M D Crossland¹, L E Culham², S A Kabanarou¹, G S Rubin¹
¹Institute of Ophthalmology, University College, Vision Rehabilitation Research, London, United Kingdom; ²Moorfields Eye Hospital, Optometry Department, London, United Kingdom
Fixation stability and visual behaviour in macular disease have traditionally been assessed using the Scanning Laser Ophthalmoscope (SLO). However the SLO can only produce relatively simple, monochromatic stimuli, the target viewing distance is fixed and the patient's head needs to be rigidly secured. In our laboratory we have used an infra-red eyetracker to assess patients' fixation behaviour when viewing letters, sentences and more complicated images such as faces.
We compare and contrast the use of an SLO (Rodenstock, Germany) and the eyetracker (SensoMotoric Instruments Gazetracker, Germany) as techniques for investigating fixation position, fixation stability and saccades in normal subjects and patients with macular disease.
We have found a linear relationship between fixation stability measurements made using the SLO and the eyetracker for normal subjects (r=0.92), although fixation as assessed by the eyetracker is less stable than SLO recordings indicate. It is assumed that this is due to the free-head nature of the eyetracker. For more complex images, the eyetracker is superior in terms of stimulus presentation and data analysis. However the retina cannot be imaged with the eyetracker.
We believe that the eyetracker is a useful adjunct to the SLO in investigating visual behaviour in macular disease.
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