|Year : 2013 | Volume
| Issue : 2 | Page : 73-78
Evaluation of corneal endothelium before and after neodymium : Yttrium-aluminium-garnet laser capsulotomy in posterior capsular opacification
Neha Rajappa, Abhay Lune, OK Radhakrishnan, Renu Magdum, Pallavi Patil, Rahul Mehta
Department of Ophthalmology, Dr. D. Y. Patil Medical College, Hospital and Research Centre, Pimpri, Pune, Maharashtra, India
|Date of Web Publication||10-Jan-2014|
1101, A-wing, Monarch, Ashar Residency, Pokhran Road-2, Thane (West) - 400 607, Maharashtra
Aim: The aim of this study is to evaluate the corneal endothelial changes before and after neodymium:yttrium-aluminium-garnet (Nd:YAG) laser posterior capsulotomy in patients with posterior capsular opacification (PCO) among adults. Materials and Methods: This prospective non-comparative study was carried out in 200 eyes of 200 adult patients with clinically diagnosed PCO. Eyes were later subjected to Nd:YAG laser capsulotomy and followed up at 1-12 weeks to evaluate the damage caused by laser on the corneal endothelium. Computerized morphometry was used to evaluate the central corneal thickness, size, shape and cellular density, coefficient of variation and hexagonality of the endothelial cells using non-contact specular microscopy before and after laser capsulotomy. Data was analyzed using Chi-square and t-test and P < 0.05 were considered significant. Results: Endothelial cell density (ECD) varied from 1659 to 2792 cells/mm 2 with a mean of 2298.7 cells/mm 2 before laser treatment. At 1 week, the mean ECD was 2178.1 cells/mm 2 (P < 0.0001) and 12 weeks was 2121.3 cells/mm 2 (P < 0.0001). The difference between pre-laser ECD and ECD at 1-12 week was 120.6 cells/mm 2 and 177.4 cells/mm 2 (7.78%) respectively which was found to be highly significant. Hexagonality of corneal cells varied from 49% to 84% with a mean of 72.22% pre-laser. At 1 week, hexagonality was 71.42% (P < 0.005) and at 12 weeks was 70.22% (P < 0.0001). The difference was clinically significant. 90% patients had two or more than two Snellen's line visual improvement. Conclusion: In our study, although there was a dramatic improvement in visual acuity after laser capsulotomy, we found a significant reduction of ECD. Although Nd:YAG laser capsulotomy presents the advantage of being non-invasive and effective method to treat PCO, the corneal endothelium may be damaged by laser radiation.
Keywords: Endothelial cell density, hexagonality, neodymium:yttrium-aluminium-garnetlaser, polymegathism, posterior capsular opacification, specular microscopy
|How to cite this article:|
Rajappa N, Lune A, Radhakrishnan O K, Magdum R, Patil P, Mehta R. Evaluation of corneal endothelium before and after neodymium : Yttrium-aluminium-garnet laser capsulotomy in posterior capsular opacification. Sudanese J Ophthalmol 2013;5:73-8
|How to cite this URL:|
Rajappa N, Lune A, Radhakrishnan O K, Magdum R, Patil P, Mehta R. Evaluation of corneal endothelium before and after neodymium : Yttrium-aluminium-garnet laser capsulotomy in posterior capsular opacification. Sudanese J Ophthalmol [serial online] 2013 [cited 2019 May 21];5:73-8. Available from: http://www.sjopthal.net/text.asp?2013/5/2/73/124831
| Introduction|| |
A major complication of cataract surgery is posterior capsular opacification (PCO), a condition, which develops months or years after successful cataract surgery. The time from surgery to visually significant opacification varies from months to years. , Sinskey and Cain  reported that 43% of their patients developed PCO from 3 months to 4 years. Emery et al.  found opacification in 28% of their patients within 2-3 years of follow-up. PCO is a major problem in pediatric cataract where the incidence approaches 100% between 2 months and 5 years after the initial surgery. Opacification of the posterior capsule can lead to clinically significant reduction in visual acuity, impaired contrast sensitivity, glare disability and monocular diplopia.
For treating PCO, neodymium:yttrium-aluminium-garnet (Nd:YAG)laser has been proven to be a valuable treatment modality. Although Nd:YAG laser capsulotomy presents the advantage of being non-invasive and effective method to treat PCO, corneal endothelium may be damaged by laser induced plasma formation, by laser radiation or by the shock wave. In order to evaluate this damage done by laser, we studied the corneal endothelium before and after Nd:YAG laser capsulotomy in adults.
| Materials and Methods|| |
This prospective non-comparative study was carried out in 200 eyes of 200 patients (92 male and 108 female) aged between 50 and 75 years, who attended the out-patient department between July 2011 and September 2012.
The details of the surgical procedure and the type of intraocular lens (IOL) implanted were not available as they were operated for cataract by different surgeons within and outside the hospital. The mean time interval between cataract surgery and Nd:YAG laser posterior capsulotomy was 2.5 year (range 1-4 years). All patients with PCO as diagnosed on slit lamp were included. Exclusion criteria included patients with significant corneal pathology, retinal pathology, pseudoexfoliation syndrome, recurrent iridocyclitis, traumatic cataract, primary and secondary glaucoma, diabetes mellitus and patients below 15 years of age.
All patients were evaluated before undergoing laser capsulotomy to confirm that the visual loss was due to PCO. Following protocols were done in each case prior to doing posterior capsulotomy, which included: Visual acuity, best corrected visual acuity, intraocular pressure (IOP) using applanation tonometer, slit lamp examination, fundus examination and specular microscopy using non-contact SP-3000P. Permission from ethics committee was taken. Informed consent was taken prior to investigation and treatment procedures.
Specular microscopy was performed using a non-contact specular microscope Topcon SP-3000P. Fixed frame analysis method was used to capture the central area of the cornea.
Wider auto alignment simplifies the capturing procedure. After positioning the patient, the central part of the cornea was focused. The auto tracking system then takes over an area of 8 mm × 8 mm with precise focusing and centering obtained automatically. The captured image was then transferred to the computer where the cell count software provided a highly precise analysis of the endothelial cell layer.
Computerized morphometry was used to evaluate the minimum, maximum and average endothelial cell area (they give the range of variation in cell size), standard deviation (SD) of the endothelial cell size from the mean (is a measure of polymegathism); coefficient of variation (CV), endothelial cell density (ECD) and hexagonality of cells. Outcome (dependent) variables for this study were corneal ECD, CV and percentage of hexagonal cells. Averages of parameters were used for the analysis. This specular microscope was calibrated so that when the endothelium is in focus, the thickness of the cornea automatically gets displayed digitally. Data was analyzed using Chi-square and t-test and P < 0.05 were considered to be significant.
After performing pre-laser assessment, patients were subjected to laser treatment. Before treatment 1% tropicamide eye drops were instilled to dilate the pupil and the cornea was anaesthetized with topical 0.5% proparacaine hydrochloride. Patients were then subjected to Q-switched Nd:YAG laser capsulotomy in the affected eye after measuring the IOP. Nd:YAG capsulotomy was performed on a slit lamp equipped with a YAG laser, with patient in a seated position. A Q-switched laser produces a series of single pulses that lasts for 12-20 nanoseconds. Because Nd:YAG laser is invisible, helium-neon focus beam was used for accurate aiming. All procedures were performed with an energy level of 3.0 mJ. The usual strategy was to create a cruciate opening, beginning superiorly near the 12 O'clock position and progressing downward toward 6 O'clock position. Unless a wide opening has already developed, shots are then placed at the edge of the capsule opening, progressing laterally toward the 3 and 9 O'clock positions. If any capsular flaps remain in the pupillary space, the laser is fired specifically at the flaps to cut them and cause them to retract and fall back to the periphery.
Post Nd:YAG laser posterior capsulotomy, all patients were administered topical steroids (eyedrop prednisolone 1%) four times daily for a week followed by two times daily for the 2 nd week, topical anti-inflammatory (eyedrop flurbiprofen) thrice a day for 2 weeks and topical timolol (0.5%) twice a day for a week. Post laser, patients were followed-up at 1-12 weeks for complete ocular examination and were looked for any incidence of iritis, hyphema, aqueous flare, vitritis, rise in IOP, retinal detachment and cystoid macular edema. Post laser, patients were reviewed for assessment of best-corrected visual acuity at 1 week.
| Results|| |
Corneal endothelium of 200 eyes of 200 patients (Male 92, Female 108) aged 50-75 years were evaluated before and after Nd:YAG laser capsulotomy. Out of 200 eyes, 144 eyes had Elschnig's type of PCO whereas the remaining 56 eyes had fibrotic type.
Energy Levels for the Type of PCO
The mean energy required for Elschnig's PCO was 51.33 mJ and that for fibrous type was 63.43 mJ as shown in [Table 1]. Elschnig's PCO being thinner required lower energy for capsulotomy as compared to the thicker fibrous capsule.
Visual Acuity Outcome
Pre-laser majority (58%) of patients had vision ranging from 20/60 to 20/40. There were 24 patients who had good vision (20/30-20/20) prior to laser, but had complaints of glare. Post laser at 1 week, there was marked an improvement of vision in most cases. There were 144 cases (72%) who had visual acuity of 20/30-20/20 after capsulotomy [Table 2]. There were four patients who had a vision below 20/80 and it may be contributed to the fact that they had a thick fibrotic PCO. During laser treatment, four patients developed IOL pitting but did not have any effect on the quality of vision [Figure 1]. It is evident in our study that there was a dramatic improvement in visual acuity (unaided) after laser capsulotomy.
|Figure 1: Visual acuity wise distribution of cases at pre-laser, 1 week and 12 weeks in the study group|
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|Table 2: Visual acuity (unaided) distribution of cases at pre-laser, 1 week and 12 weeks in the study group |
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ECD varied from 1659-2792 cells/mm 2 with a mean of 2298.7 cells/mm 2 before laser treatment. At 1 week, mean ECD was 2178.1 cells/mm 2 (P < 0.0001) and at 12 weeks was found to be 2121.3 cells/mm 2 (P < 0.0001). The difference between pre-laser ECD and ECD at 1-12 weeks was 120.6 cells/mm 2 and 177.4 cells/mm 2 (7.78%) respectively [Table 3]. There was a significant difference in ECD before and after laser treatment [Figure 2].
|Figure 2: Comparison of cell density pre-laser, at 1 week and 12 weeks in the study group|
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|Table 3: Comparison of CD at pre-laser, 1 week and 12 weeks in the study group |
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In this study, the CV pre-laser was 0.337, at 1 week was 0.343 (P > 0.05) and at 12 weeks was 0.345 (P > 0.05) which was not clinically significant.
Hexagonality of corneal cells varied from 49% to 84% with a mean of 72.22% pre-laser. At 1 week, hexagonality was 71.42% (P < 0.005) and at 12 weeks was 70.22% (P < 0.0001), which was clinically significant [Table 4].
|Table 4: Comparison of hexagonal cells at pre-laser, 1 week and 12 weeks in study groups |
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The mean central corneal thickness before laser was 484.82 μm, at 1 week were 480.78 μm and at 12 weeks was found to be 481.02 μm, which was not significant (P > 0.05).
| Discussion|| |
PCO is the most common complication after ECCE surgery. It causes a reduction in visual acuity and contrast sensitivity by obstructing the view or by scattering the light that is perceived by patients as glare. It also decreases the field of view during therapeutic and diagnostic procedures and also causes uniocular diplopia.
Prior to the development of Nd:YAG laser, PCO was managed only by surgical capsulotomy. Nd:YAG laser capsulotomy introduced a technique for non-invasive, effective and relatively safe procedure. With the explosive nature of Nd:YAG photodisruption and the post plasma particulate dispersion throughout the anterior chamber borne in mind, the specular microscopic changes suggest a high velocity impact injury to the endothelium with maximal damage in the center of the lesion and graduated centrifugal changes.
Before 1970, the corneal endothelium was studied at high magnification only in vitro.  The development of clinical specular microscope , has made qualitative and quantitative in vivo evaluation of corneal endothelium possible.
In our study of 200 cases, the mean time interval between cataract surgery and Nd:YAG laser posterior capsulotomy was 2.5 years (range 1-4 years). Most patients presented with the chief complaint of diminution of vision 2-3 years after successful cataract surgery. In a study by Hassan et al.  the time interval between cataract surgery and PCO was reported as 2.49 years. The time of onset of PCO from the time of surgery varies. The frequency with which Nd:YAG laser capsulotomy is performed also varies, reported in the range of 3% to 53% within 3 years time. 
While applying laser, energy required depends upon the type of PCO. In our study, 144 eyes had Elschnig's type of PCO, whereas 56 eyes had fibrotic type. Nd:YAG capsulotomy was performed in all eyes irrespective of the type of PCO. The mean energy required for Elschnig's PCO was 51.33 mJ and that for fibrous type was 63.43 mJ. Compared with Elschnig's type of PCO, fibrous type is thicker and required additional number of laser shots to break the capsule.
It is evident from our study that there was a dramatic improvement in visual acuity after laser capsulotomy. Nd:YAG laser was effective in achieving a clear pupillary opening in every case. Nearly 90% patients had two or more than two snellen's line visual improvement. The visual improvement correlated with the findings of other studies. Aron-Rosa et al.  reported an immediate improvement in visual acuity in 94% of cases treated by capsulotomy. Terry et al.  showed improvement by one or more snellen acuity lines in 92% of patients treated. In another study by Hossain et al.,  visual outcome of 500 patients before and after capsulotomy was compared and 80% individuals showed improved visual acuity of ≥6/12.
Jones et al.  determined the repeatability of the Konan Robo non-contact specular microscope by capturing 36 images of each eye from one subject during a 4 month period. An assumption was made that the endothelial cell morphology does not significantly change during the 4 month period. The mean (±SD) cell density for the right eye was 2545 ± 45 cells/mm 2 . Since 99.7% of a normally distributed population is within 3 SDs, then the range of samples is 2680-2410 cells/mm 2 (±5.3%). The mean cell density for the left eye was 2600 ± 41 cells/mm 2 with 99.7% of the samples within 2723-2477 cells/mm 2 (±4.7%). The high level of repeatability reflects the low polymegathism in patients at 0.27-0.28 and the skill of the technician.
In our study, ECD varied from 1659 to 2792 cells/mm 2 with a mean of 2298.7 cells/mm 2 before laser treatment. At 1 week, the mean ECD was 2178.1 cells/mm 2 (P < 0.0001) and at 12 weeks was 2121.3 cells/mm 2 (P < 0.0001). The difference between pre-laser ECD and at 1-12 weeks was 120.6 cells/mm 2 and 177.4 cells/mm 2 (7.78%) respectively. The difference was found to be highly significant. In a similar study by Slomovic et al.,  the central corneal endothelial cell densities in 39 eyes before and after Q-switched Nd:YAG laser posterior capsulotomy was determined. The mean pre-laser endothelial cell count was 1.840 cells/mm 2 and post laser endothelial cell count was 1.798 cells/mm 2 . The difference was 42 cells/mm 2 (2.3% cell loss). The authors found no significant correlation between the central corneal endothelial cell loss before and after laser capsulotomy. In another study  corneal endothelium was analyzed in 33 patients (17 aphakic and 16 pseudophakic). The energy used for the impact was 2.6 ± 0.7 mJ and the total energy delivered was 110 ± 80 mJ. The cellular loss in aphakic patients was 8.1% on the third day and 5.9% by 3 rd month. In the pseudophakic group, cellular loss was 6.5% on the third day and 7.3% by the 3 rd month. The authors found a significant correlation between the endothelial cell loss and the total energy delivered.
In our study, the CV at baseline was 0.337, at 1 week was 0.343 (P > 0.05) and at 12 weeks was 0.345 (P > 0.05). We did not find any significant difference. Hexagonality is the predominant cell shape in the normal endothelium; thus deviations in the percentage of cells, which are hexagonal, can be used as an index of cell shape variation (pleomorphism). Hexagonality of corneal cells varied from 49% to 84% with a mean of 72.22% pre-laser. At 1 week, it was 71.42% (P < 0.005) and at 12 weeks was 70.22% (P < 0.0001) which was found to be clinically significant. The mean central corneal thickness before laser was 484.82 μm, at 1 week was 480.78 μm and at 12 weeks was found to be 481.02 μm, which was not significant.
The variation in the absolute number of cells lost may be attributable to several factors like target tissue/endothelium distance, the nature of the tissue being disrupted, differences in delivery of the laser energy (e.g., number of bursts, the number of pulses per burst, mode of delivery) and quantity of energy.
Though Nd:YAG laser capsulotomy is cheap, effective and safe procedure, it is not free of complications. During laser treatment, four patients developed IOL pitting, which did not affect their visual acuity. Hassan et al.  noted high incidence of 19.8% IOL pitting in 86 eyes. Pitting usually is not visually significant; although rarely the damage may cause sufficient glare and image degradation that the damaged IOL must be explanted. The damage threshold is lowest for silicone, intermediate for PMMA and highest for acrylic materials. , Several steps can be employed to minimize IOL damage, including using the lowest possible energy settings, stabilizing the eye with a contact lens, beginning treatment in areas of capsule-IOL separation, and in some cases focusing in the anterior vitreous and allowing the anterior radiation of the shockwave to rupture the capsule.
A transient rise in IOP after Nd:YAG laser capsulotomy has been well-documented. In a study done on 66 patients, Slomovic and Parrish  found that 55% patients had significantly raised IOP following YAG laser therapy. In another cross-sectional study conducted on 118 Nd:YAG posterior capsulotomy procedure, the authors found a significant rise in IOP one hour after laser capsulotomy in aphakic group than in pseudophakic group (8.2 mmHg and 3.5 mmHg) respectively.  However, Shani et al.  could not find any elevation of IOP in their study and postulated that healthy pseudophakic eyes do not generally show elevation of IOP. Hu et al.,  in their 3 month follow-up study, also did not find any persistent rise in IOP. Contrary to reports, we did not document any rise in IOP. It may be due to the fact that all patients were treated with topical timolol post laser for a week. Even during the 12 th week follow-up we did not document rise of IOP in any of our patients.
| Conclusion|| |
PCO is the most common complication of cataract surgery. In recent years, several advances and research has been done to prevent PCO by improving the surgical techniques, better IOL materials and design, use of therapeutic drugs. Nd:YAG capsulotomy has proved to be the most effective method to treat PCO as it is safe, non-invasive, economical OPD procedure. Though Nd:YAG laser capsulotomy is considered safe, it also carries a low risk of complication.
Majority of eyes that receive Nd:YAG laser for posterior capsulotomy have had undergone previous surgery. Therefore, the additional cell loss associated with laser is less tolerated by many and over the due period of time, may lead to corneal decompensation as a result of normal age related cell loss. While applying laser, care should be taken not to damage the surrounding structures like the IOL, vitreous, retina, iris and cornea. Furthermore, the energy levels should be kept minimum.
In our study, there was a visual improvement in 90% of cases. There was a significant loss of ECD after the laser procedure. The expected complications of Nd:YAG laser therapy was very minimal in our study when compared to other studies. The procedure is easy and visual recovery is rapid as compared to the invasive surgical capsulotomy.
To conclude, our results suggest that though ND:YAG laser capsulotomy is a safe procedure, it may pose a long-term hazard to the corneal endothelium.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]