Large discs with large cups : a diagnostic challenge in Black African patients

Abstract

BACKGROUND : The study was undertaken in order to determine in patients with large optic discs and large optic cups, the proportion with physiologic cupping (normal eyes) misdiagnosed as glaucomatous; and further, to evaluate the possible relationship between optic disc size and central corneal thickness. METHOD AND DESIGN : A case series of 69 Black African patients with large discs (vertical disc height measuring >1.8 mm) and large cups (vertical cup to disc ratio ≥0.6) was evaluated to determine what proportion had glaucoma. Patients categorised as normal were further evaluated to determine what proportion were previously misdiagnosed and treated for glaucoma. Patients with a suspected diagnosis of glaucoma, normal tension glaucoma or primary open angle glaucoma were recruited from the glaucoma clinic at St John’s Eye Hospital, Soweto, South Africa. Outcome measures included corrected vertical disc height (VDH), vertical cup to disc ratio (CDR), intraocular pressure (IOP), central corneal thickness (CCT), retinal nerve fibre layer (RNFL) analysis and visual fields. RESULTS : Sixty-nine Black African patients (138 eyes) with large discs and large cups were evaluated. Forty-one patients (59%) were females and 28 (41%) were males. The mean age was 56 years. Of the 69 patients, 51 (74%) had physiologic cupping (normal eyes) and 18 (26%) patients were glaucomatous. Of the group of 51 patients with physiologic cupping, there were nine patients who were previously misdiagnosed with glaucoma and who had received treatment. VDH ranged between 1.9 and 3.2 mm (mean±SD, 2.3±0.26 mm). The distribution analysis of VDH measurements noted the largest cluster around 2.3 mm. CCT ranged between 454 μm and 618 μm (mean±SD, 516±37μm). Of the 138 eyes, 107 (77.5%) had CCT<544 μm. CONCLUSION : Large CDR in relation to large disc size may be normal physiological cupping. It can be misdiagnosed as glaucomatous if objective RNFL analysis is not carried out. In this study, nine (18%) patients from a group of 51 patients with physiologic cupping were misdiagnosed as glaucomatous. There was no linear correlation between CCT and VDH in this study (Pearson’s correlation coefficient was 0.13). The majority of eyes (77.5%) had thin corneas (CCT<544 μm).