Low-contrast visual acuity versus low-luminance visual acuity in choroideremia

Area of Science:

• Ophthalmology
• Genetics
• Retinal Diseases

Background:

• Choroideremia is a progressive X-linked inherited rod-cone dystrophy.
• Patients experience nyctalopia and progressive visual field loss, with visual acuity often preserved until later stages.
• This limitation hinders the use of standard visual acuity as a clinical trial endpoint across the disease spectrum.

Purpose of the Study:

• To assess the utility of low-luminance visual acuity (LLVA) and low-contrast visual acuity (LCVA) as clinical trial endpoints in choroideremia.
• To determine if these tests can identify functional deficits earlier than standard high-contrast visual acuity.

Main Methods:

• Evaluated 29 choroideremia subjects and 16 healthy controls using logMAR charts.
• Measured standard high-contrast visual acuity, LLVA (using a 2.0-log unit neutral density filter), and LCVA (at 1.25% and 2.5% contrast).
• Analyzed data using non-parametric statistics to compare groups and identify correlations.

Main Results:

• Choroideremia subjects showed significantly poorer performance on LLVA and LCVA compared to controls (p < 0.01).
• 1.25% LCVA demonstrated the poorest performance among the tested conditions.
• Strong positive correlations were observed between LLVA and high-contrast visual acuity (ρ = 0.818) and 2.5% LCVA and high-contrast visual acuity (ρ = 0.671).

Conclusions:

• LLVA may serve as a valuable additional outcome measure in clinical trials for early-to-moderate stage choroideremia.
• These tests can detect visual function changes when high-contrast visual acuity remains relatively preserved.
• LLVA and LCVA offer potential for earlier detection of disease progression in clinical trials.