Central corneal thickness and its relationship with IOP, visual fields and optic disc parameters among glaucoma patients attending the Eye Hospital at University Teaching Hospitals in Lusaka, Zambia

Abstract

Background: Glaucoma is a heterogeneous group of optic neuropathies characterized by an acquired loss of retinal ganglion cells, optic nerve atrophy and Visual Field Defects (VFD). Raised Intraocular Pressure (IOP) is the only causal risk factor for glaucoma that can be therapeutically and surgically manipulated to change the course of the disease process. Though Goldman Applanation Tonometry (GAT) is the “gold standard” for IOP measurement, readings of IOP with GAT are believed to be influenced by Central Corneal Thickness (CCT). The study evaluated the correlation of CCT and IOP with VFD parameters like Mean Deviation (MD),
Pattern Standard Deviation (PSD) and Cup-to-Disc Ratio (CDR) in Primary Open Angle Glaucoma (POAG) patients.
Objective: To determine the relationship of central corneal thickness, intraocular pressure, visual fields and optic disc parameters in Zambian primary open angle glaucoma patients.
Methods: A cross-sectional study was conducted in 2014 from January to September and all glaucoma patients visiting the University Teaching Hospitals – Eye Hospital during the study period were included if they consented to it and met the inclusion criteria. A total of 166 randomly selected newly diagnosed glaucoma patients aged 18 years and above were recruited. The CCT was measured using Kacon Ophthalmic Ultrasound system and IOP was measured by GAT. Analyses were carried out considering the level of
significance at 5%.

Results: One hundred and sixty-six newly diagnosed glaucoma patients aged 18 to 88 years were included into the study. There were 85 (51.2%) males and 81 (48.8%) females with a mean age being 51.31 years. The mean IOP was 23.60 (±10.40) mmHg. The mean CCT was 531.9 (±40.59). All the participants had primary open angle glaucoma POAG. Thin CCT was significantly correlated with vertical CDR (r= - 0.023, and 0.011). Thin CCT was also significantly associated with worsened MD of visual field (r= - 0.033 and p=0.023) and PSD (r= - 0.027 and p=0.012).
Conclusions: The mean CCT of Zambian POAG patients is thinner as compared to other races. CCT was positively correlated with IOP. Patients who had thicker CCT were more likely to have low IOP compared to patients who had thinner CCT. In the POAG patients thinner CCT was associated with greater cup disc ratio and Visual Field (VF) damages than those with a thicker CCT