FREQUENCY OF INTRA OCULAR PRESSURE CHANGE AFTER LOW ENERGY AND HIGH ENERGY ND: YAG LASER POSTERIOR CAPSULOTOMY.
Objective: To compare frequency of rise in Intra Ocular Pressure (IOP) in patients undergoing low energy and high energy Nd: YAG laser posterior capsulotomy.
Study Design: Comparative, cross-sectional study.
Place and Duration of Study: Armed Forces Institute of Ophthalmology (AFIO), Rawalpindi from January 2013 to August 2013.
Material and Methods: One hundred and twenty patients fulfilling the inclusion criteria were enrolled in the study. Base line IOP was measured with the help of Goldman applanation tonometer. After dilating pupil, Nd: YAG laser posterior capsulotomy was performed, using minimum possible pulses of Nd: YAG laser. The total amount of energy used in the procedure was recorded. IOP was measured 4 hours after the procedure. Post laser frequency of change in IOP (5 mm of Hg from baseline) was calculated in low energy and high energy groups. Chi square test was applied to compare the frequency of raised IOP in both groups.
Results: Raised IOP was noted in 33 (27.50%) cases and this was more common in high energy group occurring in 22 (46.8 % ) as compared to low energy group 11 ( 15.1 % ).The p-value was found to be 50 (n=47)###Low <50 ( n=73)
Pre-laser IOP###16.57 +- 1.65###17.18 +- 1.65###0.053
Post-laser IOP###21.62 +- 4.36###19.21 +- 3.21###0.001
Energy used###63.91 +- 9.60###44.04 +- 3.67###<0.001
Table-II: IOP raised or not raised energy cross tabulation.
###IOP raised or not###Total
The data were collected using a predefined proforma. Samples were selected from all the patients who underwent Nd: YAG laser capsulotomy. All the confounding variables were recognized during the study and were excluded through exclusion criteria.
One drop of proparacaine hydrochloride was used for topical anesthesia. Base line IOP was measured by Goldman applanation tonometer. Pupil was dilated with 1% tropicamide eye drops.
An opening of 3-4 mm was made in the posterior capsule, using minimum possible pulses of Nd: YAG laser with the help of Abraham capsulotomy lens. Total amount of energy used during the procedure was recorded, as viewed on the control display panel of Nd: YAG laser delivery system.
Two groups were made, low energy group, when energy used was <50 mJ and high energy group, when energy used was more than 50 mJ.
IOP was measured 4 hours following the procedure and was considered raised if more than 5 mm of Hg above baseline.
Age and gender status of the patients was also noted.
Data were analyzed by using SPSS version 13.0. Quantitative data like age, IOP, IOP in low and high energy Nd:YAG laser levels were presented by mean +- SD. Qualitative variables like gender, frequency and percentage of raised IOP and IOP in low and high energy Nd:YAG laser groups were also presented. Chi-square test was used to compare frequency of raised IOP in low and high energy groups.
Out of 120 cases, 64 (53.3%) were male and 56 (46.3%) were female. There were 28 (59.6%) males and 19 (40.4%) females in high energy group and 36 (49.3%) males and 37 (50.7%) females in low energy group. Mean age +- SD was 57.88 +- 6.01 years (Range 45-74 years). Mean age in high energy group was 57.34 +- 6.20 years (Range 45-70 years), and in low energy group was 58.22 +- 5.90 years (Range 46-74 years).
Both the high energy and low energy groups had similar mean pre laser IOP (p=0.053). Mean post laser IOP in high energy group was 21.62 +- 4.36 mm of Hg and in low energy group it was 19.21 +- 3.21 mm of Hg (p=0.001) Out of total 120 patients raised IOP was noted in 33 (27.5%) cases and IOP remained normal in 87 (72.5%) cases. In low energy group, raised IOP was noted in 11 out of 73 (15.1%) cases where as In high energy group, raised IOP was noted in 22 out of 47( 46.8%) cases.
Chi square test was applied that showed p-value0.001). This showed a higher frequency of raised IOP after high energy Nd: YAG laser posterior capsulotomy that is statistically significant.
PCO has a profound impact on the patient's life by causing social and economic burden. It also affects the daily routine life by reducing visual acuity and increasing the glare. Various surgical techniques have been devised to delay the incidence of PCO but still there are no conclusive results to halt the development of PCO.
Since the advent of Nd: YAG laser in 1981, its applications have ranged remarkably in various medical fields. It is widely accepted in the management of PCO among the surgeons as well as the patients, due to its non invasive approach and being outdoor procedure8.
Although it is the most effective treatment modality for the management of PCO, still it is not without complications. One of the important complications is raised IOP. Transient rise of IOP after Nd: YAG laser capsulotomy has been reported and well documented in literature and is 0.5-3 %9. These studies lack energy calculation and published results in general at all energy levels. Immediate rise of IOP after the procedure is due to absence of posterior chamber IOL and use of high energy Nd: YAG laser that resulted in prolapsed vitreous.
Raised IOP should be anticipated and managed accordingly with Goldman applanation tonometer which is a gold standard diagnostic tool10.
Various studies have proved that IOP was raised after the Nd: YAG laser posterior capsulotomy. Slomovic and Parrish found that 55% of patients had significantly raised IOP following YAG lasertherapy11. Flohr showed similar pattern of IOP rise that is similar to the results as depicted in our study12.
Ladas and colleagues studied 210 patients who underwent Nd: YAG laser capsulotomy. One group was giventopical 2% dorzolamide, second was given oral acetazolamide and the third group received no medicines prior to capsulotomy. Latter group experienced IOP higher than 30 mmHg in 15.7% cases after laser capsulotomy13. In this study the percentage of raised IOP is slightly <the other studies that are mentioned previously.
In our setup Waseem MA demonstrated elevation in IOP in 53 out of 148 (35.81%) cases6. Burq MA's study showed that raised IOP occurred in 48 out of 104 (46.2%) cases after Nd: YAG laser capsulotomy7. The results are almost similar in both studies.
In comparison to the above mentioned studies, our study showed the rise in IOP in 33 out of total 120 (27.5%) cases and IOP remained normal in 87 (72.5%) cases being slightly less in percentage than the previously mentioned studies.
Our study also showed the relationship of raised IOP with the amount of energy delivered during Nd: YAG laser posterior capsulotomy and found a positive relationship. Channel and Beckman also showed that raised IOP was associated with increased laser energy used during Nd: YAG laser capsulotomy14. In our population, a study by Waseem MA showed raised IOP in 21 out of 35 (60%) patients in high energy group as compared to raised IOP in 32 out of 113 (28.32%) patients in low energy group. In our study raised IOP was noted in 22 (46.8%) cases in high energy group as compared to 11 (15.1%) cases in low energy group. Both studies showed a strong positive association between the high amount of energy used and frequency of raised IOP.
Another important aspect that should be kept in mind is the habit of late presentation in our population due to socio-economic reasons. This leads to thick posterior capsules with marked reduction in visual acuity and profound glare at presentation. Thick posterior capsules require higher amount of laser energy as compared to thin capsule when patient present early. In these cases technique of ND: YAG laser capsulotomy is important that can reduce the amount of laser energy required for the procedure.
Although our study showed that frequency of raised IOP is strongly associated with high energy Nd: YAG laser posterior capsulotomy but it could not determine the exact mechanism of this relationship. It may be due to the acoustic shock wave generated by high energy laser triggering the release of inflammatory mediators that can alter the aqueous and trabecular dynamics resulting in raised IOP. Moreover this study could not compare the results of different studies due to different surgical techniques used to delay the incidence of PCO formation, including IOL material and design.
The results suggested that high energy levels used during Nd: YAG laser posterior capsulotomy had significantly more chances of raised IOP.
It is recommended that each patient undergoing Nd: YAG laser capsulotomy should receive minimum amount of energy and patient should be followed up for rise in IOP and managed accordingly.
CONFLICT OF INTEREST
This study has no conflict of interest to declare by any author.
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|Publication:||Pakistan Armed Forces Medical Journal|
|Date:||Oct 31, 2016|
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