Effect of phacoemulsification on measurement of retinal nerve fiber layer and optic nerve head parameters using spectral-domain-optical coherence tomography.

Abstract

PURPOSE:The purpose of this study is to determine the effect of phacoemulsification cataract extraction on measurement of retinal nerve fiber layer and optic nerve head parameters using spectral domain optical coherence tomography.MATERIAL AND METHODS:A prospective, hospital-based study of 100 patients of 40 years of age and above, with no other ocular morbidity except cataract and planned for phacoemulsification with IOL implantation (SN60WF) at a tertiary centre at AIIMS, New Delhi, India. All patients underwent imaging with Cirrus SD-OCT model 400 and the optic disc cube 200x200 protocol at baseline and at 1 month follow up. Paired sample t-test was used to compare the RNFL parameters and ONH parameters.RESULTS:The mean age of subjects was 56.6 ± 12.3 years (70 males, 30 females). The average RNFL increased from 92.6 ± 5.4 μm to 101.3 ± 5.6 μm after phacoemulsification, an increase of 9% (P = 0.003) and the signal strength increased from 5.6 ± 0.5 to 7.6 ± 0.7, increasing by 35.7% (P = 0.004). There was a significant increase in the disc area (P = 0.004) and rim area (P = 0.004) but no significant change in vertical cup-disc ratio (P = 0.45) or average cup-disc ratio (P = 0.075). The quadrant-wise RNFL thickness increase in inferior, superior, nasal, and temporal quadrants was 12.6% (P = 0.001), 10% (P = 0.001), 5.6% (P = 0.001), and 3.2% (P = 0.001), respectively. The change in RNFL thickness was maximum in posterior subcapsular cataract (P = 0.001) followed by cortical (P = 0.001) and nuclear (P = 0.001) subtypes.CONCLUSIONS:A significant increase in RNFL thickness and signal strength was observed after cataract surgery using SD-OCT. The maximum change in RNFL thickness was in the inferior quadrant, where RNFL thinning is a significant predictor of glaucoma progression. The posterior subcapsular cataract interfered with RNFL measurement maximally due to its density and proximity to nodal point. After the cataract surgery, a new baseline needs to be established by obtaining fresh OCT images for assessing the longitudinal follow-up of a glaucoma patient.