Jyoti Shetty1, Mohan Kannam2, Rachel Joseph3, Fauqia4
The retinal ganglion cell layer is the first cell layer within the retina to be affected by early glaucoma. Approximately, 50% of Retinal Ganglion Cells (RGC) are located within the macula, it is well known that patients with glaucoma can suffer a 20% to 50% loss of retinal ganglion cells before a defect becomes evident in standard perimetry. Hence, macular imaging is suggested to be a valuable alternative scanning location method for glaucoma diagnosis and assessing neural damage in glaucoma.
The aim of the study is to assess the diagnostic ability of perimacular Ganglion Cell Inner Plexiform Layer (GCIPL) thickness in patients with glaucoma using HD-cirrus OCT and its correlation with Retinal Nerve Fibre Layer (RNFL) thickness and other ONH parameters in different optic disc sizes in a tertiary referral eye care centre in southern India.
MATERIALS AND METHODS
Optic nerve head (200 x 200) and macular imaging (512 x 128) with cirrus HD-OCT was performed on 100 eyes of 66 glaucoma patients and 85 eyes of 50 control patients. Macular GCIPL thickness was assessed and correlated with peripapillary RNFL thickness and ONH parameters like disc area, rim area and cup volume.
Mean GCIPL thickness was thinner in eyes with glaucoma in comparison to controls (70.64 ± 12.24 micrometers versus 79.58 ± 0.51 micrometers). Mean RNFL thickness in eyes with glaucoma was thinner compared with controls (76.44 ± 16.36 micrometers vs. 90.62 ± 27.57 micrometers). Mean GCIPL segment thickness in all glaucomatous discs showed significant correlation (P<0.05) with corresponding mean RNFL quadrant thickness. Significant correlation was found in large discs (P<0.05), but the level of significance decreased in medium discs (P value- 0.05<P<0.10). Mean RNFL thickness showed statistically significant correlation to rim area (P<0.001) in large and medium discs, whereas mean GCIPL thickness showed significant correlation with rim area in large discs only. Other factors like disc area and cup volume did not show any correlation with mean RNFL and GCIPL thickness.
RNFL thickness analysis still remains the main quantitative analysis for glaucoma. GCIPL thickness analysis can also be used as a surrogate parameter to assess RNFL thickness loss in cases where RNFL analysis can be fallacious as in large peripapillary atrophy, abnormal disc vasculature and tilted disc provided macular pathology has been ruled out. RNFL thickness correlation with GCIPL thickness was not influenced by disc size. Rim area had significant positive correlation to mean RNFL thickness. Other optic nerve head parameters like disc area and cup volume did not show any correlation.