Assessment of cup-to-disc ratio with slit-lamp funduscopy, Heidelberg Retina Tomography II, and stereoscopic photos.

PURPOSE To compare optic disc measurements achieved by slit-lamp funduscopy, Heidelberg Retina Tomography II (HRT II), and stereoscopic optic nerve photos (SONP) in glaucomatous, ocular hypertensive, and normal eyes. METHODS A total of 176 eyes (glaucomatous [n=87], ocular hypertensive [n=40], and normal eyes [n=49]) of 90 participants were studied. Each participant underwent a full ophthalmic examination, including automated perimetry, slit-lamp funduscopy, HRT II, and SONP. To compare the three different methods being investigated, the following measurements were used: vertical cup to disc ratio (VCDR), horizontal cup to disc ratio (HCDR), and cup to disc area ratio (CDR). Slit-lamp funduscopy was evaluated only with respect to VCDR. HRT II and SONP were evaluated with all three measurements (VCDR, HCDR, and CDR). RESULTS CDR measurements in ocular hypertensive eyes did not differ significantly according to the measurement methods used (p=0.4). CDR in the other groups of participants, as well as VCDR and HCDR, all differed significantly within each group according to the method used (p<0.05 for all). Mean VCDR measured with funduscopy was smaller than mean VCDR measured with either HRT II or SONP in the glaucoma and ocular hypertension groups (p=0.0001). However, overall, the three methods showed a strong correlation in terms of VCDR, HCDR, and CDR measurements. CONCLUSIONS Despite the correlation among the three methods, the significant differences between their measurements of optic disc parameters may be too large for these methods to be used interchangeably in clinical situations.