Work

Metamorphopsia and interocular suppression in monocular and binocular maculopathy

Year: 2014

Type: article

Abstract: Metamorphopsia is a key symptom of macular disease, particularly age-related macular degeneration (AMD) (De Jong 2006), that is often measured with Amsler grids at home and in the clinic, even though the test lacks both sensitivity and specificity (Schuchard 1993; Crossland & Rubin 2007). We address issues of monocular viewing and fixation compliance with a computerized version of the Amsler grid and binocular eye-tracking. Control of monocular viewing and compliant fixation enabled accurate quantification of the area and location of metamorphopsia in each eye. An eight-item questionnaire was administered to assess metamorphopsia patient reported outcomes (Alster et al. 2005; Arimura et al. 2011), and we measured interocular suppression with a dichoptic task with stereo shutter glasses. All participants were recruited with the criterion of no reported foveal vision loss and binocular calibration was used to track either eye monocularly. Those not accurately tracked were excluded from the study. Of the 74 macular disease patients who viewed the Amsler grid monocularly with each eye, 95% (70/74) experienced distortion in at least one eye, and 27% (20/74) experienced distortion in both eyes. Of the 34% (25/74) of participants diagnosed with binocular macular pathology, 80% (20/25) perceived distortions in each eye. Despite this high prevalence, most patients report no impact of distortion on the metamorphopsia questionnaire (Fig. 1A), and the overall area of the Amsler grid affected by distortion was not correlated with the score. There were no differences between total metamorphopsia score across the nine disease groups (see Fig. 1B). Participants with foveal distortion in both eyes (25%, 18/74) had a significantly higher score (3.7) than those who experienced metamorphopsia in only one eye (1.9), (p = 0.04, nonparametric Mann–Whitney U-test, Fig. 1C left). We also found a significant correlation with LogMAR acuity in the affected eye and the total metamorphopsia questionnaire score (r = 0.189, p = 0.031). In a post hoc analysis, an assessment to detect interocular suppression was administered to 49 of 74 participants who reported distortion in only one eye with our computerized Amsler grid. A nonoverlapping circle and cross were presented to each eye dichoptically with stereo shutter glasses. Suppression was classified when observers were unable to perceive both targets simultaneously even when the unseen target was moved. We found robust suppression of the affected eye in 59% (29 of 49) of monocular participants, and those who did not suppress scored higher (2.5) on the metamorphopsia questionnaire than those who did suppress (2.2), but not significantly so (p = 0.3, Fig. 1C right). Thus, distortions must be foveal and binocular to be noticeable in everyday life since monocular distortions are often suppressed by a less impaired eye. This lack of awareness may be critical when distortion is used as a screening and progression-monitoring tool or as a postoperative outcome measure (Jensen 1998; Wang et al. 2005; Wittich et al. 2005), especially given the importance of self-referral for AMD. Our findings should warn patients and clinicians against a false sense of security when the progression of monocular vision pathology seems stable when assessed with Amsler grids or patients reported outcomes that may be (self-) administered binocularly. In these cases, the patient may not be aware of spatial distortion in everyday activities, and hence fail to report pathological vision impairment to a clinician.

Source: Acta Ophthalmologica

DOI: 10.1111/aos.12559

Authors: Emily Wiecek, Kameran Lashkari, Steven C. Dakin, Peter Bex