Low-contrast acuity measurement: does it add value in the visual assessment of down syndrome and cerebral palsy populations?

PURPOSE

Children with Down syndrome (DS) and cerebral palsy (CP) often have reduced visual acuity (VA). This study assessed VA and low-contrast acuity (LCA) with Lea symbols in DS and CP populations to explore whether LCA measures provide useful additional information about visual performance. VA and LCA were also measured in a large group of typically developing young people.

METHODS

High-contrast VA and LCA performance was measured monocularly using crowded Lea symbols with 45 young people with CP (mean age 11.8 ± 4 years), 44 with DS (mean age 10.5 ± 3 years), and 211 controls (mean age 11.4 ± 3 years). Refractive status was confirmed with cycloplegic retinoscopy.

RESULTS

DS AND CP GROUPS HAD SIGNIFICANTLY LOWER ACUITIES THAN CONTROLS AT ALL CONTRASTS (P 0.001). MEAN (SD) HIGH-CONTRAST VA WAS AS FOLLOWS: DS = +0.39 ± 0.2 logMAR; CP = +0.18 ± 0.2 logMAR; controls = -0.04 ± 0.1 logMAR. Mean 2.5% LCA was as follows: DS = +0.73 ± 0.2 logMAR; CP = +0.50 ± 0.2 logMAR; controls = +0.37 ± 0.1 logMAR. For controls, the mean difference between VA and 2.5% LCA was 0.40 logMAR (95% limits of agreement, ± 0.22 logMAR). While there was a positive relation between VA and 2.5% LCA scores (linear regressions, P < 0.0001), considerable variation existed, with VA explaining only 36% of the variance in LCA performance for control data.

CONCLUSIONS

VA and LCA performance was significantly poorer in DS and CP groups than in controls, and high-contrast VA did not reliably predict low-contrast performance. Therefore both high- and low-contrast acuity assessment are valuable to fully describe an individual's visual function, and this may be particularly relevant in DS and CP in cases in which patients are unable to articulate visual difficulties. Age-specific reference data from a large sample of typically developing young people across a broad age range are presented for clinicians using high- and low-contrast Lea symbols.