Binocular fixation topography in patients with diabetic macular oedema

Background: During retinal photocoagulation for diabetic maculopathy there is a potential risk of foveal burns, and laser scars may later enlarge to be sight-threatening when involving retinal areas previously used during fixation. Since the retinal area used during binocular steady fixation has been found to vary considerably in the normal test person and central fixation may be even further compromised in patients with diabetic maculopathy, the sight-threatening side effects could possibly be reduced by taking into account the fixation area individually. However, no study has described and quantified the retinal area of fixation binocularly in patients with clinically significant macular oedema (CSME). Methods: Sixteen diabetic patients with CSME in one or both eyes were examined. Each examination included visual acuity testing (ETDRS charts), a standard eye examination, central retinal thickness assessment by optical coherent tomography, fluorescein angiography and binocular quantification of fixational eye movements using an infrared recording technique. Results: A negative correlation was found between visual acuity and mean microsaccadic amplitude (R=0.48, p=0.009). The maximal retinal extension of the fixation area ranged between 1.0 degrees and 3.0 degrees, and in two eyes with CSME, this area was estimated to exceed 800 mu m on the retinal plane. No correlation was found between retinal thickness and visual acuity, retinal area of fixation, maximal extension of the fixation area or mean microsaccadic amplitude. Conclusion: Large interindividual differences in quantitative measures of binocular fixational eye movements were found. The mean amplitude of fixational eye movements was not correlated to central retinal thickness, and fixation area could only partly be predicted by visual acuity. Two eyes with CSME had an estimated maximal extension of the fixation area exceeding the central 800 mu m on the retinal plane; thus, the possible benefit of individualising central photocoagulation according to precise measures of fixation area needs to be investigated on a larger population.