectomy, 3 cases in central group, 1 case in peripheral group; macular thickening associated with loss of 2 or more lines of visual acuity, 2 cases in each group. &#; 50
(1 RCTs) &#;&#;&#;&#;&#; VERY LOW 1 3   *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).&#; &#; CI: Confidence interval; RR: Risk ratio GRADE Working Group grades of evidence&#; High&#;certainty: We are very confident that the true effect lies close to that of the estimate of the effect.&#; Moderate&#;certainty: We are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.&#; Low&#;certainty: Our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect.&#; Very low&#;certainty: We have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect. Open in a new tab

Summary of findings 7. Centre sparing PRP compared to full scatter PRP for proliferative diabetic retinopathy.

Centre sparing PRP compared to full scatter PRP for proliferative diabetic retinopathy Patient or population: proliferative diabetic retinopathy&#; Setting: eye hospital&#; Intervention: centre sparing PRP&#; Comparison: full scatter PRP Outcomes Anticipated absolute effects* (95% CI) Relative effect&#; (95% CI) &#; of participants&#; (studies) Certainty of the evidence&#; (GRADE) Comments Risk with full scatter PRP Risk with Centre sparing BCVA: loss of 15 or more ETDRS letters&#; follow&#;up: 1 year Study population RR 0.67&#; (0.30 to 1.50) 53&#; (1 RCT) &#;&#;&#;&#;&#; LOW 1 2   385 per 258 per &#; (115 to 577) BCVA: gain of 15 or more ETDRS letters follow&#;up: 1 year &#; not reported &#; &#; &#; &#; &#;   Progression of DR &#; not reported &#; &#; &#; &#; &#;   Regression of PDR&#; follow up: 1 year Study population RR 0.96&#; (0.73 to 1.27) 53&#; (1 RCT) &#;&#;&#;&#;&#; LOW 1 2   808 per 775 per &#; (590 to ) Pain during laser treatment &#; not reported &#; &#; &#; &#; &#;   Vision&#;related QoL &#; not reported &#; &#; &#; &#; &#;   Adverse events &#; not reported &#; &#; &#; &#; &#;   *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).&#; &#; CI: Confidence interval; RR: Risk ratio; OR: Odds ratio; GRADE Working Group grades of evidence&#; High&#;certainty: We are very confident that the true effect lies close to that of the estimate of the effect.&#; Moderate&#;certainty: We are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.&#; Low&#;certainty: Our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect.&#; Very low&#;certainty: We have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect. Open in a new tab

Summary of findings 8. Extended targeted PRP compared to standard PRP.

Extended targeted PRP compared with standard PRP for proliferative diabetic retinopathy Patient or population: people with diabetic retinopathy
Settings: eye hospital
Intervention: extended targeted PRP
Comparison: standard PRP Outcomes Illustrative comparative risks* (95% CI) Relative effect&#; (95% CI) No of Participants&#; (studies) Certainty of the evidence&#; (GRADE) Comments Assumed risk Corresponding risk standard PRP extended targeted PRP BCVA: loss of 15 or more ETDRS letters: follow&#;up 1 year Study population RR 0.94
(0.70 to 1.28) 270 (1 RCT) &#;&#;&#;&#;&#; LOW1 2 Mean difference in BCVA at 1 year was: 0.00 logMAR, (&#;0.05 to 0.05) 393 per 369 per &#; (275 to 503) BCVA: gain of 15 or more ETDRS letters: follow&#;up 1 year, not reported &#; &#; &#; &#; &#; &#; Progression of DR &#; not reported &#; &#; &#; &#; &#; &#; Regression of PDR
follow&#;up 1 year Study population RR 1.11
(0.95 to 1.31) 270
(1 RCT) &#;&#;&#;&#;&#; LOW1 2   644 per 715 per &#; (612 to 844) Pain during laser treatment &#; not reported &#; &#; &#; &#; &#; &#; Vision&#;related QoL &#; not reported &#; &#; &#; &#; &#; &#; Adverse events Quote: "None of the eyes developed tractional retinal detachment during the study. Additionally, no ocular or non&#;ocular AEs related to the study intervention were detected by the investigators or reported by patients" &#;&#;&#;&#;&#; VERY LOW 3   *The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).&#; CI: Confidence interval; RR: Risk Ratio; AE: adverse events GRADE Working Group grades of evidence&#; High&#;certainty: We are very confident that the true effect lies close to that of the estimate of the effect.&#; Moderate&#;certainty: We are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.&#; Low&#;certainty: Our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect.&#; Very low&#;certainty: We have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect. Open in a new tab

'Light laser' intensity PRP versus 'classic' argon (514 nm) laser PRP

One study investigated this comparison (Bandello ). Bandello enrolled 65 eyes (50 people) with high&#;risk PDR (DRS Research Group criteria) and followed up for an average of 22 months. Treatment included 'light intensity' lower energy argon laser PRP treatment to achieve a very light grey biomicroscopic effect on the retina versus 'classic' argon laser PRP to achieve an opaque, dusky, grey&#;white, off&#;white standard burn.

There was no difference in the change in BCVA between the light laser PRP and the classic laser PRP group (MD &#;0.09, 95% CI &#;0.22 to 0.04) (Analysis 4.1).

4.1. Analysis.

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Comparison 4 Light versus classic, Outcome 1 Change in BCVA.

There was low&#;certainty evidence that fewer people had pain during laser treatment in the light laser PRP compared with classic laser PRP group (RR 0.23, 95% CI 0.03 to 1.93) (Analysis 4.2) (Table 4).

4.2. Analysis.

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Comparison 4 Light versus classic, Outcome 2 Pain during laser treatment.

Other relevant outcomes such as BCVA loss or gain of 15 or more letters, NVA, VF loss, vision&#;related QoL measure, details of any resource use and costs and need for further laser PRP treatment after 3 months were not reported.

Adverse event Light
n/N (%) Classic
n/N (%) RR (95% CI) Vitreous haemorrhage 0/34 (0%) 6/31 (19%) 0.07 (0.00 to 1.20) Choroidal detachment 0/34 (0%) 3/31 (10%) 0.13, (0.01 to 2.43) Neurotrophic keratopathy 0/34 (0%) 2/31 (6%) 0.18 (0.01 to 3.67) Clinically significant macular oedema 1/34 (3%) 7/31 ( 23%) 0.13 (0.02 to 1.00) Open in a new tab

We graded the evidence for this comparison as low&#;certainty for the outcomes of 'pain during laser treatment' (Table 4). We downgraded 1 level for high risk of imprecision due to wide confidence intervals, and downgraded 1 level for high risk of performance and detection bias.

'Mild scatter' versus 'full scatter' argon (514 nm) laser PRP

One study investigated this comparison (Pahor ). Pahor enrolled 40 eyes (32 people) with early PDR and followed up for one month. Treatment included 'mild scatter' argon laser PRP with pattern limited to 400 to 600 laser burns (500 μm, 0.1 sec) over one session versus 'full scatter' argon laser PRP with to laser burns (500 μm, 0.1 sec) over two sessions, two weeks apart.

Results are as follows.

• There was no difference in the change in BCVA between the 'full scatter' PRP compared with the 'mild scatter' PRP group (MD 0.04, 95% CI &#;0.06 to 0.14) (Analysis 5.1).

• Very low&#;certainty evidence that people treated with 'full scatter' PRP were more likely to have visual field loss compared with the 'mild scatter' PRP group (MD &#;2.50, 95% CI &#;4.22 to &#;0.78) (Analysis 5.2) (Table 5).

5.1. Analysis.

Comparison 5 Mild scatter PRP vs full scatter PRP, Outcome 1 Change in BCVA.

Change in BCVA Study Mild scatter: mean Snellen decimal acuity (SD) N Full scatter: mean Snellen decimal acuity (SD) N Pahor 0.93 (0.11) 19 0.89 (0.19) 21 Open in a new tabOpen in a new tab

5.2. Analysis.

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Comparison 5 Mild scatter PRP vs full scatter PRP, Outcome 2 Visual field (mean deviation).

Other relevant outcomes such as BCVA loss or gain of 15 or more letters, NVA, progression or regression of DR, pain during laser treatment, vision&#;related QoL measure, details of any resource use and costs and need for further laser PRP treatment after three months were not reported.

The authors made no comment regarding adverse events in this study.

We graded the evidence for this comparison as low&#;certainty for the outcomes of 'Visual field loss at 1&#;year follow&#;up' Table 5. We downgraded 1 level for high risk of imprecision due to small study size and upper confidence interval close to 0 (null effect); and downgraded 1 level for high risk of performance, detection and attrition bias.

'Central' PRP versus 'peripheral' argon (514 nm) laser PRP

One study investigated this comparison (Blankenship ). Blankenship enrolled 50 eyes (40 participants) with high&#;risk PDR (DRS Research Group criteria) and followed up for 6 months. This study compared more central PRP (mean number of 437 laser burns placed more posteriorly with sparing of a 2 DD area centred on the fovea and papillomacular bundle) versus a more standard 'peripheral' PRP (mean number of 441 laser burns placed more peripherally, anterior to the equator extending to the ora serrata when possible) treatment in addition to mid&#;peripheral PRP.

The results were as follows.

• Low&#;certainty evidence that people treated with central PRP were more likely to lose 15 or more letters of BCVA compared with peripheral laser PRP (RR 3.00, 95% CI 0.67 to 13.46) (Analysis 6.1) (Table 6).

• Low&#;certainty evidence that people treated with central PRP were less likely to gain 15 or more letters of BCVA compared with peripheral laser PRP (RR 0.25, 95% CI 0.03 to 2.08) (Analysis 6.2).

• Very low&#;certainty evidence of a similar outcome between people treated with central PRP compared with peripheral laser PRP with regards needing further laser treatment after the initial treatment period (i.e. 3 months) (RR 1.00, 95% CI 0.07 to 15.12) (Analysis 6.3).

6.1. Analysis.

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Comparison 6 Central versus peripheral, Outcome 1 BCVA: loss of 15 or more ETDRS letters.

6.2. Analysis.

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Comparison 6 Central versus peripheral, Outcome 2 BCVA: gain of 15 or more ETDRS letters.

6.3. Analysis.

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Comparison 6 Central versus peripheral, Outcome 3 Needing further laser treatment after initial treatment period i.e. after 3 months..

Other relevant outcomes such as NVA, progression or regression of DR, VF loss, pain during laser treatment, vision&#;related QoL measure, details of any resource use and costs and need for further laser PRP treatment after three months were not reported.

Adverse event Central
n/N (%) Peripheral
n/N (%) RR (95% CI) Vitreous haemorrhage (requiring additional PRP) 1/25 (4%) 1/25 (4%) RR 1.00 (0.07 to 15.12) Macular traction detachment (requiring pars plana vitrectomy) 3/25 (12%) 1/25 (4%) RR 3.00 (0.33 to 26.92) Macular thickening (associated with loss of 2 or more lines of visual acuity) 2/25 (8%) 2/25 (8%) RR 1.00 (0.15 to 6.55) Open in a new tab

We graded the evidence for this comparison as low&#;certainty for the outcomes of 'BCVA loss of 15 or more ETDRS letters at 1 year' (Table 6). We downgraded 1 level for high risk of imprecision due to wide confidence interval; and downgraded 1 level for high risk of performance and detection bias.

'Centre sparing' versus 'full scatter' argon (514 nm) laser PRP

One study investigated this comparison (Theodossiadis ). Theodossiadis enrolled 53 eyes (42 participants) with high&#;risk PDR (DRS Research Group criteria) and followed up for 6 months. This study used argon laser PRP burns ( to burns of 200 μm to 500 μm diameter). In the centre sparing group, laser PRP covered the entire retinal periphery and midperiphery beginning 1 disc diameter from the pars plana, but the posterior pole was spared 2 disc diameter areas centred on the fovea and including the papillomacular bundle. In the full scatter group, laser PRP involved the periphery and midperiphery but stopped 1 disc diameter short of the nasal margins of the optic disc and 3 disc diameter away from the upper, lower and temporal margins of the fovea.

The results were as follows.

• Low&#;certainty evidence that people treated with centre sparing PRP were less likely to lose 15 or more ETDRS letters of BCVA compared with full scatter laser PRP (RR 0.67, 95% CI 0.30 to 1.50) (Analysis 7.1; Table 7).

• Low&#;certainty evidence that people treated with centre sparing PRP had similar regression of PDR compared with full scatter laser PRP (RR 0.96, 95% CI 0.73 to 1.27) (Analysis 7.2).

7.1. Analysis.

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Comparison 7 Centre sparing versus full scatter PRP, Outcome 1 BCVA: loss of 15 or more ETDRS letters.

7.2. Analysis.

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Comparison 7 Centre sparing versus full scatter PRP, Outcome 2 Regression of PDR.

This study concluded "no statistically significant difference regarding regression of neovascularisation and visual acuity" between the two groups. "There was a difference in retinal sensitivity in favour of group B at 15 and 30 degrees of visual field found" (Theodossiadis ).

Other relevant outcomes such as BCVA gain of 15 or more letters, NVA, regression of DR, vision&#;related QoL measure, details of any resource use and costs and need for further laser PRP treatment after three months were not reported.

The authors made no comment regarding adverse events in this study.

We graded the evidence for this comparison as low&#;certainty for the outcomes of 'BCVA loss of 15 or more ETDRS letters at 1 year' and 'Regression of PDR at 1&#;year follow&#;up' (Table 6). We downgraded 1 level for high risk of imprecision due to wide confidence interval, and downgraded 1 level for high risk of performance and detection bias.

'Extended targeted' PRP versus 'standard' argon (514 nm) laser PRP

One study investigated this comparison (Nikkhah ). Nikkhah enrolled 270 eyes (234 participants) with early or high&#;risk PDR (DRS Research Group criteria) and followed up for three months. Treatment in both arms applied to argon laser burns with spot size of 200 μm, duration 200 ms and spacing of 0.5 burn width. In the extended targeted PRP (ETRP) group the laser was applied to the entire retina anterior to the equator as well as the capillary non&#;perfusion areas between the vascular arcade and the equator. Conventional PRP (CPRP) laser was applied from the vascular arcade toward the midperiphery.

The results were as follows.

• Low&#;certainty evidence that people in the extended targeted PRP had similar or slightly reduced chance of loss of 15 or more letters of BCVA compared with the standard PRP group (RR 0.94, 95% CI 0.70 to 1.28) (Analysis 8.1) (Table 8).

• Low&#;certainty evidence that people in the extended targeted PRP had similar or slightly increased chance of regression of PDR compared with the standard PRP group (RR 1.11, 95% CI 0.95 to 1.31) (Analysis 8.3).

8.1. Analysis.

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Comparison 8 Extended targeted PRP versus standard PRP, Outcome 1 BCVA: loss of 15 or more letters.

8.3. Analysis.

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Comparison 8 Extended targeted PRP versus standard PRP, Outcome 3 Regression of PDR.

Other relevant outcomes such as BCVA gain of 15 or more letters, NVA, progression of DR, VF loss, pain during laser treatment, vision&#;related QoL measure, details of any resource use and costs and need for further laser PRP treatment after three months were not reported.

No adverse events were observed. "None of the eyes developed tractional retinal detachment during the study. Additionally, no ocular or non&#;ocular AEs related to the study intervention were detected by the investigators or reported by patients" (Nikkhah ).

We graded the evidence for this comparison as low&#;certainty for the outcomes of 'BCVA loss of 15 or more ETDRS letters at 1 year' and 'Regression of PDR at 1&#;year follow&#;up' (Table 8). We downgraded 1 level for high risk of imprecision due to wide confidence interval; and downgraded 1 level for high risk of performance and detection bias.

Laser is an abbreviation for (Light Amplification by Stimulated Emission of Radiation). The concept of ocular therapy using light was published first by Meyer-Schwickerath, who used the sunlight to treat patients with ocular melanoma in . On the other hand, many experiments on retinal damage from sunlight were performed in the late 's, but they are not published.

Laser Properties

Monochromatic, Coherent, & Collimated

Lasers have properties to produce highly monochromatic coherent beam that is collimated and has limited divergence. Monochromatic electromagnetic wave means that it has single wavelength eliminating chromatic aberration. Coherence of lasers is classified as either spatial or temporal. Spatial coherence allows precise focusing of the laser beam to widths as small as a few microns, while temporal coherence allows selection of specific monochromatic wavelengths within a single laser or a group of lasers. Practically, spatial coherence, allow extremely small burns to pathologic tissue, with minimal disturbance to surrounding normal tissue; on the other hand, temporal coherence allows treatment of specific tissue sites by selecting laser wavelengths that are preferentially absorbed by these tissue sites.

Principles of Laser Emission

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Atoms are composed of a positively charged nucleus and negatively charged electrons at various energy levels. Light is composed of individual packets of energy, called photons. Electrons can jump from one orbit to another by either absorbing energy and moving to a higher level (excited state), or emitting energy and transitioning to a lower level. Such transitions can be accompanied by absorption or spontaneous emission of a photon.

&#;Stimulated Emission&#; is the interaction of an atom in the excited state with a passing photon leading to photon emission. The emitted photon by the atom in this process will have the same phase, direction of propagation, and wavelength as the &#;stimulating photon&#;. The &#;stimulating photon&#; does not lose energy during this interaction it simply causes the emission and continues on. For this stimulated emission to occur more frequently, the optical material should have more atoms in an excited state than in a lower state.

Laser System and Media

The lasering medium is contained in an optical cavity (resonator) with mirrors at both ends, which reflect the light into the cavity and thereby circulate the photons through the lasing material multiple times to efficiently stimulate emission of radiation from excited atoms. One of the mirrors is partially transmitting, thereby allowing a fraction of the laser beam to emerge. The lasing medium can be Solid (e.g, Ruby laser, neodymium-doped yttrium aluminum-garnet (Nd:YAG) ), Liquid : (e.g Fluorescent dye ) or Gas (e.g, Argon , Krypton ). Lasers can be pumped by continuous discharge lamps and by pulsed flash lamps. Laser pulse durations can vary from femtoseconds to infinity.

Laser- Tissue Interaction

Laser-tissue interactions can occur in several ways:

Photothermal (photocoagulation and photovaporization)

Photothermal effects include photocoagulation and photovaporization. In photocoagulation, absorption of light by the target tissue results in a temperature rise, which causes denaturization of proteins. Typically, argon, krypton, diode (810nm) and Frequency doubled ND:YAG lasers cause this type of effect. Photovaporization occurs when higher energy laser light is absorbed by the target tissue, resulting in vaporization of both intracellular and extracellular water. The advantage of this type of tissue response is that adjacent blood vessels are also treated, resulting in a bloodless surgical field. The carbon dioxide laser, with its wavelength in the far infrared (10,600 nm), uses this method of action.

Photochemical (photoablation and photoradiation)

Photochemical effects include photoradiation and photoablation. In photoradiation, intravenous administration of photosensitizing agent, which is taken up by the target tissue, causes sensitization of the target tissue. Exposure of this sensitized tissue to red laser light (690 nm) induces the formation of cytotoxic free radicals. Photoablation occurs when high-energy laser wavelengths in the far ultraviolet (< 350 nm) region of the spectrum and are used to break long-chain tissue polymers into smaller volatile fragments. The exposure times in the photoablation process is usually much shorter (nanoseconds) compared to photoradiation. Photodynamic therapy (PDT) is an example of photoradiation therapy while Excimer laser is a photoablative process.

Photoionizing (photodisruption)

In Photoionization high-energy light ( nm) is deposited over a short interval to target tissue, stripping electrons from the molecules of that tissue which then rapidly expands, causing an acoustic shock wave that disrupts the treated tissue. The ND:YAG laser works via a photodisruptive mechanism.

Laser Types in Retina

Argon blue-green laser (70% blue (488 nm) and 30% green(514nm))

Absorbed selectively at retinal pigment epithelial layer (RPE), hemoglobin pigments, choriocapillaries, inner and outer nuclear layer of the retina. It coagulates tissues between the choriocapillaris and inner nuclear layer. The main adverse effects of these lasers are high intraocular scattering, macular damage in photocoagulation near the fovea, and choroidal neovascularization (if Bruch's membrane is ruptured).

Frequency-doubled Nd-YAG Laser (532 nm)

Highly absorbed by hemoglobin, melanin in retinal pigment epithelium and trabecular meshwork. It can be used either continuously or in pulsed mode.

PASCAL (Pattern Scan Laser) is one such type of laser that incorporates semi-Automated multiple pattern, short pulse, multiple shots with precise burn in very short duration using frequency-doubled Nd-YAG Laser (532 nm). It is commonly used nowadays in treatment of many retinal conditions (proliferative diabetic retinopathy, diabetic macular edema, vein occlusions etc.). It has many advantages when compared with conventional single spot laser, as it is produced at a very short duration (10-20 msec) compared to (100-200 msec) of conventional single spot one which leads to less collateral retinal damage. Other advantages include relatively stable scar size, less destructive same efficiency. It also permits the application of different patterns that gives more regular spots on retina with less duration.

Krypton red (647 nm)

Well absorbed by melanin and can pass through hemoglobin which makes it suitable for treatment of subretinal neovascular membrane. It also has low intraocular scattering with good penetration through media opacity or edematous retina and has ability to coagulate the choriocapillaries and the choroid.

Diode laser (805-810 nm)

It is well absorbed by melanin. The near to infrared spectrum (near invisible) makes it more comfortable to use due to absence of flashes of light. It has very deep penetration through the retina and choroid making it the laser of choice in treatment of Retinopathy of Prematurity (ROP) and some types of retina lesions. It is also used via trans-scleral route to treat the ciliary body in some cases of refractory glaucoma.

Laser-Tissue Absorption in the Retina

Melanin

Found mainly in the RPE (Retinal pigment epithelium) and choroid, and absorbs mainly wavelength between 400-700 nm. The longer the wavelength of light, the more the melanin is penetrated. For example, Diode laser with wavelength of 810 nm can penetrate deeply into the choroid.

Macular xanthophyll

Located in the inner and outer plexiform retinal layers. It protects the photoreceptors from short-wavelength light damage, but can be damaged by blue light which is why Argon green is preferred in macular photocoagulation over Argon blue.

Hemoglobin

Absorption varies according to oxygen saturation. It absorbs yellow, green, and blue wavelengths, but red light is absorbed poorly. Thus, macular lasers may, uncommonly, damage retinal vessels.

Laser delivery systems

Slit lamp

It is the most popular and common delivery system. Laser settings such as power, spot size and exposure time can be changed easily.

Indirect ophthalmoscope

Commonly used via a fiberoptic cable to deliver diode or argon lasers. It is ideal in the treatment of peripheral retina e.g. peripheral breaks and cases of retinopathy of prematurity. The spot size is altered by the dioptric effect of the condensing lens used. It may even vary depending on the refractive status of the eye (i.e. in hyperopic eyes the spot size will be smaller, and in myopic eyes it will be larger).

Endophotocoagulation

It delivered mainly argon green and diode lasers. Often used during retinal detachment repair following pars plana vitrectomy and extrusion of the subretinal fluid or in the surgical treatment of proliferative diabetic retinopathy.

Micropulse laser therapy

Micropulse laser describes a method of retinal laser delivery and can be applied with lasers of different wavelengths, such as 532 nm, 577 nm, or 810 nm. This type of delivery essentially divides the treatment into repeated microsecond impulses with intervals separating these where the retinal tissue is allowed to cool down. The laser power is set to a low level, and in general, the spots are not visible on the retina; the intention is to treat the retina on a subclinical basis while avoiding thermal damage to the underlying retina that can occur with conventional photocoagulation. While this type of laser therapy appears to be safe, its efficacy continues to be debated.[1]

Lenses Used for Laser Delivery

Selection of lens depend on many factors include, desired field of view, amount of magnification, area to be treated, and ophthalmologist preference. The commonly used contact lenses for panretinal and focal/grid retinal photocoagulation are listed in table 1 and 2. It is important to remember that most of the commonly used lenses magnify the image size; thus, the laser spot size on the machine must be set accordingly.

Table 1. Contact Lenses used for PRP Lens Image Magnification Laser Spot Magnification Field of View Goldmann 3-mirror 0.93x 1.08x 140­­&#; Mainster Widefield 0.68x 1.5x 118-127&#; Mainster PRP 165 0.51x 1.96x 165-180&#; Volk Quadraspheric 0.51x 1.97x 120-144&#; Volk Super Quad 160 0.50x 2.00x 160-165&#; Table 2. Contact Lenses used for Focal/Grid Lasers Lens Image Magnification Laser Spot Magnification Field of View Goldmann 3-mirror 0.93x 1.08x 140­­&#; Mainster standard 0.96x 1.05x 90-121&#; Mainster high magnification 1.25x 0.8x 75-88&#; Ocular PDT 1.6X 0.63x 1.6x 120-133&#; Volk area centralis 1.06x 0.94x 70-84&#;

Panretinal Photocoagulation for Treatment of Proliferative Diabetic Retinopathy

The Diabetic Retinopathy Study (DRS) established panretinal photocoagulation (PRP) as an effective treatment for high risk PDR which includes eyes with one of the three of the following risk factors: NVD greater than 1/3 disc area, any NVD with vitreous hemorrhage or NVE greater than half a disc area with preretinal or vitreous hemorrhage. The Early Treatment Diabetic Retinopathy Study (ETDRS) recommended careful follow-up without PRP for mild or moderate nonproliferative diabetic retinopathy. Laser settings for conventional retinal laser photocoagulation for diabetic retinopathy is typically performed with a continuous wave (cw) laser at 514 or 532 nm with exposure durations from 100 to 200 ms, spot sizes from 100 to 500 µm, and powers from 250 to 750 mW. If Patterned scanning laser is used, it typically utilizes settings of 532 nm wavelength, 200 µm spot size, 20 ms duration, and powers from 300 to 750 mW. Area of treatment reaches approximately &#; 500 micron-sized burns spaced between one half and 1 burn width apart, beginning temporally just outside the vascular arcades and 3-disc diameters temporal to the macula, and extending to or just beyond the equator. Some providers prefer to divide treatment into two or more sessions while others elect to perform treatment in a single session. On the nasal side of the fundus, burns begin about 1-disc diameter nasal to the optic disc and also extend to or just beyond the equator. However, specific regimens vary by practitioner.

Treatment of Diabetic Macular Edema with Laser Photocoagulation

The ETDRS recommended macular laser for Clinically significant macular edema (CSME) which was defined as any of the following based on stereoscopic fundus examination:

1. Retinal thickening within 500 µm of the foveal center;
2. Hard exudates within 500 µm of the foveal center associated with adjacent retinal thickening; or
3. Retinal thickening more than 1 disc area in size within 1 disc diameter from the foveal center

Focal photocoagulation is directed to microaneurysms more than 500 µm away from the foveal center. Treatment up to 300 µm from the foveal center is allowed if vision is 20/40 or worse. Grid photocoagulation is applied to areas of diffuse leakage and capillary non-perfusion on fluorescein angiography. Focal laser setting is a 50 to 100 µm spot size, 50 to 100 ms pulse duration, and power titrated to barely whiten the microaneurysm. Grid laser setting is a 50 to 200 µm spot size, 50 to 100 ms pulse duration, and power titrated to achieve mild burn intensities.

Transpupillary Thermotherapy (TTT)

A more intense, destructive modality, this is occasionally used for the treatment of choroidal melanomas, retinoblastoma, subfoveal choroidal neovascular membranes (CNVM) and other ocular tumors. TTT involves long exposures (~60 s) of a large spot (1.2&#;3 mm) at low irradiance (~10 W/cm2), using a near-infrared Diode (810 nm) laser that is thought to induce intralesional hyperthermia and subsequent vascular occlusion and lesion shrinkage.

Laser Photocoagulation in Branch and Central Retinal Vein Occlusions

In branch or central vein occlusions, retinal hypoxia occurs in the distribution of the occluded veins and may elicit a neovascular response in the affected area. Sector or panretinal photocoagulation is then the treatment of choice. It has been shown that macular grid laser photocoagulation can be used to treat persistent macular edema (> 3 months, vision worse than 20/40) resulting from branch vein occlusion with improvement of vision in some cases, although anti-vascular endothelial growth factor (anti-VEGF) intravitreal injections have become the standard of care.

Laser Photocoagulation in Age-Related Macular Degeneration and Related Diseases

Thermal Laser Photocoagulation

Before the era of intravitreal injections, thermal photocoagulation with the argon blue-green laser or krypton red was the first-line of treatment for exudative age-related macular degeneration (AMD) in cases of extrafoveal CNVM. However, treatment of subfoveal and juxtafoveal lesions usually yielded a dense scotoma with a high recurrence rates for the CNVM.

Photodynamic Therapy (PDT)

PDT is a form of selective laser therapy, leading to closure of the choroidal neovascular process and other active proliferating vessels, while leaving normal retinal tissue unharmed. It was first described to treat exudative AMD and studied in the VIP/TAP clinical trials, although the gold standard in treating exudative AMD has since become anti-VEGF therapy. [2]. It works by photoradiation mechanism in which previously hematoporphyrin derivative and currently verteporfin (Visudyne) is used as a photosensitizing agent followed by local application of light in the absorption spectrum of that agent (i.e. 689 nm). This will release free radicals that destroy endothelial cells causing closure of hyperproliferative vessels, as in an actively growing tumor, or in an area of active choroidal neovascularization. It remains a useful adjuvant therapy for other intraocular vascular disorders, as well as posterior segment neoplasms. PDT is now frequently used for cutaneous and subcutaneous tumors. Treatment with PDT should be guided by a recent fluorescein angiography or indocyanine green study. A light dose of 50 J/cm2 (full-fluence PDT), or 25 J/cm2 (half-fluence PDT) has been described for the treatment of choroidal neovascularization of various conditions, in addition to other choroidal vascular pathologies, including chronic central serous choroidopathy, polypoidal choroidal vasculopathy, as well as choroidal neoplasms, such as circumscribed choroidal hemangiomas.

Additional Resources

References

1. &#;

   Gawecki M. Micropulse Laser Treatment of Retinal Diseases. J Clin Med. Feb; 8(2): 242.

2. &#;

   Photodynamic therapy of subfoveal choroidal neovascularization in age-related macular degeneration with verteporfin. Two year results of 2 randomised clinical trials&#;TAP report 2. Arch Ophthalmol ;119:198&#;207.

   If you are looking for more details, kindly visit Indocyanine Green Angiography.

3. Palanker DV, Blumenkranz MS, Marmor MF, Fifty years of ophthalmic laser therapy, Arch Ophthalmol.  Dec;129(12):-9. doi: 10./archophthalmol..293.
4. Retina and Vitreous, section 7. Basic and Clinical Science Course, AAO, -.
5. Lasers in Ophthalmology, Basic, Diagnostic, and Surgical Aspects : a Review, by Franz Fankhauser and Sylwia&#; Kwasniewska, .
6. Step by steps, laser in Ophthalmology,by Bikas Bahattacharyya, .
7. Daniel Palanker, PhD, www.AAO.org, comprehensive ophthalmology Lasers Basic properties , .
8. The Diabetic Retinopathy Study Research Group. Photocoagulation treatment of proliferative diabetic retinopathy. Clinical application of Diabetic Retinopathy Study (DRS) findings, DRS Report Number 8. Ophthalmology. ;88:583&#;600.
9. Early Treatment Diabetic Retinopathy Study Research Group. Early photocoagulation for diabetic retinopathy. ETDRS report number 9. Ophthalmology. ;98 (5 Suppl):766-785.
10. Muqit MM, Marcellino GR, Henson DB, Young LB, Turner GS, Stanga PE. Pascal panretinal laser ablation and regression analysis in proliferative diabetic retinopathy: Manchester Pascal Study Report 4. Eye. ;25(11):-.
11. Early Treatment Diabetic Retinopathy Study Research Group. Photocoagulation for diabetic macular edema. Early Treatment Diabetic Retinopathy Study report number 1. Arch Ophthalmol.;103(12):-.
12. Early Treatment Diabetic Retinopathy Study Research Group. Treatment techniques and clinical guidelines for photocoagulation of diabetic macular edema. Early Treatment Diabetic Retinopathy Study Report Number 2. Ophthalmology. ;94(7):761-774.
13. T, Maurage CA, Mordon S. Transpupillary thermotherapy (TTT) with short duration laser exposures induce heat shock protein (HSP) hyperexpression on choroidoretinal layers. Lasers Surg Med. ;33(2):102-107.
14. Complications of Age-related Macular Degeneration Prevention Trial (CAPT) Research Group. Risk factors for choroidal neovascularization and geographic atrophy in the complications of age-related macular degeneration prevention trial. Ophthalmology. ;115(9):-.
15. Moo-Young GA: Lasers in opthalmology, In High-tech medicine. West J Med Dec; 143:745-750.
16. Verteporfin in Phododynamic Therapy Study Group. Verteporfin Therapy of subfoveal choroidal neovascularisation in age-related macular degeneration: Two-year results of a randomised clinical trial including lesions with occult with no classic choroidal neovascularisation&#;Verteporfin in photodynamic therapy report 2. Am J Ophthalmol ;131:541&#;60.
17. TAP study group. Photodynamic therapy of subfoveal choroidal neovascularisation in age-related macular degeneration with verteporfin. Two year results of 2 randomised clinical trials&#;TAP report 2. Arch Ophthalmol ;119:198&#;207.