Fixation behavior and reading ability in macular scotoma: Assessed by Tuebingen manual perimetry and scanning laser ophthalmoscopy

The aim of this study was to compare fixation results assessed by Tuebingen manual perimetry (TMP) and scanning laser ophthalmoscope (SLO) and to examine the significance of fixation behavior for the reading ability in macular scotoma (37 eyes). Kinetic TMP was performed with special attention to the location of the central scotoma and the blind spot. Retinal fixation locus (RFL) was determined for single targets, words of different length and size as well as text using a modified SLO. Eye movements and RFL during reading were recorded simultaneously on videotape. In TMP, eccentric fixation was found in 78% of eyes, 93% of them showed a preferred direction of scotoma shift to the upper and upper-right visual field. With the SLO, eccentric fixation was observed in 86% of eyes, 96% of them had the preferred RFL in the the upper and upper-left retina. In three eyes with incomplete absolute central scotoma the RFL depended on stimulus size. Eccentric fixation is an effective adaptive mechanism for regaining reading ability in macular scotoma and indicates cortical plasticity. Complete absolute central scotoma is the best precondition for the use of one eccentric RFL. A remaining central island causes alternate RFL and explains discrepancies between visual acuity and reading ability. TMP and SLO results show a high correspondence. SLO has the advantage of quick determination of the RFL, of detecting alternate RFL, and of simultaneous assessment of morphologic, sensory, and motoric aspects during reading.