The progression of keratoconus is commonly determined by comparing the results of corneal tomographic measurements on different occasions. However, investigations on the repeatability of measurements are commonly performed within the same day, thus not taking the inter-day variation into account. The effect of keratoconus disease severity on the measurement error is also seldom considered. In this post hoc investigation, the parameters A, B and C in the Belin ABCD Progression Display were evaluated in relation to disease severity in intra-day and inter-day measurements. Four consecutive measurements were performed on 61 patients with keratoconus on the same day (intra-day). In another cohort, four consecutive measurements were obtained and then repeated 3 days later in 25 patients with keratoconus and 25 healthy controls (inter-day). The results suggest that the diagnosis of disease progression would benefit from inter-day measurements, and the stratification of the parameters A and C according to disease severity. It is also recommended that tomographic systems such as the Pentacam HR be modified to allow the comparison of both single measurements and the mean of replicate measurements of the parameters used in the assessment of progression of keratoconus.

Background: Amblyopia is the most common monocular visual impairment in Scandinavia. A visual screening programme for preschool children was introduced in Sweden in the 1970s to reduce the prevalence of amblyopia. The purpose of this study was to investigate the impact of this visual screening programme in adult men recruited to the armed forces in Sweden. Methods: The prevalence of amblyopia was compared in recruits born in 1956-1957 (n = 1500), before the introduction of the visual screening programme (unscreened), and those born in 1977-1979 (n = 2626), after the visual screening programme was introduced (screened). Amblyopia was defined as bilateral, if the bilateral best corrected visual acuity (BCVA) was <0.5 (20/40), and unilateral if there was a ≥2-line interocular difference and BCVA was <0.625 (20/32) in the worse eye. Subgroup analysis was performed on recruits with hyperopia, myopia and anisometropia. Results: The prevalence of amblyopia was significantly lower after the introduction of the Swedish visual screening programme. Forty-seven (3.3%) of the unscreened and 23 (0.9%) of the screened recruits had unilateral amblyopia (p < 0.0001, OR = 0.26 (95%CI 0.16-0.43)). The risk for developing amblyopia was markedly reduced by screening in recruits with hyperopia (≥2D) (p < 0.0001 and OR 0.034 (95% CI 0.003-0.207)) and anisometropia (≥1.5D interocular difference) (p < 0.01 and OR 0.20 (95% CI 0.08-0.66)). Only a few recruits with myopia had amblyopia. Conclusions:The results demonstrate the value of the Swedish visual screening programme for preschool children in preventing amblyopia. Anisometropia or high hyperopic refractive errors can be identified by screening and corrected to prevent amblyopia.