Effect of refractive errors/axial length on peripapillary retinal nerve fibre layer thickness (RNFL) measured by Topcon SD-OCT.

OBJECTIVE: To evaluate the effect of refractive error and axial length on peripapillary retinal nerve fibre layer thickness in myopic, hypermetropic and emmetropic eyes by Topcon spectral domain optical coherence tomography. METHODS: This cross-sectional study was conducted at the ophthalmology clinic of Shifa Foundation Falahee Clinic, Islamabad, Pakistan, from January to December 2016, and comprised eye patients including emmetropes, hypermetropes and myopes. All participants underwent detailed ophthalmic examination including axial lengths measurements, auto refraction andretinal nerve fibre layer thickness analysis. Retinal nerve fibre layer thickness was obtained from the peripapillary quadrants: temporal, superior, nasal and inferior and 12 sub-quadrants using Topcon spectral domain optical coherence tomography. Pearson correlation coefficients (r) were calculated to evaluate relationships between the retinal nerve fibre layer thickness and axial length before and after adjustment for ocular magnification by using Littmann's formula. RESULTS: Of the total 93 eyes of as many patients, 46(49.5%) were right eyes and 47(51.5%) left eyes. There were 35(37.6%) myopes, 29(31.2%) hypermetropes and 29(31.2%) emmetropes. Mean age was 30.45±7.86years. Mean axial length was 23.40±1.25mm.Mean retinal nerve fibre layer thickness after correction of magnification effect was 100.59±9.25 µm. Correlation analyses showed that the average retinal nerve fibre layer thickness and mean thickness of major superior and nasal quadrants and also in nasal, upper nasal, superonasal, inferior and inferonasal sub-quadrants had negative correlation with axial length. However, correction of the magnification effect by applying Littmann's formula eliminated the relationship between the two.. CONCLUSIONS: Retinal nerve fibre layer thickness measurements were found to vary with refractive status and axial length of the eye. Ocular magnification significantly affected the retinal nerve fibre layer thickness, and it should be considered in diagnosing glaucoma.

Mean Ocular Perfusion Pressure Effect During Pars Plana Vitrectomy on the Foveal Avascular Zone: A Pilot Study.

Purpose: To evaluate the effect of mean ocular perfusion pressure on the foveal avascular zone (FAZ) area in eyes with successful retinal detachment (RD) surgery. Methods: This prospective pilot fellow eye-controlled study measured the intraoperative mean ocular perfusion pressure in eyes having surgery for rhegmatogenous RD (RRD). Postoperatively, the FAZ area was measured; the change was calculated as the difference in the FAZ area between the operated eye and the contralateral control eye. Results: The study comprised 8 patients with a mean age (±SD) of 53.38 ± 13.92 years. The mean superficial FAZ area was not different between operated eyes and control eyes, while the deep FAZ area was significantly larger in operated eyes. There was a strong negative correlation between the mean ocular perfusion pressure and the change in the deep FAZ area (Spearman ρ, -0.73; P = .04); the correlation between the mean ocular perfusion pressure and the change in the superficial FAZ area was not significant (Spearman ρ, -0.24; P = .57). A significant linear regression was found between the mean ocular perfusion pressure and the change in the deep FAZ area (R2 = 0.388). The predicted enlargement of the deep FAZ area was 0.03 mm with every 1 mm Hg decrease in the mean ocular perfusion pressure. Conclusions: Lower intraoperative mean ocular perfusion pressure is associated with enlargement of the deep FAZ area in eyes having successful RRD surgery.

Analysis of retinal nerve fibre layer changes in anisometropic amblyopia by Heidelberg retina tomograph.

OBJECTIVE: To identify if anisometropic amblyopia is associated with changes in optic disk morphology. METHODS: The study comprised a total of 80 eyes recruited from Shifa Foundation Community Health Centre and the Pakistan Institute of Medical Sciences, Islamabad between May and October 2012. Anisometropic amblyopia was the only cause of disability (visual acuity > or = 6/12) in amblyopic eyes whereas normal eyes had a best corrected visual acuity of 6/6 and no morbidities. Patients with other causes of amblyopia, co-morbid ocular diseases, and in whom a good-quality image could not be obtained were excluded. Mean retinal nerve fiber layer thickness was analysed using Heidelberg retina tomograph. Analysis of frequency distribution, probability and regression were run on the data collected during the study using SPSS version 15.0. RESULTS: The mean age of the patients was 23.85 +/- 5.85 years. The retinal nerve fibre layer thickness ranged between 0.09 mm and 0.35 mm (mean: 0.23 mm +/- 0.07) in amblyopic eyes, and between 0.18 mm and 0.36 mm (mean: 0.25 mm +/- 0.05) in normal eyes. The difference was not statistically significant (p = 0.087). No association was found between the retinal nerve fiber layer thickness or the age and refractive error of patients. CONCLUSION: The optic disk does not appear to be the site of morphological changes in amblyopia.

Peripapillary Retinal Nerve Fiber Layer (RNFL) Thickness Measurements by Topcon SD-OCT in Myopic Patients.

OBJECTIVE: To evaluate the effect of low-to-moderate myopia on peripapillary retinal nerve fiber layer (RNFL) thickness measured by Topcon SD optical coherence tomography (OCT). STUDY DESIGN: Cross-sectional study. PLACE AND DURATION OF STUDY: Ophthalmology Department, Shifa Foundation Falahee Clinic, over a period of one year starting from June 2015. METHODOLOGY: A total of 43 eyes of 43 patients, having mild to moderate myopic refractive error, were enrolled in the study. Refractive error/spherical equivalent was calculated. RNFL thickness was obtained from all four peripapillary quadrants: temporal, superior, nasal, and inferior; and 12 sub-quadrants using Topcon SD OCT. Pearson correlation coefficients (r) were calculated to evaluate relationships between the RNFL thickness and spherical equivalent (SE) before and after adjustment for ocular magnification. RESULTS: The study included 51.2% females and 48.8% males. Mean age was 30.9 ±6.45 years. Mean axial length was 24.25 ±0.91 mm. Mean SE was -3.25 ±1.93 DS. Mean of average RNFL thickness (with Littmann's correction) was 97.28 ±8.15 µm. Correlation analysis among all subjects showed that the average, mean nasal quadrant, upper nasal, and inferonasal sub-quadrant RNFL thickness had positive correlation with spherical equivalent (r = 0.31, p = 0.045).However, correction of the magnification effect by applying Littmann formula eliminated this effect. CONCLUSION: In low-to-moderate myopia, RNFL measurements vary with refractive error of the eye. Since ocular magnification significantly affects the RNFL measurement, it should be considered in diagnosing glaucoma.

Central Corneal Thickness and its Relationship to Intra-Ocular and Epidmiological Determinants.

OBJECTIVE: To measure central corneal thickness in Pakistani population and determine its relationship to intra-ocular pressure, age, gender and ethnicity. STUDY DESIGN: Cross-sectional observation study. PLACE AND DURATION OF STUDY: Pakistan Institute of Medical Sciences, Islamabad, Pakistan, between December 2013 and February 2015. METHODOLOGY: The right eyes of 1000 cases (496 males and 504 females) were recruited for this study. Inclusion criteria were Pashtun or Punjabi ethnicity, intra-ocular pressure < 22 mmHg, gonioscopically open angles, cup-disk-ratio < 0.5, and age matched normal visual fields. Cases with prior ocular surgery, contact lens use, corneal pathologies, myopia or hypermetropia > ±3.0 diopters, astigmatism of > ±1.0 diopters were excluded. Central corneal thickness was measured using a TopCon non-contact specular microscope. Intra-ocular pressure was measured using Goldmann applanation tonometer. Frequency distribution, test of significance, and regression analysis was carried out using Statistical Package for Social Sciences version 20.0. RESULTS: Mean age was 47.31 ±11.78 years. Ethnic composition was 51.6% (n=516) Pashtun and 48.4% (n=484) Punjabi. The mean central corneal thickness was 503.96 (±12.47) µm, while the mean intra-ocular pressure was 15.61 (±2.68) mmHg. Regression analysis showed a significant association between central corneal thickness and intra-ocular pressure (p=0.00) and age (p=0.00). A±100 µchange in central corneal thickness was associated with change in IOPof ±3.30 mmHg, whereas central corneal thickness decreased by 0.12 µm per year. No significant association could be established between central corneal thickness and ethnicity (p=0.19). CONCLUSION: Central corneal thickness of the studied races was comparable to non-Caucasians which affects intra-ocular pressure measurements, and decreases with increasing age. No relationship was observed between central corneal thickness and ethnicity or gender.