Abstract
Purpose:
To evaluate the relationship between visual function and macular ganglion cell complex (GCC) thickness measured by Fourier–domain optical coherence tomography (OCT) and evaluate the diagnostic value of GCC measurement compared to retinal nerve fiber layer (RNFL) thickness and macular thickness in detecting early, moderate, and severe glaucomas.
Methods:
Subjects underwent standard automated perimetry (SAP), OCT imaging with optic nerve head mode and GCC mode. The relationship between OCT parameters (mean GCC thickness, mean RNFL thickness, and macular thickness) and perimetry global indices (mean deviation [MD] and pattern standard deviation [PSD]) was evaluated by regression analysis. Diagnostic values of mean RNFL thickness, GCC parameters, and macular thickness were compared with the area under the receiver operating characteristic curves (AUC).
Results:
A total of 84 eyes, 42 of each normal and primary open-angle glaucoma patients were included in the study. Compared with linear models, second-order polynomial models better described relationships between GCC thickness and MD (P < 0.001), and between GCC thickness and PSD (P = 0.00). RNFL parameter, inferior RNFL thickness had the highest AUC for detecting early glaucoma. The AUC of mean GCC thickness for early glaucoma was higher than that of mean RNFL; however, the difference was not significant (P = 0.09), which was higher than that of macular thickness.
Conclusion:
The relationship between visual field (VF) sensitivity and GCC thickness is best expressed by the curvilinear function. Macular GCC thickness and RNFL thickness showed similar diagnostic values but were better than macular thickness for detecting early glaucoma but inferior to macular thickness and RNFL thickness for detecting moderate glaucoma.
Keywords: GCC thickness, macular thickness, RNFL thickness
Glaucoma is a chronic, progressive optic neuropathy caused by a group of ocular conditions, which leads to damage of the optic nerve with loss of visual function. The most commonly known modifiable risk factor is raised intraocular pressure.[1]
With standard perimetric techniques, 25% to 35% of retinal ganglion cells (RGCs) may be lost in an eye with normal field by the time reproducible early field defects are found,[2] and 10% or fewer axons may remain by the stage of severe field lost.[3]
When correlating retinal ganglion cell atrophy with automated perimetry in patients with glaucoma, a 20% loss of cells, especially large ganglion cells in central 30 degrees of the retina, correlated with a 5-dB sensitivity loss, whereas 40% loss corresponded with 10-dB decrease, and some ganglion cells remained in areas with 0 dB sensitivity.[4]
Several clinical studies confirmed that a decline in RGCs precedes functional changes detected on SAP in glaucomatous eyes, confirming that a combination of structural and functional tests might offer an optimal assessment of neural damage and its progression.[5,6,7] Therefore, developing methods to quantify RGC-related glaucomatous changes could lead to glaucoma detection at an earlier stage and more accurate tracking of glaucoma progression.
Optical coherence tomography (OCT) allows for non-invasive imaging of glaucomatous structural damage involving the optic nerve, peripapillary retinal nerve fiber layer (RNFL), and macula. Of these, the quantification of circumpapillary RNFL represents the most commonly used OCT parameter because it has been considered a useful method in assessing structural loss of RGCs in glaucoma.[8,9] However, this method analyses only the axonal portion of RGCs without considering cell bodies and dendrites, which are also affected in glaucoma and reside in the ganglion cell layer (GCL) and inner plexiform layer (IPL), respectively.[10,11]
With the development of newer OCT, automatized segmentation of inner retinal layers has become possible. Macular ganglion cell complex (GCC) includes all three innermost retinal layers potentially involved in glaucomatous damage (RNFL, GCL, and IPL). In addition, segmentation of GCC thickness is traced from the inner limiting membrane and outer IPL boundary.[10,11,12]
However, to the best of our knowledge, there are no studies that have compared the diagnostic value of RNFL thickness, macular GCC thickness, and macular thickness simultaneously in one study.
In the present study, we, therefore, assessed relationships between VF sensitivity and GCC thickness by Fourier domain (FD)-OCT (RTVue-100, 3D OCT system 6.2 version) and evaluated the diagnostic value of GCC thickness in early, moderate, and severe glaucoma. These results were compared with mean RNFL thickness measured by system optic nerve head (ONH) mode and macular thickness measured using macular three-dimensional (3D) scan protocol.
Methods
Participants were enrolled from the Glaucoma–Cataract Clinic of a tertiary eye care hospital in Central India from June 2021 to December 2022. The study was approved by the institutional ethics committee and complied with the tenets of the Declaration of Helsinki. Patients provided written informed consent.
All subjects underwent applanation tonometry, gonioscopy, and fundus examination with a +90D lens, automated refractometry, standard VF testing, and FD-OCT (RTVue-100; Optovue) scanning after pupillary dilation. All examinations were performed in a single day.
Normal eyes were defined as those with no family history of glaucoma in a first-degree relative, no history of intraocular surgery, and no retinal pathological features. Also, they had the best-corrected visual acuity of 6/12 or better, with the refractive error between + 3.00 and − 6.00 D, intraocular pressure (IOP) of 21 mm Hg or lower, normal-appearing ONH, and reliable normal VFs.
Glaucomatous eyes were defined as those with glaucomatous VF defect confirmed by two reliable VF examinations and by the appearance of the glaucomatous optic disc with a typical loss of neuroretinal rim (cup-to-disc ratio >0.5; inter eye cup asymmetry >0.2; or neuroretinal rim notching, focal thinning, disc hemorrhage, vertical elongation of the optic cup, or RNFL wedge defect).
Glaucoma is categorized into three subgroups according to the modified Hodapp–Anderson–Parrish grading scale based on the MD of VFs.
Early glaucoma as VF loss with MD ≥ −6 dB,
Moderate glaucoma as MD between − 6 and − 12 dB,
Severe glaucoma as MD worse than − 12 dB.
Visual field examination
Standard visual field (VF) testing was performed using static automated perimetry (Optopol PTS 1000 Projection perimeter, with fast threshold, 30-2 test program). The VF was considered reliable when fixation losses were less than 20%, and false-positive and false-negative errors were less than 15%. Mean VF sensitivity was calculated using the perimetry software and expressed as MD, PSD. A field defect was defined as having three or more significant (P < 0.05) non–edge-contiguous points with at least one at the P < 0.01 level on the same side of the horizontal meridian in the pattern deviation plot and confirmed with at least two VF examinations.
OCT measurements
Mean GCC, RNFL, and macular thicknesses were measured using FD-OCT, which acquires 26,000 A-scans per second and provides a 5-µm depth resolution in tissue. RNFL thickness was determined using the ONH mode, in which data were along a 3.45-mm diameter circle around the optic disc. Mean, superior, and inferior RNFL thicknesses were calculated. GCC scan was centered 1 mm temporal to the fovea and covered a square grid (6 mm × 6 mm) on the central macula. GCC thickness was measured from the internal limiting membrane to the outer inner plexiform layer boundary, and mean, superior, and inferior GCC thicknesses were calculated. Two pattern-based diagnostic parameters were also obtained. Focal loss volume (FLV) was computed as the integral of deviation in the areas of significant focal GCC loss divided by map area. Global loss volume (GLV) was computed as the sum of negative fractional deviation in the entire area.[10] Macular thickness was measured using a macular three-dimensional (3D) scan protocol. A 3D scan consists of several horizontal line scans composing a 6 mm × 6 mm box. Images were excluded when the signal strength index was less than 35, overt misalignment of the surface detection algorithm occurred, or there was overt decentration of the measurement circle location.
Statistics
The age distribution was studied using an independent sample t-test. According to the central limit theorem, with a large enough sample size (usually around 30 or more) from the population, the distribution of sample means or sums approximates a normal distribution.
Mean GCC, RNFL, and macular thicknesses of normal eyes were compared with glaucomatous eyes by t-test. Analysis of variance (ANOVA) and the Scheffe post hoc multiple comparisons test were used to compare different glaucoma severity groups.
The relationships between mean RNFL/GCC thickness and MD/PSD were evaluated with linear and non-linear (second-order and third-order polynomial) regression analyses. Regression models were evaluated with the Akaike information criterion (AIC) and extra-sum-of-square F test.[13,14] The F test was used to test whether an alternative non-linear model (second-order polynomial or third-order polynomial) fits data better than the linear model.[14] The regression equation was plotted to display changes in visual sensitivity according to the extent of RNFL or GCC or macular damage.
Receiver operating characteristic (ROC) curves assessed the ability of macular thickness, RNFL, and GCC parameters to detect glaucomatous changes in patients with various levels of glaucoma severity. An area under the ROC curve (AUC) value of 1.0 represented perfect discrimination, whereas an AUC of 0.5 represented discrimination that is no better than results obtained by chance. Differences in diagnostic ability (AUC) of RNFL and GCC were tested for statistical significance by a previously described method.[15] All statistical analyses were performed using SPSS for Windows, version 12.0.0, SPSS Inc, Chicago, IL. P <0.05 was considered statistically significant.
Results
A total of 84 eyes of 42 patients were included in the study, 42 normal and 42 glaucomatous eyes. According to the Modified Hodapp Classification of 42 Glaucomatous eyes, 12 were early glaucomatous, 12 were moderate glaucomatous, and 18 were severe glaucomatous.
The mean age of patients in the normal group was 58.04 ± 8.67 years and that in the POAG group was 64.86 ± 9.71 years, with age distribution between the normal and POAG groups statistically significant (P = 0.05).
In the normal group, 22 (52.38%) eyes were of males and 20 (47.62%) were of females, and in the POAG group, 26 (61.90%) eyes were of males and 16 (38.10%) were of females. Forty-eight (57.14%) eyes were of males and 36 (42.86%) were of females, this gender distribution was statistically significant (P < 0.001) [Table 1].
Table 1.
Demographic characteristics
| Case (n=42 Eyes) | Control (n=42 Eyes) | P | |
|---|---|---|---|
| Age in years | 63.869.72 | 58.058.67 | 0.05 (Significant)* |
| Eyes of Male n (%) | 26 (61.90) | 22 (52.38) | 0.00 (Highly Significant)* |
| Eyes of Female n (%) | 16 (38.10) | 20 (47.62) | |
| Total | 42 | 42 |
*Obtained using independent sample t-test for age distribution and Chi-square test for sex distribution
Perimetry measurements
The mean VF MD (dB) in normal subjects and early, moderate, and severe glaucoma groups were −2.58 ± 2.66, −2.28 ± 2.04, −9.09 ± 1.54, and −18.47 ± 5.07 dB, respectively. The difference in MD between the normal group and POAG group (all comparisons, P < 0.001) and between various glaucoma severity groups (P < 0.001) was statistically significant.
The mean VF PSD (dB) in the normal group and POAG group and early, moderate, and severe glaucoma groups were 2.95 ± 1.43, 6.58 ± 2.58, 4.02 ± 1.69, 7.79 ± 2.18, 7.47 ± 2.14, respectively. Mean PSD between normal and POAG groups (P < 0.001) differed statistically significantly. The difference in the mean PSD in the moderate and severe glaucoma groups was statistically insignificant (P = 1.00); however, there was a statistically significant difference between the early and moderate groups (P < 0.001) and between the early and severe groups (P < 0.001).
Perimetry parameters (MD and PSD) and OCT parameters, RNFL and GCC, and macular thickness measurements of control and glaucoma groups are presented in Table 2.
Table 2.
Perimetry and OCT variables
| Variable | Mean±SD |
P* | Mean±SD |
P † | |||
|---|---|---|---|---|---|---|---|
| Perimetry | Glaucoma (n=42) | Normal (n=42) | Early Glaucoma (n=12) | Moderate Glaucoma (n=12) | Severe Glaucoma (n=18) | ||
| MD, dB | -11.17±7.76 | -2.58±2.66 | 0.00 | -2.28±2.04 | -9.09±1.54 | -18.47±5.07 | 0.00 |
| PSD, dB | 6.58±2.58 | 2.95±1.43 | 0.00 | 4.02±1.69 | 7.79±2.18 | 7.47±2.14 | 0.00 |
| VCDR | 0.78±0.19 | 0.52±0.14 | 0.00 | 0.75±0.18 | 0.69±0.21 | 0.87±0.17 | 0.04 |
| HCDR | 0.80±0.23 | 0.54±0.15 | 0.00 | 0.78±0.25 | 0.70±0.24 | 0.87±0.18 | 0.13 |
| OCT Disc area, mm2 | 2.61±0.50 | 2.46±0.58 | 0.19 (Not Significant) | 2.54±0.53 | 2.88±0.33 | 2.48±0.52 | 0.08 |
| RNFL µm | |||||||
| Mean | 84.27±14.23 | 105.23±4.52 | 0.00 | 92.44±9.34 | 89.87±7.91 | 75.09±15.26 | 0.00 |
| superior | 86.10±15.24 | 101.75±6.66 | 0.00 | 92.06±11.78 | 94.44±7.73 | 76.57±16.17 | 0.00 |
| Inferior | 82.43±14.88 | 108.70±7.88 | 0.00 | 92.90±10.06 | 85.31±9.30 | 73.54±15.68 | 0.00 |
| GCC µ m | |||||||
| Mean | 78.59±11.64 | 92.48±5.44 | 0.00 | 86.23±7.80 | 82.58±6.37 | 70.85±12.05 | 0.00 |
| Superior | 79.91±12.10 | 94.85±9.32 | 0.00 | 87.14±7.49 | 85.09±5.95 | 71.65±12.88 | 0.00 |
| Inferior GCC | 77.28±11.87 | 90.18±4.51 | 0.00 | 85.32±9.11 | 80.07±7.35 | 70.06±12.03 | 0.00 |
| FLV % | 7.38±5.43 | 1.54±1.42 | 0.00 | 2.07±1.89 | 7.88±5.07 | 10.58±4.61 | 0.00 |
| GLV % | 22.70±10.82 | 8.66±3.36 | 0.00 | 13.03±6.62 | 22.07±6.33 | 29.57±10.58 | 0.00 |
| Macular Thickness (MT), µm | |||||||
| MT | 239.21±22.10 | 253.74±18.72 | 0.00 | 235.33±21.28 | 242.00±11.11 | 239.94±28.08 | 0.76 |
*Differences between normal and glaucoma. †Differences among severity levels of glaucoma
OCT measurements
RNFL and GCC measurements were the highest in the control group and decreased as glaucoma severity increased [Table 2]. RNFL thickness (normal, 105.23 ± 4.52; early, 92.44 ± 9.34; moderate, 89.87 ± 7.91; severe, 75.09 ± 15.26). The mean GCC thickness followed a similar pattern (normal, 92.48 ± 5.44; early, 86.23 ± 7.80; moderate, 82.58 ± 6.37; severe, 70.85 ± 12.05). Differences in RNFL and GCC parameters between normal and glaucomatous eyes were significant (all comparisons, P < 0.001).
Mean RNFL thickness differed significantly between early and severe glaucoma (P = 0.00) and between moderate and severe glaucoma (P = 0.00). The difference in the mean RNFL thickness between early and moderate glaucoma was statistically insignificant (P = 1.00).
The difference in mean GCC thickness between normal and POAG eyes was significant (all comparisons, P < 0.001). The mean GCC thickness differed significantly between early and severe glaucoma (P < 0.001) and between moderate and severe glaucoma (P = 0.00). The difference in the mean GCC thickness between early and moderate glaucoma was statistically insignificant (P = 1.00).
Macular thickness (µm) differed significantly between the normal group (253.74 ± 18.72) and the POAG group (239.21 ± 22.10) (P = 0.002). However, the difference in macular thickness between various glaucoma severity groups (early, 235.33 ± 21.28; moderate, 242.00 ± 11.11; severe, 239.94 ± 28.08) was statistically insignificant (all comparisons P = 1.00).
Relationship between visual field sensitivity and GCC thickness
The relationship between perimetry global indices, MD, and PSD with OCT parameters was evaluated by regression analysis [Table 3].
Table 3.
Prediction of MD and PSD from OCT parameters by regression analysis
| Linear |
Second-order polynomial |
Third-order polynomial |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| R 2 | Adjusted R2 | R 2 | Adjusted R2 | F | P* | R 2 | Adjusted R2 | F | P † | |
| MD | ||||||||||
| RNFL Mean | 0.47 | 0.46 | 0.54 | 0.51 | 22.70 | 0.00 | 0.55 | 0.52 | 23.31 | 0.00 |
| GCC Mean | 0.51 | 0.59 | 0.52 | 0.50 | 21.31 | 0.00 | 0.52 | 0.5 | 21.46 | 0.00 |
| Macular thickness | 0.01 | -0.02 | 0.01 | -0.05 | 0.10 | 0.91 | 0.01 | -0.05 | 0.10 | 0.90 |
| PSD | ||||||||||
| RNFL Mean | 0.08 | 0.06 | 0.19 | 0.15 | 4.51 | 0.02 | 0.18 | 0.14 | 4.26 | 0.02 |
| GCC Mean | 0.12 | 0.10 | 0.26 | 0.23 | 6.98 | 0.00 | 0.25 | 0.26 | 6.62 | 0.00 |
| Macular thickness | 0.01 | -0.02 | 0.02 | -0.04 | 0.29 | 0.75 | 0.02 | -0.04 | 0.29 | 0.75 |
*Comparison of linear and second-order models. †Comparison of linear and third-order models
The structure–function relationship [Fig. 1] was better explained with non-linear models when visual sensitivity MD (dB) was plotted against RNFL thickness (linear versus second-order model, P < 0.001; linear versus third-order model, P < 0.001). Non-linear models also better explained the relationship between VF MD and GCC thickness (linear versus second-order model, P < 0.001; linear versus third-order model, P < 0.001). Similarly, non-linear models better described relationships between VF PSD and mean RNFL thickness (linear versus second-order model P = 0.02, linear versus third-order model P = 0.02), and between VF PSD and mean GCC thickness (linear versus second-order model P = 0.00, linear versus third-order model P = 0.00). Macular thickness did not show any statistically significant relationship with MD (dB) and PSD (dB).
Figure 1.
Second-order regression models of the relationships between VF MD and mean RNFL thickness (a), between VF MD and mean GCC thickness (b), between VF MD and macular thickness (c), VF PSD and mean RNFL thickness (d), between VF PSD and mean GCC thickness (e), between VF PSD and macular thickness (f), measured by OCT
Diagnostic value of GCC and RNFL and macular thicknesses among different glaucoma severity groups
The diagnostic values of mean RNFL thickness, GCC parameters (mean thickness, FLV, and GLV) and macular thickness were compared with ROC curves [Table 4].
Table 4.
Evaluation of OCT parameters as diagnostic tests with the area under the ROC curve
| Normal versus early glaucoma | Normal versus moderate glaucoma | Normal versus severe glaucoma | |
|---|---|---|---|
| Mean (RNFL) | 0.73 (74.45-105.32) | 0.65 (69.31-100.28) | 0.18 (55.39-105.34) |
| Mean (GCC) | 0.76 (75.51-99.520 | 0.64 (66.56-90.98) | 0.16 (52.93-94.58) |
| FLV | 0.08 (0.25-6.16) | 0.57 (1.11-5.35) | 0.79 (2.64-20.67) |
| GLV | 0.12 (1.20-22.81) | 0.49 (11.08-33.12) | 0.82 (9.11-45.73) |
| Macular thickness | 0.39 (212.00-273.00) | 0.68 (227.00-261.00) | 0.44 (212.00-319.00) |
| Superior (RNFL) | 0.63 (72.55-110.15) | 0.73 (75.91-106.32) | 0.20 (75.91-106.32) |
| Inferior (RNFL) | 0.79 (76.36-110.15) | 0.60 (62.71-99.22) | 0.18 (62.71-99.22) |
| Superior (GCC) | 0.74 (73.67-97.93) | 0.67 (73.67-97.93) | 0.16 (73.33-96.32) |
| Inferior (GCC) | 0.76 (69.92-101.55) | 0.62 (69.92-101.55) | 0.19 (59.77-86.23) |
Fig. 2 shows AUCs for mean RNFL thickness, mean GCC thickness, FLV of GCC, and GLV of GCC and macular thickness according to visual field sensitivity: normal versus early glaucoma, normal versus moderate glaucoma and normal versus severe glaucoma, respectively.
Figure 2.
AUCs for mean RNFL thickness, mean GCC thickness, FLV of GCC, and GLV of GCC and macular thickness according to visual field sensitivity: normal versus early glaucoma (a), normal versus moderate glaucoma (b), and normal versus severe glaucoma (c)
For early glaucoma
The diagnostic value of mean GCC (AUC = 0.76) was greater than that of mean RNFL thickness; however, the difference was not significant (P value = 0.09). However, the diagnostic value of mean GCC thickness (AUC = 0.76) and that of mean RNFL (AUC = 0.73) was greater than that of macular thickness (AUC = 0.39) (P value = 0.00). Inferior RNFL (AUC = 0.79) was best able to diagnose early glaucoma.
For moderate glaucoma
The diagnostic value of macular thickness (AUC = 0.68) was greater than that of mean RNFL thickness (AUC = 0.65), which was better than that of mean GCC (AUC = 0.64) (P value = 0.00). Superior RNFL thickness (AUC = 0.73) was best able to diagnose moderate glaucoma.
For severe glaucoma
GLV was best able to diagnose severe glaucoma (AUC = 0.82). When compared to the mean GCC thickness (AUC = 0.16) and mean RNFL thickness (AUC = 0.18), macular thickness (AUC = 0.44) had greater diagnostic value; however, this discrimination in the diagnostic value between macular thickness, mean GCC thickness, and mean RNFL thickness was by chance.
Discussion
In this study, we found that peripapillary RNFL thickness and macular GCC thickness had similar structure–function relationships with VF sensitivity and similar diagnostic values for glaucoma detection but were better than macular thickness. Mean GCC thickness appeared to be a better predictor of early glaucoma than mean RNFL thickness; however, the difference was not significant.
In previous cross-sectional studies, regression analysis has been effectively used for structure–function relationships during disease progression.[14] The relationship between dB light sensitivity and the number of ganglion cells appears to be curvilinear[16,17] Results of this study for RNFL and GCC thickness conformed to previous studies that have demonstrated that second- and third-order regression models best describe the relationship between VF sensitivity and RNFL thickness[14,18,19] and GCC thickness.[20]
In this study, curvilinear regression models of the relationship between RNFL and VF sensitivity were consistent with the results from most previous investigations. Similarly, second- and third-order regression models of GCC thickness versus VF sensitivity yielded stronger structure–function associations compared with the first-order regression model. The correlation between VF sensitivity measured on a logarithmic scale (in decibels) with structural parameters measured on a linear scale accentuates changes at low decibel levels while minimizing the changes at high decibel levels, accounting at least in part for the curvilinear relationship.[16] In this study, there was no statistically significant relationship between VF sensitivity and macular thickness. However, some studies suggest that macular thickness correlate with VF parameters and RNFL parameters in glaucoma patients.[21] Some studies suggest that glaucomatous damage to the macula early in the disease can be missed and/or underestimated with standard VF tests that use a 6-degree grid, such as the 24-2 VF test.[22] In our study, VF sensitivity and macular thickness did not show a statistically significant relationship, which could be because of the small sample size or because glaucomatous damage to the macula early in the disease may have been missed and/or underestimated.
Studies have demonstrated that RNFL measurements are significantly more accurate than macular thickness in glaucoma detection.[23,24,25]
The RTVue directly measures the thickness of the inner three retinal layers. By targeting cells directly affected by glaucoma in the area of their highest concentration, it is believed to detect glaucoma earlier. In a few studies, the diagnostic value of RNFL and GCC measurements is compared with that of FD-OCT and results have shown that diagnosis using macular GCC parameters is comparable with diagnosis using circumpapillary RNFL measurements.[10,26] In this study, we observed similar AUC results for glaucoma detection between peripapillary RNFL and macular GCC thickness, irrespective of disease severity.
Mean GCC thickness appeared to be a better diagnostic marker for early glaucoma compared with RNFL thickness, although the AUC difference was not significant. This finding may be explained, in part, by the fact that GCC is a more direct measure of RGC integrity. Macular GCC parameters have a theoretical advantage over peripapillary RNFL parameters in diagnosis because RGC loss occurs early in the pathogenesis of glaucoma. Further, early RGC loss typically gives rise to isolated damage in the paracentral areas (10°–20°). Macular GCC scan is centered on the fovea, covers a 6 × 6-mm grid on the central macula, and readily detects early GCC loss.[20]
In our study, macular thickness OCT scan was able to diagnose moderate and severe glaucoma better than RNFL and GCC thickness. This can be explained by the fact the RNFL thickness measurements at the advanced stage of glaucoma represent mainly glial cells, the “floor effect” and hence OCT of the macula is often helpful in assessing progression in advanced glaucoma.[27] the same fact explains results in severe glaucoma that the discrimination in diagnostic value between macular thickness, mean GCC thickness, and mean RNFL thickness was not better than by chance.
GLV and FLV are pattern diagnostic parameters that reflect different aspects of GCC loss, representing the volume of GCC loss in the macula with differing levels of focality.[10] GLV had the highest diagnostic value than mean GCC thickness for severe glaucoma.
Limitations of the study were that it had a relatively small sample size and was a cross-sectional study. Also, the full spectrum of glaucoma patients was lacking and the reproducibility of parameters was lacking. Further, large sample size prospective studies are needed to endorse the findings of this study and know the value of macular GCC thickness in monitoring the progression of the disease.
Conclusion
The relationship between visual function and macular ganglion cell complex thickness measured by Fourier- domain optical coherence tomography was curvilinear.
Also, the diagnostic value of macular GCC thickness was comparable to RNFL thickness and was better than macular thickness for the detection of early glaucoma but was inferior to macular thickness and RNFL thickness for the detection of moderate glaucoma. Macular thickness can be used for the detection of moderate glaucoma. Hence, GCC and RNFL parameters may be considered complementary and better diagnostic tools than macular thickness in early diagnosis of primary open-angle glaucoma.
Financial support and sponsorship:
Nil.
Conflicts of interest:
There are no conflicts of interest.
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