Scanning Eye Movements in Homonymous Hemianopia Documented by Scanning Laser Ophthalmoscope Retinal Perimetry

Abstract

Sparing or partial recovery of visual fields in hemianopic patients is frequently difficult to document. This is because when testing large field losses, the standard automated or manual visual field testing systems have limited fixation controls. Measured visual field recovery in these cases may not be real but instead may be due to an artifact such as scanning eye movement. This article illustrates a way to separate the actual visual field sparing from scanning eye movement artifact by using perimetry testing with the scanning laser ophthalmoscope (SLO). During the SLO perimetry, the examiner has a direct and magnified view of the retinal fixation locus. This direct view allows for the added ability to monitor the fixation stability during target presentation. When eye movements larger than 1 degrees are noted, the examiner can repeat the trial. During static perimetry, our SLO records the retinal position of the fixation target at the end of the stimulus presentation and corrects scanning eye movements that occur during stimulus presentation. These special features enable us to identify when the apparent sparing of the visual field is due to the artifact of scanning. To demonstrate this, we selected the records of four hemianopic patients whose fields were examined by both standard perimetry and the SLO. We then compared the clinical visual fields with the SLO perimetry fields. One of the patients had a complete homonymous hemianopia on both the clinical perimetry and the SLO perimetry. A second patient was found by the SLO to have unstable fixation during testing. The SLO perimetry revealed that the apparent spared fields seen in standard perimetry were the result of eye scanning and not an actual enlargement of the visual field. Two other patients were confirmed by the SLO findings to have valid partial recovery of the visual field, one with and one without scanning eye movements. The advantages and limitations of SLO perimetry in analyzing hemianopic field sparing are discussed.

Combined use of SLO microperimetry and OCT for retinal functional and structural testing

“…During the SLO microperimetry examination, a cross-shape fixation target and Goldman-like static targets were presented to the patients. The perimetry stimuli used in SLO testing were square rather than circular, compared to conventional perimetry, but the sizes of 4, 8 and 32 pixels width are approximately equal to Goldman II, III, and V, respectively [7]. First, all patients were tested for dense scotomata with a stimulus intensity of 10,000 Trolands (Td).…”

“…First, all patients were tested for dense scotomata with a stimulus intensity of 10,000 Trolands (Td). The maximum stimulus intensity available in SLO microperimetry is 10 times lower than the maximum intensity in Humphrey and Goldmann perimetry [7]. Secondly, all patients were tested for relative scotomata with a stimulus intensity of 300 Td, which represents the lowest stimulus intensity usually seen by healthy subjects.…”

“…It allows the examiner to observe an image of the retina illuminated by a 790 nm infrared laser light source while stimuli created by a 633 nm HeNe laser are superimposed on the retina. These superimposed stimuli are used to provide fixation targets and static perimetry targets of adjustable sizes, shapes and intensities [7].…”

Clinical treatment options for patients with homonymous visual field defects

“…This is because the claims of significant field increases found in the VRT studies mentioned above were based on a method of assessing the visual field which was incorporated into the training device and did not allow a reliable way of controlling the patients’ fixation. The effect of VRT has been re-evaluated using techniques which allowed a much more reliable means of monitoring the patients’ fixation, specifically the use of a scanning laser ophthalmoscope (SLO; Jamara et al 2003) combined with microperimetry. In studies whereby they reliably monitored fixation during visual field assessment no significant visual field increases were obtained (Sabel et al 2004; Reinhard et al 2005; Schreiber et al 2006).…”

Low vision rehabilitation and driving training for hemianopic visual field loss: two case reports

“…The impact of non-driving has been shown to negatively impact quality of life by restricting independence and increasing social isolation [2]. 0531 VF awareness may be enhanced with prisms and scanning training despite the fact that actual visual field cannot be restored [3][4][5]. Patients prescribed prisms for pedestrian navigation and driving have demonstrated some functional improvement in specific visual and mobility tasks [6].…”