Retinal thickness at the posterior pole in glaucoma and ocular hypertension

Ganglion cells with nerve fibre layer contribute a substantial fraction to the retinal thickness (RT). In contrast to the analysis of papillary and peripapillary area, which have shown large variability in normal eyes, the variation of retinal cell density in the perifoveal region is reported to be less than 10%. By measuring RT at the posterior pole we wanted to detect retinal changes due to glaucoma and determine their correspondence with visual field (VF) changes.

The Retinal Thickness Analyzer (RTA) was used to obtain RT maps in 21 normal eyes, 20 eyes with ocular hypertension and 22 eyes with glaucoma. A green laser slit (540 nm) of the RTA was focused on the retina at an angle and its intersection with the retina was imaged. The distance between the reflections from the vitreo–retinal and retina–retinal pigment interface is directly proportional to the RT. Five locations covering the central 20° were scanned, generating 10 optical cross sections that were transformed into colour-coded RTA maps. Numerical data were presented for the perifoveal and posterior pole region.

In glaucomatous eyes significant localised thinning of the retina was present, identified as the increased number of clusters including at least four points that are 2 standard deviations below normal. The minimum retinal thickness was decreased in glaucoma eyes and the perifoveal temporal modulation and perifoveal temporal/nasal asymmetry—indicators of greater RT loss in the temporal and the nasal quadrant, respectively—were higher in eyes with glaucoma, but with overlapping global indices between the groups. In 16 of 22 eyes with glaucoma there was good agreement of RT changes with VF defects. In two eyes with typical glaucomatous damage at the optic disc but without VF defects localised changes of RT were detected.

The RTA enables objective noninvasive evaluation of the posterior pole and could become helpful in diagnosis of glaucoma before the onset of functional damage. However, at present its clinical usefulness is limited by overlapping values of retinal thickness between normal and glaucomatous populations.