Abstract
Purpose:
To perform low cost fixation stability assessment and kinetic perimetry during live fundus viewing using the Digital Light Ophthalmoscope (DLO).
Methods:
Kinetic perimetry was performed on 12 undilated normal subjects aged 25 - 63 with real-time confocal retinal imaging using the DLO. Having similar functionality to a Scanning Laser Ophthalmoscope, but at far lower cost, the DLO uses a single digital light projector to provide both the illumination for confocal imaging, and the stimuli for visual function measurements. Confocal retinal imaging is performed at 20 Hz with a 35.1 deg field of view. The imaging illumination is provided by a red 630 nm LED, with 40 µW time-averaged power at the cornea. Stimuli are shown in black over the red imaging illumination and are operator controlled in shape and position in real-time. The black stimuli are easily seen by the subject and are also clearly visible on the live view of the fundus. Subjects were instructed to stare at a fixation target while a Goldman V size (1.72 deg diameter) target was presented near the optic nerve head. The path taken by the stimulus was guided by one of eight meridians that converged at a point on the optic nerve head. The meridians were equally separated by 45 deg, and 7 deg long. Each stimulus moved incrementally outwards, from “not seen” to “seen”, at approximately 2.5 deg per sec. Once the stimulus was seen by the subject, an 8 image frame buffer was saved. Fixation stability was separately measured by acquiring 60 frames over 3 sec while the subject fixated on a cross-hair target with 0.3 deg line thickness.
Results:
The stimuli were directly visible on the retinal image frames, providing precise visual function testing. The visual function maps, formed by registering and superimposing the fundus images obtained for each stimulus meridian path, agreed well with the boundaries of the optic nerve head. The subjects’ fixation was 0.25±0.13 deg, measured over a 2 sec blink-free interval of the 3 sec acquisition.
Conclusions:
The DLO with integrated visual function testing is a flexible and cost-effective platform for conducting image-corrected visual function tests, such as kinetic perimetry and fixation stability assessment, and can be readily extended to scotoma mapping and reading tests.
Keywords: 642 perimetry •
552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)