Scanning laser polarimetry (SLP) for optic nerve head drusen

Optic nerve head drusen (ONHD) are either clinically invisible or clearly protruding from the disc, in the later case leading to the condition of an irregular, indistinct disc margin or a swollen disc on biomicroscopy. They also may cause visual field defects, even with slow progression. Scanning laser polarimetry (SLP) has been proposed as a rapid, objective and reproducible technology for retinal nerve fiber layer (RNFL) assessment and clinical studies have demonstrated that SLP can help to distinguish between normal and glaucomatous eyes, identify glaucoma suspects and correlates well with visual field defects. The purpose of this study was to evaluate the potential applicability of SLP in 20 consecutive patients with optic nerve head drusen (18 bilateral) that were clinically visible (22 eyes) and invisible (16 eyes). RNFL thickness was studied in patients with and without visual field defects. Patients with visual field defects and ONHD were significantly older and had a small, but significant reduction of visual acuity. Some global SLP parameters (average thickness, ellipse average) were significantly different between subjects with normal and abnormal visual fields. The comparison of the groups with visible and invisible drusen showed that there was no difference in demographic or perimetric data. RNFL thickness measurements were also very similar in both groups. Clinical visibility of drusen was not correlated with RNFL thinning as measured with the GDxTM. SLP assessment, however, was well correlated with functional loss. This objective, non-invasive technology may be an additional option for RNFL evaluation in this condition and an especially useful tool for long-term follow-up.