Analysis of Vision and Eye Movements by Scanning Laser Ophthalmoscope (SLO)
Current
This line of research could be implemented only because of an inherited donation from Ms. Beatrice Brandes. Her generosity allowed me to buy a precious instrument, a scanning laser ophthalmoscope (SLO), that tells us what is happening on someone’s retina while they are looking at a controllable target. Thus, the resulting video sequences show the retina AND the physical stimulus simultaneously. An example is the image below.
Legend picture 1: The picture shows the retina of a healthy young subject with the optic nerve head on the left and branches of blood vessels emanating from it. It also shows a cross overlaid on the center of the retina (the fovea) that the subject currently fixates.
We use the SLO in three different ways:
A. Development of modern micro-perimetry software
Traditional techniques used to find out which spots on the retina have intact light perception have been slow, inaccurate and too dependent on involuntary eye movements. We have changed that by developing software that knows when and where the eye has moved, so that the stimulus placement is automatically adjusted accordingly. This has made the procedure of micro-perimetry easier, shorter and more reliable. The “Smart Micro-Perimetry” (SMP) software is commercially available (For more detail, see www.macularmapping.com).
Publication:
MacKeben M & Gofen A. (2007) Gaze-contingent display for retinal function testing by scanning laser ophthalmoscope. J Opt Soc America A, vol. 24/5, May, pp. 1402-1410 (feature issue on “Retinal Imaging”) (pubmed).
Abstract
To overcome the inconvenience and imprecision of conventional software performing microperimetry with the Scanning Laser Ophthalmoscope (SLO) in clinical settings, we developed a “smart micro-perimetry” program. It takes advantage of modern computer technology, especially processing speed and high rate of data transfer. It allows continuous on-line processing of the image of the retina and instantaneous correction of stimulus placement according to involuntary eye movements. Thus, the program provides gaze-contingent display of the stimulus and senses the conditions for image tracking, so that stimulation during large eye movements, blinks and temporarily flawed image quality can be prevented. These features have greatly increased the efficiency and precision of SLO data in comparison to those obtained by older programs.
B. Performing micro-perimetry on patients with low vision
This is a collaborative effort with Donald C. Fletcher, MD, the director of the Low Vision Service at California Pacific Medical Center in San Francisco. Patients from Dr. Fletcher’s office are tested in routine way using our software in an otherwise identical set-up. Most of the tested patients suffer from age-related maculopathy.
The goal is to test whether light perception in any spot on the retina is still intact or damaged. The results are “maps” of the retina indicating by colored dots where test stimuli have been applied and whether they were seen (see image below: green = good, red = bad). Important is here what the patients can learn about their own gaze behavior that can help optimizing their remaining vision.
Legend picture 2: Like picture 1, this image shows the retinal of a human subject. In this case, it is a 75 year old woman who suffers from age-related maculopathy (ARM). The bold cross in the upper half indicates which retinal location she uses to fixate. Green dots indicate where briefly flashed dots of light were delivered and seen, red dots show where they were not seen. Note the accumulation of red dots representing a central “scotoma” (a blind spot).
C. Monitoring eye movements in low vision patients
The goal of this research is to measure eye movements while the patient solves a perceptual task. This could, for instance, be the “find-and-identify” task highlighted before (link to "Macular Search", this website). It is of special interest to us whether certain eye movement “strategies” allow solving the task faster and more efficiently.
This is work in progress.