Brijesh Patil1, Anupama C Shetgar2, and Divya Teja V3*
1MS, Professor, Department of Ophthalmology, S. Nijalingappa Medical College and HSK Hospital, Bagalkot, Karnataka, India
2MS, Associate Professor, Department of Ophthalmology, S. Nijalingappa Medical College and HSK Hospital, Bagalkot, Karnataka, India
32nd DOMS, S. Nijalingappa, Medical College and HSK Hospital, Bagalkot, Karnataka, India
Received: 06 January, 2017; Accepted: 06 January, 2017; Published: 06 March, 2017
Divya Teja V, Doctor, 2nd DOMS, S. Nijalingappa Medical College and HSK Hospital, Room No: 46, PG Ladies hostel, Navanagar, Bagalkot-587102, Karnataka, India, Tel: 9441686800; E-mail:
Brijesh P, Anupama SC, Divya Teja V (2017) Evaluation of Retinal Nerve Fiber Layer Thickness using Spectral Domain-Optical Coherence Tomography in Glaucomatous, Ocular Hypertensive and Normal Eyes and its Correlation with Visual Fields. J Clin Res Ophthalmol 4(1): 010-013. 10.17352/2455-1414.000037
© 2017 Brijesh P, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Glaucoma; Ocular hypertension; Optical coherence tomography; Retinal nerve fiber layer; Perimetry
RNFL: Retinal Nerve Fiber Layer; OCT: Optical Coherence Tomography; ONH: Optic Nerve Head; SLP: Scanning Laser Polarimetry; HRT: Hiedelberg Retinal Tomography; CDR: Cup-Disc Ratio; BCVA: Best Corrected Visual Acuity; MD: Mean Defect
Objective:M The aim of the study was to correlate the findings of peripapillary retinal nerve fiber layer (RNFL) thickness calculated with optical coherence tomography(OCT) with visual field changes in glaucomatous, ocular hypertensive and normal eyes.
Materials and Methods: 30 normal, 30 ocular hypertensive and 30 glaucomatous eyes were included in the study. All underwent applanation tonometry, disc evaluation, octopus white on white (W/W) perimetry and OCT. Average and segmental RNFL thickness values were compared among all groups. A correlation was sought between global indices of perimetry and RNFL thickness in ocular hypertensive group.
Results: Of the 90 eyes (mean age: 51.20±9.23 years), the mean RNFL thickness was significantly less in ocular hypertensives 83.83±26.20μm; P< 0.001) and glaucomatous eyes (55.33±34.72 μm; P <0.001), than in normal (103.27±16.23 μm). Ocular hypertensives had thinner RNFL in the superior, inferior, nasal and temporal quadrants (P < 0.001) when compared to normal. The RNFL thickness could not be significantly correlated with global indices of visual fields in ocular hypertensives.
Conclusion: Optical coherence tomography is capable of detecting changes at the level of RNFL in ocular hypertensive eyes with normal appearance of discs and W/W perimetry fields.
IntroductionGlaucoma is a group of many conditions sharing a final common pathway characterized by accelerated death of retinal ganglion cells and their retinal nerve fiber layer (RNFL) axons resulting in characteristic visual field defects and corresponding optic nerve head anatomical changes. The ability to detect structural loss is fundamental in the diagnosis and management of glaucoma. While glaucomatous structural damage can be assessed subjectively by clinically examining the optic nerve head (ONH) and peripapillary retinal nerve fibre layer (RNFL), the introduction of ocular imaging modalities into clinical management has allowed for supplemental objective and quantitative evaluation of ocular structure.
Optical coherence tomography (OCT), first described in 1991, is a noncontact, noninvasive imaging technique that can reveal layers of the retina by looking at the interference patterns of reflected laser light. Automated software segmentation algorithms are able to outline the retinal nerve fiber layer with much precision, which is relevant in glaucoma since this layer is thinned as ganglion cells are lost. OCT became widely popular in 2002 with the release of Stratus OCT, a time-domain technology (TD-OCT) that was well-studied and validated for use in glaucoma and retina and went on to become a standard structural imaging test. Only four years later, spectral-domain OCT (SD-OCT), a fourier-domain OCT, which improved upon TD-OCT by capturing more data in less time at a higher axial image resolution, around 5 µm is developed. OCT thus produces high-resolution cross-section images of the posterior pole of the eye, and can be useful in glaucoma diagnosis for its ability to study the diffuse and localized thinning of RNFL . Some studies suggest that OCT may be superior to scanning laser polarimetry (SLP) and Heidelberg retinal tomography (HRT) for detecting a specific pattern of reduction in the average and focal RNFL thickness as well as the disc parameters [2,3]. Individuals with glaucoma are usually asymptomatic until late the disease processes and it is possible to either slow or prevent the progression of vision loss if detected early by adequate treatment. Therefore, a glaucoma screening tool for the general population is desirable.
White on White (W/W) perimetry is a generally accepted method for monitoring visual field damage in glaucoma patients and suspects. Glaucoma patients suffer a loss of about 40% of their retinal ganglion cells before this loss is picked up on W/W perimetry .
The aim of the study was to measure the RNFL thickness by OCT in eyes with glaucoma and in ocular hypertensives and to compare the results with that of age-matched normal eyes and to correlate the findings with global indices of visual fields in ocular hypertensives.
Materials and Methods
A total of 90 eyes (30 normal, 30 ocular hypertensive and 30 glaucomatous eyes) of individuals (age range 30 to 70 years) attending SNMC Eye OPD at Bagalkot, between October 2015 and October 2016 were enrolled in this cross-sectional observational study. The study was approved by the ethical committee of our Institute. Informed consent was taken from all study subjects. All subjects had open angles on gonioscopy with best corrected visual acuity (BCVA) of 20/40 or better with clear lens. Inclusion criteria were
a) Normal eyes: No history of ocular surgery or laser treatment, intraocular pressure (IOP) of 21mmHg or less, normal slit-lamp examination, cup disc (CD) ratio 0.2 to 0.4, symmetrical cupping and normal W/W perimetry.
b) Ocular hypertension: IOP greater than 21mmHg on a diurnal day curve before treatment on at least two separate occasions with normal visual fields and CD ratio of 0.2 to 0.4.
c) Glaucoma: IOP greater than 21mmHg and an abnormal W/W perimetry that fulfilled the minimum criteria for glaucomatous visual field defects, namely, a cluster of three or more non-edge points in a location typical for glaucoma, all of which were depressed on pattern deviation plot at P <5% level and one of which was depressed at P <1% level, ONH defects characteristic of glaucomatous excavation, notching, focal or diffuse atrophy of RNFL, vertical CD ratio more than 0.6 or disc asymmetry more than 0.2 between the two eyes.
Exclusion criteria for all subjects included a BCVA worse than 20/40, angle abnormalities on gonioscopy, any other intraocular eye diseases, diseases affecting visual fields (pituitary lesions, demyelinating diseases, diabetes mellitus, the acquired immunodeficiency syndrome) or secondary causes of IOP increase (pseudoexfoliation, corticosteroid use, iridocyclitis, trauma) and any pathological condition, including retinal, that could affect the visual fields.
A detailed medical and surgical history was elicited from the patients. Slit-lamp biomicroscopy, visual acuity testing with refraction, ONH examination, applanation tonometry, gonioscopy, octopus perimetry and OCT evaluation of RNFL was performed in all groups. W/W perimetry was performed with Octopus 300 with Dynamic G2 Strategy. A reliable test was defined as having fewer than 20% false-positive or false-negative scores and fewer than 33% fixation losses. Perimetry and OCT examinations were performed on the same day.
Optical coherence tomography was performed by using Optovue spectral Domain OCT. The results were analyzed with Version 4.0.1 software. A-scan data centered over the optic nerve in which a 3.4 mm diameter circle of RNFL data is extracted to create what is referred to as the TSNIT map (temporal, superior, nasal, inferior, temporal). It is displayed as a false colour scale with the thickness values referenced to a normative database. The numeric values for all parameters are shaded as white, green, yellow, or red, with the yellow and red representing, < 5% and < 1%, respectively compared to the normative database. The TSNIT map displays RNFL thickness values by quadrants and clock hours. Three circular scans were obtained from each test eye. All scans were performed by the same investigator. An internal fixation target was used in all scans, and the location of each scan on the retina was monitored on the built-in infrared-sensitive video camera.The best quality, properly aligned scan was chosen for analysis. Average RNFL thickness was calculated globally and separately for superior, inferior, temporal and nasal quadrants.
The parameters compared were average RNFL thickness of the entire circumference of the optic disc and quadrant thickness consisting of superior (46 to 135 degrees), nasal (136 to 225 degrees), inferior (226 to 315 degrees) and temporal (316 to 345 degrees) quadrant areas between the three groups. Statistical significance is derived with Unpaired ‘t’ test between the groups. Correlations between RNFL thickness and visual field parameters were assessed by correlation coefficients (Pearson’s r).Data were reported as mean ± standard deviation (SD). A P value of less than 0.05 was considered statistically significant.
Ninety eyes (30 normal, 30 ocular hypertensive and 30 glaucomatous) were enrolled. There was no difference between the groups with regard to gender, race and age. Mean age of the patients was 51.20±9.23years. The mean age of patients in the normal group is 53.16±7.2yrs, in ocular hypertensive group is 50.46 ±9.53yrs and glaucoma group is 52.76±11.23.The mean vertical CD ratio was 0.26, 0.36 and 0.74 in normal, ocular hypertensive and glaucomatous eyes respectively. The RNFL thickness was greatest in the superior and inferior quadrants and thinner in the nasal and temporal quadrants in the normal group. The RNFL profile demonstrated the “double hump” pattern.
Mean RNFL thickness was 55.33±34.72 μm in glaucomatous eyes, 83.83±26.20 μm in ocular hypertensives and 103.27±16.23 μm in normal (Figure 1).
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