Abstract
Purpose: :
To evaluate the relation of spherical and cylindrical anisometropia (ANISO) with the presence of amblyopia, interocular acuity difference (IAD) and stereoacuity (SA), among Head Start Preschoolers.
Methods: :
3- to 5-year old non-strabismic children (n=3894) underwent monocular VA testing (Electronic Vision Tester), stereoacuity testing (Random Dot E or Stereo Smile test) and cycloplegic refraction. VA in both eyes was tested while wearing spectacles for children with spectacles, and was retested with full cycloplegic correction when (1) VA <20/50 for 3-year-old, VA <20/40 for 4- to 5-year-old or child showed an IAD ≥ 2 lines; AND (2) hyperopia ≥ 2.0 D, myopia ≤ -0.5 D, or astigmatism ≥ 1.0 D was present in either eye. Unilateral AMBLY was defined as IAD ≥2 LogMAR lines. Refractive error was classified into three mutually exclusive groups: (1) isometropic (ISO): inter-eye difference of spherical equivalent (SE) < 0.25D and of cylinder < 0.25D; (2) SE ANISO: SE difference ≥0.25D and greater than inter-eye cylinder difference; (3) cylinder ANISO (C ANISO): cylinder difference ≥0.25D and greater than SE difference. Children with ANISO were further grouped based on amount of ANISO. The percentage with AMBLY, mean IAD and mean SA in ANISO groups were compared to those in ISO.
Results: :
Compared with ISO children (n=1163), ANISO children (n=2565) had higher percentage of AMBLY (8% vs. 2%), larger IAD (0.07 vs. 0.05 LogMAR) and worse SA (145 vs.117 arc sec) (all P<0.0001). For SE ANISO (n=1214) and C ANISO (n=1284), higher degrees of ANISO are associated with higher percentages of AMBLY, larger IAD and worse SA (trend p-values <0.0001). Compared with ISO (2% with AMBLY, 0.05 logMAR in mean IAD), the percentages with AMBLY and mean IAD are significantly higher when SE ANISO is 0.5-0.75D (10% with AMBLY, 0.07 logMAR in mean IAD), 0.75-1.0D (19%, 0.11), 1.0-1.75D (21%, 0.11), and >1.75D (48%, 0.24); or when C ANISO is 0.25-0.5D (6%, 0.06), 0.5-1.0D (11%, 0.08), 1.0-1.5D (29%, 0.13), and >1.5D (34%, 0.19).
Conclusions: :
The presence and amount of SE or C ANISO are associated with increased risk of amblyopia, larger IAD and worse SA. Increased risk of amblyopia among preschoolers occurs when SE ANISO ≥0.5D or C ANISO ≥0.25D.
Keywords: amblyopia • refraction • clinical (human) or epidemiologic studies: risk factor assessment