Abstract
Purpose:
Imaging studies in glaucoma patients show that chronically elevated intraocular pressure (IOP) leads to a thinning of both the retinal nerve fiber layer around the optic nerve (RNFL) and the macular ganglion cell complex (mGCC) thickness (nerve fiber layer + retinal ganglion cell + inner plexiform layer). This study examined the relationship between the mGCC thickness and the RNFL thickness in non-human primates (NHPs) with chronic ocular hypertension (OHT) using a semi-automatic software for quantifying mGCC and RNFL thickness. Specifically the diagnostic sensitivity and repeatability of mGCC thickness vs. RNFL thickness was evaluated.
Methods:
Twelve Cynomolgus monkeys weighing 5.3±1.6kg and with approximately 15±4.2 years of age were used in this study. Animals had unilateral chronic OHT that was induced by circumferential laser treatment to the trabecular meshwork in one eye (OD) for approximately 9.5±2.3 years. RNFL thickness and mGCC thickness were measured bilaterally using optical coherence tomography (Bioptigen Inc., Durham, 27560). A semi-automated algorithm was utilized by three randomized and masked delineators to delineate the retinal layers. Both delineation and data acquisition were performed twice for repeatability measures. Statistical analysis were performed to compare the significance of mGCC thickness vs. that of RNFL thickness. OS (naïve eye) was used as a control for each subject and statistical significance was analyzed in OD (OHT eye) vs. OS for both mGCC and RNFL.
Results:
Both Cohen’s d value and the effective size coefficient indicate a larger degree of separation in mGCC vs. RNFL. mGCC showed Cohen’s d value and effective size coefficient of 2.13 and 0.73 respectively where RNFL had 1.31 and 0.54 for Cohen’s d and effective size. A larger chi-square value -17.38 vs. 8.24- for GCC vs. RNFL respectively, also revealed a larger difference in the log likelihood between mGCC thickness when compared with that of RNFL. Correlation coefficient of 0.76 suggest an acceptable repeatability b/w the two mGCC measurements.
Conclusions:
This study suggests that mGCC is more affected when compared to RNFL in NHPs with chronic OHT eyes. Additionally mGCC thickness measurements exhibit high potentials to be a good alternative or a complementary measurement to RNFL thickness assessment in the clinical evaluation of glaucoma.
Keywords: 531 ganglion cells •
688 retina