Dysfunction of the afferent visual system, characterised by impairments in high-contrast visual acuity (HCVA) and low-contrast visual acuity (LCVA) have been demonstrated in some neurological conditions such as multiple sclerosis and Parkinson’s disease. HCVA and LCVA are also potential quantitative markers of neurological dysfunction in amyotrophic lateral sclerosis (ALS). These afferent visual systems are not routinely tested in neurology settings, in the main due to the complex nature and duration of gold standard (GS) acuity testing protocols. The authors used this study to compare simplified gold standard visual acuity protocols. Monocular HCVA and LCVA were measured in patients with ALS (n=10) and four healthy controls, using six protocols, varying by two chart and three refraction methods. Results showed that interclass correlation coefficients between simplified and GS protocols ranged from 0.83 to 0.98 (HCVA – showing excellent agreement) and 0.56 to 0.75 (LCVA, showing moderate agreement). Differences between LCVA and GS protocols exceeded test-retest reliability. Simplified HCVA protocols using LCD tablet charts and / or pinhole correction produced valid measurements. However, none of the modified LCVA testing protocols produced valid measurements. The results of this study support the use of LCD tablets to display charts and use of pinhole to correct refractive error for HCVA measurement only in patients with ALS. Additional research using a larger sample is needed to validate the modified HCVA protocols and to develop simplified LCVA protocols.
Development of testing protocols for high and low contrast visual acuity
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