Abstract
Abstract: :
Purpose: Clinical assessment of the accommodation/convergence relationship is usually based on measurements of vergence for different accommodative demands, without measuring accommodation, leading to the 'stimulus AC/A ratio'. The 'response AC/A ratio' (Alpern et al., AJO, 1959), based on convergence and accommodation, may be more useful when studying risk factors for accommodative esotropia (accET). We explored a method for the assessment of stimulus and response AC/A ratios in infants and young children, and compare findings between patients with accET and normals. Methods: An eccentric infrared digital photoscreener (PowerRefractor®) was used to simultaneously measure binocular accommodation and convergence to accommodative targets at 0.3, 1.0, 2.0, 3.0 and 4.0 D in 32 normal children (age 3 mos â|*128*|" 8 yrs; median 15 mos) and 12 patients with accET (6 mos â|*128*|" 8 yrs; median 33 mos). In a subset of patients we also obtained measurements under monocular stimulation to compare disparity–driven and blur–driven responses. Results: In the normal group, stimulus AC/A was 4.1 ± 1.4 â|*136*|†/D and response AC/A was 3.3 ± 1.4 â|*136*|†/D; response AC/A was correlated with age (r = 0.36; P = 0.04) but stimulus AC/A was not. Of the patients with accET, 2 showed abnormally high stimulus and response AC/A ratios and 3 additional patients showed abnormally high response AC/A but normal stimulus AC/A. Findings in the other 7 patients were not different from the normals. Under monocular stimulation, patients showed much smaller AC/A ratios and little blur–driven convergence. Conclusions: This technique allows a detailed assessment of the relationship between accommodation and convergence in infants and young children. The observed age–effects in normals suggest that convergence is (close to) mature at an early age (around 3 mos), but accommodation not. More patients with accET appear to show abnormalities in response AC/A than in stimulus AC/A, suggesting that the mechanism for accommodation may be affected alongside their excessive convergence.
Keywords: infant vision • vergence • esotropia and exotropia