Evaluation of retinal nerve fiber layer thickness parameters in myopic population using scanning laser polarimetry (GDxVCC).

INTRODUCTION: Myopia presents a significant challenge to the ophthalmologist as myopic discs are often large, tilted, with deep cups and have a thinner neuroretinal rim all of which may mimic glaucomatous optic nerve head changes causing an error in diagnosis. OBJECTIVE: To evaluate the retinal fiber layer (RNFL) thickness in low, moderate and high myopia using scanning laser polarimetry with variable corneal compensation (GDxVCC). SUBJECTS AND METHODS: One hundred eyes of 100 emmetropes, 30 eyes of low myopes (0 to - 4 D spherical equivalent(SE), 45 eyes with moderate myopia (- 4 to - 8D SE), and 30 eyes with high myopia (- 8 to - 15D SE) were subjected to retinal nerve fiber layer assessment using the scanning laser polarimetry (GDxVCC) in all subjects using the standard protocol. Subjects with IOP > 21 mm Hg, optic nerve head or visual field changes suggestive of glaucoma were excluded from the study. The major outcome parameters were temporal-superior-nasal-inferiortemporal (TSNIT) average, the superior and inferior average and the nerve fibre indicator (NFI). RESULTS: The TSNIT average (p = 0.009), superior (p = 0.001) and inferior average (p = 0.008) were significantly lower; the NFI was higher (P less than 0.001) in moderate myopes as compared to that in emmetropes. In high myopia the RNFL showed supranormal values; the TSNIT average, superior and inferior average was significantly higher(p less than 0.001) as compared to that in emmetropes. CONCLUSION: The RNFL measurements on scanning laser polarimetry are affected by the myopic refractive error. Moderate myopes show a significant thinning of the RNFL. In high myopia due to peripapillary chorioretinal atrophy and contribution of scleral birefringence, the RNFL values are abnormally high. These findings need to be taken into account while assessing and monitoring glaucoma damage in moderate to high myopes on GDxVCC.

Trypan blue staining of filtering bleb in eyes with operate trabeculectomy.

OBJECTIVE: To report the use of trypan blue staining of the filtering bleb to assess its functional status in eyes undergoing phacoemulsification after trabeculectomy. SUBJECTS AND METHODS: This retrospective study was conducted at a tertiary eye care centre in North India and studied 33 eyes of 33 patients ( with previously operated trabeculectomy), who underwent phacoemulsification. Trypan blue dye (0.06%) was used to stain the anterior capsule. After completion of phacoemulsification, the staining of the trabeculectomy bleb was noted as diffuse, patchy, minimal or no staining. RESULTS: Of the 33 eyes, 13 had diffuse staining (39.4%, mean IOP = 9.3 ± 2.2 mm Hg), 7 (21.2%, mean IOP= 15.5 ± 1.8 mm Hg) had patchy staining, 4 had minimal staining (12.1%, mean IOP= 17.5 ± 0.5mm Hg) and nine (27.3%, mean IOP= 19.3 ± 1.6 mm Hg) had no staining. These staining patterns were labeled as groups 1 - 4 respectively. Statistical analysis showed that the difference between the IOPs in Group 1 - 2 and between Group 2 - 3 was not significant statistically (p=0.682 and 0.665 respectively). However the differences between the IOPs between Groups 1 - 3, 1 - 4, 2 - 4, and 3 - 4 were found to be highly significant statistically (p less than 0.0005). CONCLUSIONS: Trypan blue dye can be used to test the amount of sub conjunctival filtration in eyes undergoing phacoemulsification cataract surgery.