Evaluation of fixation pattern and reading ability in patients with Leber hereditary optic neuropathy

Leber hereditary optic neuropathy (LHON) is characterized by progressive loss of central vision leading to impaired reading ability. The aim of this study was to evaluate sensory adaptation and reading ability in LHON patients.

This prospective pilot study included 12 male patients with a clinical diagnosis and a positive genetic analysis of LHON, who matched the inclusion criteria of a central scotoma on visual field testing and the use of magnifying aids to read. Examination included best-corrected visual acuity, magnification need, reading speed, and evaluation of fixation by corneal reflexes and by Rodenstock scanning laser ophthalmoscope (SLO). Central scotoma was assessed by conventional perimetry (Tübingen Automated Perimeter) and microperimetry (NIDEK MP1).

Mean magnification need was 13.2 ± 7.3-fold (range: 2- to 25-fold). Mean reading speed was 53 ± 18 words per minute (WPM) (range: 24-85 WPM). With automated perimetry, all patients showed central scotomas with a mean radius of 13° ± 7° (range: 1°-30°) in the better eye. Microperimetry in all patients showed fenestrated central scotomas. Eccentric fixation with a preferred retinal locus (PRL) was detected with SLO examination and microperimetry correlated well in 11 of 12 patients. The SLO results showed no systematic pattern in the placement of the PRL; however, 7 of 12 patients (58%) placed their PRL in an unfavorable location left or below the fovea. In 8 of 12 patients, fixation was unstable. Between reading speed and central scotoma size, there was a statistically significant negative correlation (P = 0.021, r = -0.65).

The percentage of unfavorable PRL locations was extremely high compared with other disorders with central scotomas. Unstable fixation and fenestrated central scotomas led to difficulties in reading. Early rehabilitation and, if necessary, eccentric viewing training should be considered in LHON patients.