BACKGROUND: Afferent visual system disorders are included in the phenotypic spectrum Amyotrophic Lateral Sclerosis (ALS). High and low contrast visual acuity (HCVA and LCVA) are potential quantitative clinical markers of this dysfunction. Gold standard clinical research protocols for HCVA and LCVA measurements are difficult to implement in a neurology clinic. Pinhole is a possible substitute for refraction, which is time consuming requiring specialized equipment and personnel. Charts presented on tablets are a potential substitute for retro-illuminated charts, which are bulky and less readily available. The purpose of this study is to evaluate the effect of substituting pinhole for refraction and tablet charts for retro-illuminated charts on HCVA and LCVA in ALS patients.

DESIGN/METHODS: Monocular HCVA and 2.5% LCVA were measured at 2m in 8 ALS subjects using two chart conditions (retro-illuminated Sloan charts, iPad presented charts) and two correction conditions (spherical refraction, pinhole). Number of letters correctly identified was compared between chart condition and between correction conditions. Differences less than 5 letters (1 line) were considered comparable.

RESULTS: HCVA was comparable between correction conditions and between chart conditions for 6/8 (75%) and 7/8 (88%) subjects respectively. LCVA was comparable between correction conditions and between chart conditions for 3/8 (38%) and 6/8 (75%) respectively. In comparable values favored pinhole for HCVA and spherical refraction for LCVA.

CONCLUSIONS: In this pilot study, we find that HCVA and LCVA tablet presented charts produce comparable measurements to gold standard retro-illuminated charts in greater than 75% of ALS subjects. Pinhole correction is comparable to spherical refraction for measurements of HCVA but not LCVA. HCVA measurements with pinhole and tablet charts are less burdensome for ALS patients and research staff without sacrificing accuracy. Pinhole is not a suitable modification for LCVA measurements.

Summary Points:

  • Compared the King-Devick Contrast Acuity Chart to the retro-illuminated Sloan chart in patients with ALS.
  • High and low contrast visual acuity was comparable between the two chart types.
  • The K-D Contrast Acuity Chart demonstrated an accurate measurement of contrast acuity, with the benefit of both portability, illumination, and availability compared to retro-illuminated charts.
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