OF RETINAL NERVE FIBRE LAYER THICKNESS BY CIRRUS HD-OPTICAL COHERENCE TOMOGRAPHY IN EMMETROPIC, MYOPIC AND HYPEROPIC EYES”

Purpose : The purpose of our study is to compare the average peripapillary retinal nerve fibre layer thickness by cirrus HD-Optical coherence tomography in emmetropic, axial myopic and axial hyperopic cases. Methods The average as well as quadratic assessment of peripapillary Based on the histological studies, the peripapillary thickness follows pattern double at inferior and superior of the optic and thinnest at the nasal and temporal disc margins varies with the axial length of the evaluate of the optic nerve and retinal cross-sectional with approximately 2-3 mm penetration inside the tissue and micrometre scale of axial and transverse resolution for optic nerve and retina and anterior segment of the This high resolution OCT allows visualization of intra-retinal layers and correct measurement of retinal thickness, the RNFL.(4,5) OCT is a new imaging technology based on the laser interferometry principle. Comparison of OCT and histological images from prototype shown good correlation between real measurements of RNFL thickness and OCT estimates.(6) to many in early and like, retinopathy, central serous macular macular holes and epiretinal membrane.(6) Previous studies carried out with OCT technique revealed that axial length influences RNFL If axial length related ocular magnification not into RNFL thickness thins out as the eye elongates. the of glaucoma when eyes with different axial length are compared normative is with shorter axial RNFL Standard Deviation in of statistically significant (p= average and left eye RNFL Standard statistically (p= 0.000) Multiple comparisons were done between the by Bonferroni test. showed highly statistical significance with myopia values Hypermetropia showed highly statistical significance with myopia in all quadrants and average values hypermetropia showed statistical significance with emmetropia only statistical significant difference noted in between emmetropic and hyperopic groups, it showed significant difference only in right eye temporal quadrant and left eye nasal and superior quadrants.


ISSN: 2320-5407
Int. J. Adv. Res. 9(01), 62-71 63 is reduced to 10 µ here. (2) Based on the histological studies, the peripapillary RNFL thickness follows pattern of double hump whereby thickness is greatest at the inferior and superior poles of the optic disc and thinnest at the nasal and temporal disc margins and it varies with the axial length of the eye. (1,3) Optical coherence tomography (OCT) is a non-invasive technique that has been used extensively to evaluate pathologies of the optic nerve and retinal structure. This technique was first demonstrated in 1991 by Huang et al. (4) HD OCT provides crosssectional images with approximately 2-3 mm penetration inside the tissue and micrometre scale of axial and transverse resolution for optic nerve and retina and anterior segment of the eye. This high resolution OCT allows visualization of intra-retinal layers and correct measurement of retinal thickness, mainly the RNFL. (4,5) OCT is a new imaging technology based on the laser interferometry principle. Comparison of OCT and histological images from prototype devices shown good correlation between real measurements of RNFL thickness and OCT estimates.(6) 2 RNFL thickness measurement helps to detect many ocular diseases in early stages such as myopia, glaucoma and conditions like, diabetic retinopathy, central serous chorioretinopathy, macular edema, macular holes and epiretinal membrane. (6) Previous studies carried out with OCT technique revealed that axial length influences RNFL thickness. If axial length related ocular magnification is not taken into account, RNFL thickness thins out as the eye elongates. This value also helps in the diagnosis of glaucoma when eyes with different axial length are compared with the normative database. RNFL is thicker with shorter axial length. (7) Our study is aimed to assess whether axial length exerts any effect on the peripapillary RNFL thickness measurement performed by cirrus HD-OCT. We have analysed Average peripapillary RNFL thickness in 3 different groups of healthy emmetropic, hyperopic and myopic subjects.

Materials And Methods:-Patient Selection:
The study was performed at Santhiram Medical College & Hospital ,Nandyal, Andhra Pradesh,from October 2019 to March 2020. In this study,120 individuals in the age group of 10-50 years underwent evaluation of peripapillary retinal nerve fibre layer (RNFL) thickness using Spectral Domain OCT (Cirrus HD OCT). They were split into three different groups with 40 patients in each. Group 1 as emmetropia Group 2 as myopia >2.5 D and Group 3 as hyperopia >2.5 D In group 2 and group 3 subjects with astigmatism of > 1.5 D and with any other pathology or surgery were excluded from the study. 31

Procedure: Information and Screening:
The subjects were informed about the general procedure and the study both verbally and written form. Each subject signed an informed consent form on information of the study, see Annexure. Prior to the RNFL measurements a short history was taken. Dilated refraction was assessed by auto-refractometer based on their current glasses. OCT Measurements: All the subjects who fulfilled the inclusion criteria were subjected to the OCT, and the retinal thickness was measured. Peripapillary RNFL Thickness Measurement: RNFL thickness measurement was performed by Spectral Domain OCT in a mydriatic and cycloplegic state, by a single technician who was masked to subjects' clinical information. Scans were centred on the optic disc and scanning diameter of 3.5 mm obtained. Scans were repeated 3 times and assessed for signal strength and centration. Scans with poor signal strength quality and concentration were excluded. The RNFL thickness of each of the 4 quadrants and the average RNFL thickness were recorded in micrometres (µm).

Results:-
In our study, 240 eyes of 120 subjects underwent evaluation of peripapillary retinal nerve fibre layer thickness in the age group of 10-50 years in which 58 females and 62 males using Spectral Domain OCT. The quadrantic assessment of RNFL thickness in the 3 different groups followed ISNT rule with inferior quadrant showing the greatest thickness followed by the superior, nasal and temporal quadrants and the average RNFL thickness were assessed. Total of 120 patients were enrolled in this study, 40 each in the three arms namely emmetropia, myopia and hypermetropia. In these groups 58 (48.3%) were females and 62 (51.7%) were males. Based on age distribution, there are 12 individuals in 20 and below (10%), 45 in 21-30 years of age group(37.5%), 27 between 31-40 years of age group(22.5%),35 in 41-50 years of age group(29.2%), 1 above 50 years(0.8%).

Discusssion:-
Our study demonstrated that Average retinal nerve fibre layer thickness and RNFL thickness in all the 4 quadrants that is inferior, nasal, superior and temporal by cirrus HD OCT in emmetropia, myopia and hyperopia along the 3. Our study results done by ANOVA test shown that average and all the 4 quadrants RNFL thickness has statistically significant difference between all the 3 groups, emmetropia (p=0.000), myopia (p0.05).But hypermetropia showed statistical significance with emmetropia only in right eye temporal quadrant and left eye nasal and superior quadrants. This suggested that the RNFL thinning in the myopic group was due elongation of axial length and hyperopic group had a thicker RNFL in some quadrants as compared to those with emmetropia.

Conclusion:-
Our study concludes that axial length influences the peripapillary RNFL thickness mean average as well as of inferior, nasal, superior and temporal quadrants in emmetropic, myopic and hypermetropic group. When compared with emmetropia and hypermetropia, myopic group has statistically significant thinner RNFL thickness. But no 71 much statistical significant difference noted in between emmetropic and hyperopic groups, except it showed significant difference only in right eye temporal quadrant and left eye nasal and superior quadrants.