Dr.SUMAN LATA,
Dr.SHREYAS TEMKAR,Dr.Ramanjit Sihota
Purpose- Comparative evaluation of ASOCT, IOP & UBM changes after PRP by PASCAL and
conventional laser
Methods- This was a prospective, randomized, interventional clinical trial.Consecutive 35patients with PDR requiring PRP. The participants were divided into two groups by including 35 eyes in each group, PASCAL and conventional laser. ASOCT, UBM and OCT were performed to analyze anterior chamber angle,ciliary body thickness, RNFL thickness and GCC thickness. All parameters were measured at baseline and at 1hour,6hours,1day,1week,4weeks,8weeks,12 weeks following PRP. The primary outcome measure were change in IOP,anterior chamber angle,ciliary body thickness,RNFL thickness and GCC thickness before and after PRP.
Results-There was a significant rise in IOP noted at 1hour and 6 hours post PRP in both groups,with >5mmHg rise in 23 out of 35 eyes (71.4%) in PASCAL group and 5 out of 35 eyes (14.2%) in conventional laser group. On day1, a narrowing of the angle was noted, a decrease of more than 5 degrees of iridocorneal angle was noted in 12 out of 35 eyes (34.2%) in PASCAL and 15 out of 35 eyes(42.8%) in the conventional group, 27 out of 70 eyes (38.5%) overall percentage change. An increase in ciliary body thickness was noted at day1 following PRP,more in conventional group and was significant at day 1 post PRP. A nonsignificant change of retinal nerve fiber layer thickness and ganglion cell layer complex thickness was noted at all follow ups at 1hour,6 hours,1 day,1week,4weeks,8weeks and 12 weeks. All angle changes came back to normal at 1 week follow up and continued to be same at 3 month follow up.
Conclusion-PASCAL laser caused a significant IOP spike post PRPand angle narrowing which warrants close follow up in patients of DR with compromised optic nerve function or a preexisting narrow angle.
Panretinal photocoagulation is standard treatment to control proliferative diseaseand decreases the risk of severe vision loss1,in Diabetic Retinopathy Study. Early Treatment Diabetic Retinopathy Study 2 has provided indications, and guidelines forphotocoagulation in PDR.The PASCAL, Pattern scan laser, a 532-nm doublefrequency Neodymium yttrium aluminium garnet (ND-YAG) laser has been shown to be less destructive with fewer retinal complications3,4,5,6,7,8,9.
A high prevalence of POAG in patients with diabetes and vice versa has been shown by many studies, Blue Mountain Eye Study10,Rotterdam Studyand the Beaver Dam Study11 in Wisconsin.(Mitchell P et al and Quigley HA et al.) PACG has also been seen frequently in diabetics.
The effects of PRP and subsequent changes as in IOP, anterior chamber angle narrowing and ciliary body may adversely effect patients with a preexisting compromised optic nerve function and preexisting narrow anterior chamber angle.
Thus our study aimed to record and compare changes in IOP, anterior chamber angle,ciliary body upto 3 months following panretinal photocoagulation using PASCAL or conventional laser.
METHODOLOGY
The study was designed as a prospective,interventional,randomized clinical trial, with clearance obtained from our institutional ethics committee.
Consecutive patients over 18 years of age, with diabetes mellitus type I or type II who met the ETDRS criteria for severe NPDR and PDR without high risk characteristicsreferred to the Retina service for a PRP were evaluated. A detailed history and comprehensive ophthalmic examination was performed for all patients, including slit lamp biomicroscopy and fundus evaluation, to identify patients who met the criteria below.
Inclusion criteria-Treatment naive patients with ETDRS visual acuity between 1 and 0 log units (Snellen equivalent of 6 ⁄ 60 or better) with Mean CRT of less than 300 microns as measured by OCT scans with absence of central intra- and ⁄ or subretinal fluid with Adequate pupil dilatation and clear media to perform laser photocoagulation, digital photography and OCT scans.
Exclusion Criteria– DiabeticPatients with Poor glycemic control with HbA1C greater than 8.0 mg⁄ dlwith proliferative diabetic retinopathy without high risk characteristics
and uncontrolled hypertension, Blood pressure >140⁄ 90 mmHgwith previous laserand Anti VEGF treatment with anyLens opacities or cataract that could influence vision and results and hamper in treatment. Patients with any other ocular pathologies and previously vitrectomised eyes and if any allergy to brimonidine.
The sample size was calculated to be 60, 30 in each group. 70 consecutive patients were enrolled to allow for any dropouts,and a randomization sequence was generated using randomly permuted blocks and a randomization table, with 1:1 allocation to the PASCAL or conventional laser group. Therefore 35 patients with severe NPDR or non high risk PDR were in each group. Our study adhered to the tenets of the Helsinki Declaration.
All patients had an applanation tonometry and pachymetry, at least 3 readings at baseline along with diurnal phasing at baseline,and at 1 and 6hours,1 day,1 week, 4weeks,8 weeks and 3months post panretinal photocoagulation. Pachymetry was done on NIDEK TONOREF-2, Japan. Ultrasound biomicroscopy using (Vumax, Sonomedescalon) and anterior segment optical coherence tomography using (Visante OCT, Carl Zeiss Meditec, inc.Dublin ,CA,USA) were done at baseline and on each follow up visit. Spectral domain optical coherence tomography (SD-OCT) (Cirrus HD-OCT Model 5000, Carl Zeiss Meditec Inc., Dublin,CA,USA) was performed by a single, certified optometrist before and at day1,1 week,4 weeks and 3months following panretinal photocoagulation. Both a macularcube(512*128) and optic disc cube (200*200)scan was done. The treating ophthalmologist reviewed the OCT scans prior to inclusion in the study and on subsequent examinations.
Laser Treatment
Patients underwent panretinalphotocoagulation,either single session of Pattern Scan Laser (PASCAL, Topcon, Santa Clara, CA, USA) or two sessions of conventional laser (Visulas 532 s, Carl Zeiss Meditec ,Dublin,CA,USA)divided over 2 weeks. Laseredareas included retina outside the vascular arcades superiorly and inferiorly, 500 micron nasal to the disc and 3000 micron temporal to fovea, extending as anterior as possible. Pascal 5*5 array with 20 ms pulse duration using QuadrAspheric lens (Volk Optical Inc., OH, USA) with a magnification factor of 0.5 and retinal spot size of 200micron, PRP was performed in a single sitting, whereas in conventional group a retinal spot size of 200-300 micron was placed with 100-200ms pulse duration, and completed in 2 sittings, inferior retinafirst followed by superior retina. The laser spots were placed 1 burn width apart and end point of laser was taken to be moderate grey burns. The total number of laser spots applied differed in both groups, the PASCAL group received2400-2600, versus conventional laser 1600-1800. All patients were prescribed brimonidine at the end of procedure, to be instilled after 6 hours post photocoagulation IOP recording.
Statistical analysis was performed using SPSS (Version 22.0). For pre and post laser analysis, paired t- test was used to evaluate changes in IOP, CCT, AOD 500, TISA 500, TISA 750.ICA, CBT, IRT, RNFL and GCC. For nonparametric data Wilcoxon rank-sum test was used. For intergroup analysis between PASCAL and conventional laser groups, two-sample t test was used for parametric data and Mann Whitney test was used for non-parametric data. A p value of less than 0.05 was taken as significant.
RESULTS-
92 patients were screened, and 70 consecutive patients who met our inclusion and exclusion criteria,were randomized to a PRP using PASCAL or conventional laser. The average age of patients in PASCAL and conventional laser group was 52.94+/-10.21 years and 54.8+/-9.74 years respectively, p-0.43. The female:male distribution was 16 : 19 in the PASCAL group and 17 : 18 in conventional group, p-0.29. The known duration of diabetes among patients in PASCAL and conventional group was 15.74+/-7.42years and 13.31+/-4.6 years, p =0.32.
The baseline clinical, ASOCT and UBM parameters in both groups were comparable, Table 1.
The total number of laser applications used differed between two groups with the mean number of spots used during PASCAL being 2100+/-300and that using conventional laser was1400+/-200spots,divided in 2 sittings.
A rise in IOP was noted at 1 hour and 6 hours in both groups, PASCALrange 14 to 26 mmHg, and conventional laser range 10 to 22mmHg after PRP. A rise in IOP of>6 mmHg was seen in 23 /35 eyes, 71.4%, in PASCAL group and 5/35 eyes, 14.2%, in conventional laser group, and rise of >8mmHg in 8/35 eyes, 22.8%, in the PASCAL group and none of the eyes in conventional laser group.The IOP returned to baseline by day 1 and continuedat the same level till 3 months post laser.The percentage change in IOP in both groups postlaser was significantly greater in PASCAL group as compared to conventional group at 1 hour and 6hours, p<0.001, Figure 1
On ASOCT, AOD 500, AOD 750, TISA 500, TISA 750, all showed a significant decrease at day 1 as compared to baseline. The difference was statistically significant between the groups for AOD750 and TISA500,p=0.03,0.04 respectively and nonsignificant for AOD500 and TISA 750,p=0.42,0.55 respectivelyFig 2 ,3,4,5 shows percentage change in AOD500, AOD 750, TISA 500,TISA 750 in both groups. The angle changes came back to baseline by 1 week and continued to be the same at 3 months. Table 3
On UBM, both groups showed a significant decrease in iridocorneal angle at day 1, which was statistically similarbetween the groups. Baseline iridocorneal angle in the PASCAL group was 32.98+/-4.460 and conventional 33.24+/-4.270. A decrease of more than 5 degrees was noted in 12/35 eyes, 34.2%, in PASCAL treated eyes and 15/35 eyes, 42.8%, in the conventional laser group.The iridocorneal angle came back to baseline at 1 week of follow up and continued to be same up to 3 months.Figure 6 shows percentage decrease in ICA in both groups both pre and post PRP.
The ciliary body thickness on UBM showeda statistically significant increase in both groups at day 1 and thereafter up to 3 months, significantly more in the conventional laser group.No significant change in IRT and RNFL thickness was noted in either group at all follow ups.
DISCUSSION
Panretinal photocoagulation is one of most effective treatment modality used today for treatment of diabetic retinopathy12,with relatively few complications, even thoughnewer agents, like intravitreal steroids and vascular endothelial growth factor inhibitors,are in treand as well. The Diabetic Retinopathy Study and Early Treatment Diabetic Retinopathy Study13,14 had recommended that no more than 900 spots should be given per session, because of possible complications, even though some studies have shown that a single session has no long-termdetrimental effect15. Conventional 532 nm laser places a single spot at a time16, whereas the pattern scan laser,PASCAL,a 532-nm doublefrequency Neodymium yttrium aluminium garnet (ND-YAG) is a multispot laser with multiple patterns17,and has been shown to be safe and well tolerated and allows for precise,uniform pattern laser burns. PRP associated intraocular pressure changes and anterior chamber angle changes have been studied largely after Argon laser PRP.
Our study comprised of 70 eyes with PDR and severe NPDR requiringPRP. All eyes underwent PRP, in single sitting using PASCAL and two sittings using a conventional laser.PASCAL laser system required a greater power than conventional laser (450 mWvs 250 m W) to achieve grade 3 burns as previously reported18.The laser fluence, (power ´ time/area) was significantly less with PASCAL laser as compared with conventional laser for the same burn intensity and spot size.
IOP rise after PRP can result from open or closed angle mechanisms. open angle mechanism includes, aqueous outflow blockadge due to compression of episcleral veins by flanges of fundus contact lens used during PRP delivery, movement of fluid from choroid into vitreous cavity secondary to breakdown of blood retinal barrier, decreased uveoscleral outflow from congestion of ciliary body. Pathogenesis of closed angle mechanism is thought to be swelling of ciliary body or movement of fluid from choroid into the vitreous secondary to damage to blood retinal barrier, both of these can lead to anterior displacement of lens iris diaphragm and hence a rise in IOPAmerican acad.
| vaiables | Blondeau et al19(1981) | Schiodte et al20(1982) | Kaufman et al21(1987) | Mensher et al22(1977) | Agarwal et al23(2017) | Present study |
| Before laser | 18 eyes with open angle and normal IOP | 30 eyes with open angle and normal IOP | 1742 eyes during DRS study | 30 eyes with open angle and normal IOP | 36 eyes with normal IOP and open angle 4 eyes with closed angle and high IOP
|
Total 70 eyes
35eyes PASCAL 35 eyes conventional PRP |
| Immediately after laser | 14 patients with open angle and high IOP. 1 patient with open angle and normal IOP 3 patients with closed angle and high IOP
|
6 patients with open angle and high IOP 24 patients with open angle and normal IOP 6 patients with closed angle and high IOP 4 patients with open angle and IOP fall
|
Significant rise in IOP in both groups
>5 mmHg in 23/35(71.4%) in PASCAL,5/35(14.2%) in conventional at 1 hour >8mmHg in 22.8% in PASCAL group |
|||
| Hours later | Among 14 patients of open angle with high IOP, 5 developed angle closures.
|
10 patients developed angle closure and 20 patients develop narrow angle IOP in closed angle group: 10-27 mmHg and in narrow angle group: 20-29mmHg
|
Among 6 patients of open angle with high IOP, 1 patients developed angle
closure |
Significant rise in IOP in both groups >6mmHg in 23/35(71.4%) in PASCAL
5/35(14.2%) in conventional at 6 hour >8mmHg in 22.8% in PASCAL group |
||
| Months later | Significant decline in IOP of 3.1mmHg at 1month and of 2.2mmHg at 6months | No significant change in IOP | IOP came back to normal at day 1 and continued to be normal at 3 month and 6 months |
In our study, anterior chamber angle narrowing,along with an increase in ciliary body thickness and effusion in both groups were significant at day1. While the angle returned to baseline by 1 week, the increased ciliary body thickness continuedtill the end of our review, 3 months.
| variables | Yuki et al24
(1996) |
Gentile et al25(1996) | Zhang et al26(2001) | Birinci et al27(2006) | Present study |
| Before laser | 21 eyes with open angles | 39 eyes with open angles | 36eyes with open angles | 170 eyes with normal IOP and open angles | Total 70 eyes
35 in PASCAL 35 in conventional |
| Immediately after laser | No ciliary body effusion/detachment | No ciliary body effusion/detachment | No ciliary body effusion/detachment | Significantly elevated IOP at 1hour with shallowing of anterior chamber | |
| 3days later
|
19/21 eyes(90%) eyes showed ciliochoroidal detachment | 23/39 eyes(59%)showed ciliochoroidal effusion at day 1 | 29/36 eyes (80.6%)showed ciliochoroidal effusion and shallowing of anterior chamber depth with associated IOP rise | Normal IOP and anterior chamber depth | Narrowing in anterior chamber angle at day 1
27/70 eyes showed angle narrowing 12/35(34.2%)in PASCAL 15/35(42.8%)in conventional group at day 1 Increase in ciliary body thickness noted at day 1,more in conventional group 55/70 (78.5%) showed ciliary body effusion 20/35 (57.1%) eyes in PASCAL 35/35(100%) eyes in conventional group |
| 7 days later | Resolved Spontaneously | Reolved spontaneously in 12/23 eyes(52%) | Resolved spontaneously | Angle changes came back to normal
Ciliary body effusion continues to be there to some extent |
|
| 14 days later | Resolved in all eyes | Ciliary body effusion continued to be there
to some extent |
| variable | Lim C. et al28(2009) | Jongshin et al29(2012) | Jong et al30(2013) | Lee Eik et al31(2014) | Park et al32(2014) | Eren et al33(2014) | Filek et al34(2017) | Present study |
| Before laser | 94 eyes of normal healthy individuals
89 eyes DR PATIENTS with no PRP 37 eyes DR patients underwent PRP |
68 eyes studied retrospectively | 35 eyes studied prospectively | 35 eyes in PASCAL
49eyes control group |
105 eyes studied retrospectively
33 eyes PASCAL 34 eyes conventional PRP 38 eyes control |
58 treatment naïve eyes | 16 eyes and 8 eyes controls | Total 70 eyes
35 in PASCAL 35 in conventional |
| Result early period(months) | Eyes with PRP had thinner peripapillary RNFL | Peripapillary RNFL thickness slightly increased at 3months | Peripapillary RNFL thickness increased in early months post PRP | Peripapillary RNFL thickness increased at 2 months
Decreased at 6 months |
Peripapillary RNFL thickness showed no change in PASCAL
Peripapillary RNFL thickness decreased significantly at 6months in conventional group |
Peripapillary RNFL thickness increase noted at 3months,RNFl THICKNESS decreased at 6 months post PRP | Nonsignificant thickening of RNFL at 6 month | Nonsignificant thickening of RNFL at 3months |
| Later(years) | Statistically significant reductions at 2 years post PRP | RNFL thickness decreased significantly at 12 months post PRP | Peripapillary RNFL thickness decreased significantly in conventional group at 1 year | Recovered RNFL thickness at 24 months |
Our study concluded that PASCAL laser system is a safe and efficient method in treatment of PDR and severe NPDR, although not fully free of adverse effects. As shown in our study, patients can have an IOP spike just after PRP along with anterior chamber narrowing and ciliary body effusion at day 1 following PRP. As diabetic retinopathy patients can have POAG or PACG and diabetic neuropathy also, hence this spike in IOP and narrowing of angle can be dangerous in patients with preexisting glaucoma or compromised optic nerve function because of other causes and also with preexisting narrow angle. PRP in patients with compromised optic nerve function can lead to further deterioration of quality of vision. PRP can result in further narrowing in angle in patients with preexisting narrow angle and can predispose the patient to the risk of acute angle closure and further rise in IOP which can be detrimental. Hence we recommend to be vigilant before performing PRP in such patients. To divide the laser in 2 or more sittings rather then performing it in a single sitting. To prescribe an antiglaucoma medication after PRP in at risk patients, as to control the IOP spike.To record IOP after 1 hour of performing PRP.
The current PASCAL system is not designed for portability. Furthermore, it does not support endolaser delivery, which is needed intraoperatively. These aspects provide limitations to the PASCAL compared with the versatility of conventional laser systems. Nonetheless, from a surgeon’s outlook, the ability to reduce PRP time is a great advantage over past laser delivery systems. Combined with similar efficacy, decreased patient discomfort, and lesser collateral damage, this represents a significant enhancement in PRP treatments. It may be reasonable to conclude that PASCAL has ushered in a paradigm shift in PRP delivery systems.
There are 2 school of thoughts for intraocular pressure changes, one saying that IOP rises after PRP and another saying PRP leads to a decrease in IOP20,21,22. On anterior segment optical coherence tomography, angle narrowing and even episodes of acute angle closure have been observed in previous studies23,24,25 . Only a few studies has been done earlier for IOP and anterior chamber angle changes following panretinal photocoagulation using PASCAL , and these looked at only a few parameters. Therefore our study is novel, as we aimed for a comprehensive study to evaluate the effects of panretinal photocoagulation on IOP, anterior chamber angle, ciliary body thickness changes, RNFL and GCC changes following PASCAL and to compare these with conventional laser in diabetic retinopathy.
Key words: PASCAL photocoagulator, panretinal photocoagulation, proliferative diabetic retinopathy, conventional photocoagulation.
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Table 1 -Baseline parameters of two groups.
| Baseline Parameters | Conventional | Pascal | p value |
| IOP | 13.82+/-2.49mmHg | 14.7+/-2.87mmHg | 0.16 |
| CCT | 525.3+/-10.36mm | 524.3+/-17.12mm | 0.71 |
| AOD 500 | 0.359+/-0.11mm | 0.345+/-0.11mm | 0.58 |
| AOD 750 | 0.496+/-0.226mm | 0.412+/-0.134mm | 0.21 |
| TISA 500 | 0.152+/-0.05mm2 | 0.15+/-0.05mm2 | 0.88 |
| TISA 750 | 0.25+/-0.07mm2 | 0.243+/-0.06mm2 | 0.65 |
| ICA | 33.240+/-4.270 | 32.980+/-4.460 | 0.8 |
| CBT | 1.61+/-0.08mm | 1.59+/-0.07mm | 0.06 |
| IRT | 0.41+/-0.007 | 0.423+/-0.01 | 0.1 |
| RNFL | 84.45+/-4.31mm | 82.6+/-mm | 0.08 |
| GCC | 82.34+/-1.84 mm | 82.17+/-2.02mm | 0.71 |
Table 2: Comparison of IOP changes after PASCAL or Conventional laser PRP, from baseline over 3 months of review
| baseline | 1hour | 6hour | 1day | 1week | 4weeks | 8weeks | 12weeks | |
| conventional | 13.82+/-2.49 | 17.48+/-3 | 14.22+/-2.46 | 13.82+/-2.39 | 13.71+/-2.48 | 13.77+/-2.5 | 13.82+/-2.49 | 13.81+/-2.48 |
| PASCAL | 14.74+/-2.91 | 21.17+/-4.01 | 14.4+/2.82 | 13.82+/-2.07 | 13.77+/-1.86 | 13.82+/-1.9 | 14.11+/-2.5 | 13.82+/-2 |
| p-value(PASCAL vs conventional) | 0.16 | 0.00 | 0.00 | 0.78 | 0.91 | 0.63 | 0.77 | 0.8 |
Table 3-Changes in ASOCT and UBM parameters of the anterior chamber pre and post PRP in PASCAL and conventional laser treated groups.
| AOD 500 | baseline | 1hour | 1day | 1week | 4week | 12week |
| Conventional
|
0.359+/-0.11 | 0.406+/-0.11 | 0.309+/-0.10 | 0.344+/-0.1 | 0.357+/-0.12 | 0.357+/-0.12 |
| PASCAL | 0.345+/-0.11 | 0.388+/-0.11 | 0.289+/-0.1 | 0.334+/-0.1 | 0.345+/-0.11 | 0.345+/-0.11 |
| p-value | 0.58 | 0.52 | 0.42 | 0.7 | 0.67 | 0.67
|
| AOD 750
Conventional
|
0.496+/-0.22 | 0.546+/-0.26 | 0.438+/-0.19 | 0.48+/-0.21 | 0.49+/-0.21 | 0.49+/-0.21 |
| PASCAL | 0.412+/-0.13 | 0.511+/-0.2 | 0.383+/-0.12 | 0.377+/-0.14 | 0.415+/-0.14 | 0.41+/-0.14 |
| p-value | 0.2 | 0.89 | 0.03 | 0.09 | 0.23 | 0.23 |
| TISA 500
Conventional
|
0.152+/-0.05 | 0.188+/-0.05 | 0.122+/-0.05 | 0.145+/-0.05 | 0.152+/-0.06 | 0.152+/-0.06 |
| PASCAL | 0.15+/-0.05 | 0.17+/-0.06 | 0.097+/-0.03 | 0.136+/-0.04 | 0.151+/-0.05 | 0.151+/-0.05 |
| p-value | 0.88 | 0.21 | 0.04 | 0.5 | 0.92 | 0.92 |
| TISA 750
Conventional
|
0.25+/-0.07 | o.287+/-0.08 | 0.202+/-0.07 | 0.245+/-0.07 | 0.25+/-0.08 | 0.25+/-0.08 |
| PASCAL | 0.243+/-0.06 | 0.283+/-0.08 | 0.193+/-0.05 | 0.225+/-0.06 | 0.245+/-0.07 | 0.245+/-0.07 |
| p-value | 0.65 | 0.87 | 0.55 | 0.31 | 0.58 | 0.58 |
| Ciliary body thickness UBM
conventional |
Baseline
1.61+/-0.08 |
1Day
1.94+/-0.09 |
1week
1.63+/-0.08 |
4week
1.63+/-0.08 |
12weeks
1.63+/-0.08 |
| PASCAL | 1.59+/-0.07 | 1.76+/-0.1 | 1.58+/-0.08 | 1.58+/-0.08 | 1.58+/-0.08 |
| p-value | 0.06 | 0.00 | 0.02 | 0.02 | 0.02 |
| Iridocorneal angle UBM
conventional |
33.24+/-4.27 |
29.24+/-5.07 |
32.87+/-4.19 |
33.25+/-4.2 |
33.24+/-4.26 |
| PASCAL | 32.98+/-4.46 | 29.61+/-4.72 | 32.68+/-4.11 | 33.06+/-4.39 | 32.96+/-4.39 |
| p-value | 0.8 | 0.75 | 0.85 | 0.85 | 0.78 |
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