|Year : 2022 | Volume
| Issue : 2 | Page : 104-109
Comparative evaluation of the thickness of macula, ganglion cell layer, and retinal nerve fiber layer in emmetropes, myopes and myopes with lattice degeneration by using Cirrus high-definition optical coherence topography
Mamta Singh1, Bibhuti Prassan Sinha2, Pradeep Karak3
1 Department of Ophthalmology, PMCH, Patna, Bihar, India
2 RIO, IGIMS, Patna, Bihar, India
3 NMCH, Patna, Bihar, India
|Date of Submission||10-Jun-2021|
|Date of Decision||12-Jun-2021|
|Date of Acceptance||28-Jun-2021|
|Date of Web Publication||30-Aug-2022|
Dr. Mamta Singh
PMCH, Ashok Rajpath, Patna - 800 004, Bihar
Source of Support: None, Conflict of Interest: None
Purpose: To know the quantitative thickness changes occurring in the macula, retinal nerve fiber layer (RNFL), and ganglion cell layer (GCL) of the retina in myopic eyes (ME) and in ME with lattice degeneration (ME-LD) in comparison to emmetropic eyes, with the help of Cirrus HD Optical coherence topography (OCT) 5000 (Carl Zeiss Meditec Inc.). Methods: Hospital-based, nonrandomized prospective study involving 90 eyes, divided into three groups – Group A comprising 30 eyes with − 3–−6D of myopia, Group B comprising 30 eyes with − 3–−6D of myopia with LD and Group C with 30 emmetropic eyes. The central macular thickness (CMT), RNFL, and GCL analysis was done with Cirrus HD OCT 5000 (Carl Zeiss Meditec). Results: The CMT was significantly higher in Group A and B than Group C. There was no significant difference in CMT between Group A and B. Any of the group did not reveal significant difference in parafoveal thickness in any quadrant. Average RNFL, average GCL + inner plexiform layer (IPL), minimum GCL + IPL was significantly thicker in Group C than Group A and B. There was no significant difference between in CMT, average RNFL thickness, average GCL + IPL between Group A and B. Conclusion: There is a significant change in thickness of macula, RNFL, and GCL between emmetropes as compared to myopes and ME-LD but not between myopes and ME-LD. This underscores the need of incorporating a myopic normative database in the present normative built-up of Cirrus OCT. Patients of ME-LD, when being evaluated on different OCT-based parameters, can be considered the same as the myopic population.
Keywords: Cirrus high-definition optical coherence topography, central macular thickness, ganglion cell layer, myopic lattice degeneration, retinal nerve fiber layer
|How to cite this article:|
Singh M, Sinha BP, Karak P. Comparative evaluation of the thickness of macula, ganglion cell layer, and retinal nerve fiber layer in emmetropes, myopes and myopes with lattice degeneration by using Cirrus high-definition optical coherence topography. Kerala J Ophthalmol 2022;34:104-9
|How to cite this URL:|
Singh M, Sinha BP, Karak P. Comparative evaluation of the thickness of macula, ganglion cell layer, and retinal nerve fiber layer in emmetropes, myopes and myopes with lattice degeneration by using Cirrus high-definition optical coherence topography. Kerala J Ophthalmol [serial online] 2022 [cited 2022 Dec 8];34:104-9. Available from: http://www.kjophthal.com/text.asp?2022/34/2/104/355043
| Introduction|| |
Myopia has become an important public health scare affecting nearly 13.1% of school-going children in India and as high as about 84% in high school students in Taiwan. It is an independent risk factor for multiple ocular pathologies like amblyopia, open-angle glaucoma, ocular hypertension, posterior subcapsular cataract, retinal detachment, different myopic tractional maculopathy. With the advent of Optical coherence topography (OCT), it has become possible to do a quantitative real-time assessment of different layers of the retina. The study of macular thickness (MT), ganglion cell layer (GCL), and retinal nerve fiber layer (RNFL) thickness analysis has become an important tool in the assessment of the risk factors, early diagnosis, and treatment of ocular disorders. The qualitative and quantitative change in different components of the retinal layer in cases of myopia has been a subject of different studies but to the best of our knowledge, these changes have not been studied in myopic eyes with lattice degeneration (ME-LD). In this study, we assessed MT, GCL, and RNFL in ME and LD in comparison to emmetropic eyes with the help of Cirrus HD OCT 5000 (Carl Zeiss Meditec Inc., Dublin, CA).
| Methods|| |
It was a hospital-based, nonrandomized, prospective observational study conducted in accordance with the principles of the Declaration of Helsinki after getting approval from the institutional review board.
The study group included the equal number of individuals between 20 and 40 years of age with emmetropia, myopia, and ME-LD with refractive error of − 3–−6 D. Individuals with any other ocular or systemic pathology, prior history of ocular surgery or long term ocular medication affecting optic nerve head or RNFL thickness were excluded from the study. Individuals with media opacity affecting OCT analysis were also excluded.
Ninety eyes of 101 individuals between 20 and 40 years of age were included in the study. Patients <20 years were excluded as the normative database is not available in Cirrus HD OCT for individuals <18 years of age. The study population was divided into three groups – Group A with 30 eyes having the mean myopic spherical equivalent of −4.01 ± 1.79 Diopter, Group B with 30 ME-LD having the mean spherical equivalent of −4.6 ± 1.82 diopter, and Group C having 30 emmetropic eyes with spherical equivalent ±0.5D. The best-corrected visual acuity was 6/6 in all three groups on Snellen's visual acuity chart. All patients underwent comprehensive eye evaluation including cycloplegic refraction, slit-lamp examination, intraocular pressure measurement with applanation tonometry, pachymetry evaluation with Cirrus OCT, gonioscopy, and dilated fundus evaluation with indirect ophthalmoscopy.
OCT scan was performed under mydriasis with Cirrus high-definition (HD) OCT5000 (Carl Zeiss Meditec Inc., Dublin, CA, USA) which has an axial resolution of 5 microns and a scan speed of 27,000 A-scans per second. All the scans had signal strength of 6 or more, well centered over disc or macula and were done by single experienced operator. MT was assessed in a macular cube (512 × 128) consisting of 9 sectors of the early treatment diabetic retinopathy study grid from the internal limited membrane to retinal pigment epithelium. For the ease of calculation, only central subfield and the 4 surrounding Parafoveal inner sectors; inferior, superior, nasal, and temporal (I-S-N-T) were considered while evaluating the results. The outer 4 sectors were not considered in the evaluation. GCL analysis was done in macular cube protocol and is shown as average and minimum GCL + inner plexiform layer (IPL) thickness. In addition, the I-S-N (average of supero + infero-nasal)-T (average of supero + infero-temporal) GCL + IPL thickness were also considered in the calculation. RNFL thickness was assessed in 6 mm × 6 mm optic disc area (200 × 200) and average and thickness in I-S-N-T quadrants were evaluated.
Statistical analysis was done using unpaired two-tailed t-test and P < 0.05 was considered significant.
| Results|| |
The three study groups were age matched. The mean age of Group A (myopia) was 30.8 ± 6.24 years, of Group B (ME-LD) was 25.5 ± 4.68 years and of Group C (emmetropia) was 28.9 ± 7.23 years. The mean myopic spherical equivalent of Group A, B and C was − 4.01 ± 1.79D, −4.6 ± 1.82D, and ± 0.5D, respectively [Table 1].
|Table 1: Comparison of the thickness of macula, ganglion cell layer, and retinal nerve fiber layer in emmetropes, myopes and myopes with lattice degeneration|
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The average RNFL thickness of Group A (Myopia), B (ME-LD), and C (Emmetropia) was 84.73 μ ±8.68 μ, 86.30u ± 8.72 μ and 93.26 ± 8.61 μ respectively. The average RNFL thickness was higher in Group C as compared to Group A and B. The statistical difference between average RNFL thickness of Group A and B was not significant (P = −0.488) but there was a significant difference in thickness of average RNFL between Group C than those with Group A (P = <0.001) and B (P = 0.002) [Figure 1].
The quadrant-wise comparison of RNFL thickness in I-S-N-T quadrants was performed among three groups. The statistical analysis showed a significant difference between Group C, than Group A and B in superior (P = −0.028, 0.048 respectively) and inferior quadrant (P = −0.007, 0.033, respectively) but not in nasal and temporal quadrant. There was no significant difference between Group A and B in any of the quadrants.
The MT of central subfield of Group C was lesser (227.10 ± 13.08u) than Group A (249.30 ± 20.24u) and Group B (243.60 ± 28.12). The statistical difference was highly significant between Group C in comparison to Group A (P < 0.001) and B (P = 0.005) but not between Group A and B (P = 0.371) [Figure 2].
None of the inner Parafoveal segments of any group has any significant difference from each other in any of the quadrants.
The average and minimum GCL + IPL thickness was higher in Group C (82.3 ± 4.66 μ and 78.1 ± 9.44 μ) than Group A (77.2 ± 5.17 μ and 72.9 ± 8.07 μ) and B (77.4 ± 6.17 μ and 66.4 ± 17.3 μ). The difference in average and minimum GCL + IPL thickness was significantly higher in Group C than Group A (P < 0.001 and 0.025, respectively) and B (P = ‒0.001 and 0.002, respectively). There was no significant difference between Group A and B (P = ‒0.910 and 0.072, respectively) [Figure 3].
|Figure 3: Average ganglion cell layer + ganglion cell layer thickness in three groups|
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On comparison of GCL + IPL thickness in different quadrants, it was significantly different in every quadrant between Group A and C. On comparison of Group C and Group B, it was significantly different in all except temporal quadrant (P = ‒0.420). It was not significant in any quadrant between Group A and B.
| Discussion|| |
Myopia is one among the most common ocular pathology worldwide and LD is an important vitreoretinal fundus change seen in ME. The prevalence of LD in the general population is about 7%–11%. The primary basic pathogenesis behind LD has not been completely understood. The proposed theories are the regional developmental absence of the internal limiting membrane with defects in the fibers of the Müller's cells and abnormal vitreoretinal traction dynamics. Histological characteristic of LD are retinal thinning, vitreous liquefaction, vitreous adhesion at lattice margins, vascular changes, retinal pigment abnormalities, and accumulations of dense amorphous material. All these changes become more progressive toward the center of lesion.
RNFL thinning in myopes has been related to elongation and thinning of retina and sclera, which would spread the nerve fibers over a large surface area. In ME it has been reported that there is a temporal convergence of superotemporal and inferotemporal RNFL bundles with increasing myopia, leading to abnormal RNFL measurement.
Although Hoh et al. reported no correlation between RNFL thickness and refractive status of an individual, the average RNFL thickness in our study was significantly higher in emmetropic eyes (93.26 ± 8.61 μ) than myopes (84.73u ± 8.68 μ P < 0.001)) and in ME-LD (86.30 μ ± 8.72 μ P = ‒0.002). ME had slightly higher average RNFL thickness than ME-LD eyes, but the difference was not significant. This difference in results from that published by Hoh et al. can be due to different OCT machines used in these two studies (OCT 1, version 4.1 versus Cirrus HD OCT). Tai et al. in their Zeiss Cirrus HD-OCT-based study compared the RNFL thickness in 180 emmetropic eyes and 223 ME with different grades of myopic refractive error and reported thinner RNFL in all groups of myopia than in emmetropes. In a spectral-domain OCT-based study by Oner et al., the average RNFL thickness was again higher in emmetropes than myopes. Similar report has been published by Zha et al. in their study on 271 Chinese participants comparing the RNFL thickness with Spectralis OCT, among emmetropes and different grades of myopes. They demonstrated that ME had a thinner average global RNFL thickness compared with emmetropic eyes, while the high myopic eye had the thinnest average global RNFL thickness. A contradictory result of thicker RNFL in myopes than age-matched healthy individuals has been reported by Bozkurt et al. in their study based on GDx. This study included 41 degenerative ME of 25 patients with spherical refractive errors between −7.50 and −22.00D (mean − 12.5 ± 3.5D). This discrepancy was attributed to the high scleral rigidity as a result of peripapillary chorioretinal atrophy associated with high myopia, leading to an apparent increase in retardation values.
In our study, the evaluation of RNFL thickness in I-S-N-T segments showed significant difference between emmetropes and myopes/ME-LD only in superior and inferior quadrants but not in nasal or temporal quadrants. A similar report has been published by Rauscher et al. in their study of myopic individuals between 23 and 54 years of age with mean spherical equivalent of ‒5.40 D. The nasal and temporal RNFL thickness in their study showed no significant association with myopia. Another study based on Cirrus OCT by Kang et al., in a Korean study population of 269 subjects between 19 and 26 years of age, with mean spherical equivalent of ‒2.5 ± 2.29 D, reported that with increase in myopia and axial length, there is decrease in superior and inferior peripapillary RNFL thickness and increase in temporal RNFL thickness. In myopic subjects, the measured RNFL thickness may be less than the actual thickness, and owing to the temporal shift in the contour of the RNFL thickness profile, the superior and inferior RNFL may be deemed abnormal in comparison with the normative reference provided by Cirrus OCT. He suggested to avoid such misdiagnosis, a new normative RNFL profile for myopic patients is needed. Oner et al. based on RTvue standard deviation OCT comparing myopic and emmetropic individuals reported that average RNFL thickness and the RNFL thicknesses of the superotemporal, superonasal, inferotemporal, and lower temporal sectors were significantly different between the myopic and emmetropic eyes.
In their Cirrus OCT-based study, Tai et al. also has also published myopic group having thinner average RNFL than the emmetropic group and their RNFL was thinner in all quadrants except temporally. An Indian study on 118 ME of patients between 20 and 30 years of age by Kamath et al., has reported a significant decrease in average RNFL thickness in all quadrants except the temporal quadrant. They speculated that the insignificant change in the temporal quadrant might be due to the dragging of the retina toward temporal horizon and compression of bundles originating from the opposite hemisphere at the horizontal raphe, causing thinning of RNFL thickness in all quadrants except temporal. The decrease in RNFL thickness was lesser in nasal quadrants than in other quadrants.
Various conflicting results have been published on the association between refractive error and central MT. The study by Ooto et al. and Manassakorn et al. have reported no association between MT and myopia or other refractive error. Huynhet al have published thicker central MT in hyperopes in their study on the younger population of 6-year-old children. But this study was done on the Caucasian race and on an age group which is still is in the age of emmetropization. The MT in our study was lesser in emmetropes than in myopes or in ME-LD. There was a significant difference between emmetropes and in these two groups but not between myopes and ME-LD.
Similar result has been published by Lim et al. based on their study on 130 Asian myopic (‒0.25–‒14.25D) individuals between 19 and 24 years. They reported myopics having thinner parafovea and thicker fovea. Yau et al. in their study of the Chinese population of 168 eyes between 4 and 18 years of age reported that the central MT was significantly higher in myopics than the emmetropic group. The study by Wakitani et al. showed higher central MT in ME where it serves as compensatory mechanism at the expense of a thinner peripheral retina in order to preserve the fovea, which is more essential to vision.
None of the inner segments of any group has any significant difference from each other in any of the quadrant which is similar to result published by Samuel et al. who reported a significantly thicker fovea with decrease in spherical equivalent but no significant change in parafoveal MT with decrease in spherical equivalent. They have mentioned that increase in the axial length of myopia causes mechanical stretching of the sclera in the posterior pole. This causes traction of vitreous on the fovea in the ME. Thus the increase in the foveal thickening with increasing degree of myopia can be an early sign of vitreoretinal traction.
Since ganglion cell loss precedes RNFL loss in disorders like glaucoma, it may be useful to do ganglion cell analysis for early detection of disease. The average and minimal GCL + IPL thickness in our study was significantly different between myopes and emmetropes. On comparing GCL + IPL thickness in I-S-N-T segments in these two groups, the difference was again significant in all the quadrants. In one of the Cirrus OCT-based study conducted by Seo et al. on a population of similar age group (20–32 years) and refractive error (Mean spherical equivalent-3.58 ± 2.74 diopters), there was a decrease in GCL + IPL thickness noted with increasing myopia in all the sectors.
Study by Szumiński and Bakunowicz-Łazarczyk has also reported significantly lower GCL thickness in the superior and inferior quadrant in the population of high myopes of >6D of refractive error, in comparison to emmetropes. Zhao et al. has also stated significant relationship between refractive error and GCL thickness and the importance of considering the refractive status of person before going for GCL analysis.
In our study when we compared quadrantic GCL + IPL thickness between emmetropes and ME-LD, it was significantly higher in emmetropes in all quadrants except the temporal. The difference in GCL + IPL thickness between myopics and ME-LD was not significant.
We could not find studies based on the assessment of the thickness of macula, RNFL and GCL in ME-LD. However, the present study has got certain limitations like relatively small study population. Another potential source of error in measurement is using the same size scan circle (i.e., 1.7 mm) in different grades of myopia. At present, the normative database of Cirrus HD OCT is based on the mean refractive error of ‒0.82(±1.96) D. One needs to add a correction factor depending on the axial length of the myopic eye as reported by Kang et al. We tried to negate this error by choosing patients between −3 and −6D of myopia in both the myopic groups so that the difference in axial length does not play a large role here.
| Conclusion|| |
There was a significant change in studied OCT parameters between emmetropes when compared with myopes/ME-LD. However, myopes and ME-LD showed no significant difference. This underscores the need of incorporating a myopic normative database in the present normative built-up of Cirrus OCT.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]