Vision screening in the Southern and Tairawhiti DHBs: An audit of the B4 School Check

Abstract

Amblyopia, or ‘lazy eye’, describes visual impairment occurring due to abnormal cortico-visual development as a child, and is the most common ophthalmological condition in children. The critical period for visual development in the human extends from birth to the around the ages of 7-9 years, and the development during this time occurs competitively between fellow eyes. Thus, any impairment in retinal image quality, neuronal function or misalignment of the eyes can lead to neuronal suppression of an eye, which may cause impaired visual acuity of that eye. Amblyopia can lead to issues later in life, such as limitation of occupational choices, poorer functional vision if something happens to the better-seeing eye, and an increased risk of vision loss in the better eye compared to individuals without amblyopia.

Amblyopia treatment is effective, however, so long as it occurs before the critical period of child cortico-visual development, and so, many societies have some form of child vision screening, so that children with amblyopia can be treated whileeffective treatment is still an option. In 2008, a nationwide screening programme was introduced in New Zealand: the B4 School Check (B4SC), and, currently, there is little data regarding the efficacy of the vision screening portion of the B4SC. This study primarily aimed to assess the accuracy of the B4SC vision screening, by determining the positive predictive value, negative predictive value, sensitivity, and specificity of the programme. This was done by collecting data regarding visual acuity and referral status for all children screened by the B4SC within the Southern and Tairawhiti DHBs, and cross-matching this to data collected regarding these children who also presented to community optometrists and DHB eye clinics in the Southern and Tairawhiti DHB regions for comparison. This study found that the positive predictive value for the B4SC was 53.5%. The negative predictive value was found to be between 96.1 and 99.9%, sensitivity was between 35.3 and 95.1%, and specificity was between 93.5 and 97.0%. It found that visual acuity testing is accurate, while it does have a low positive predictive value, the screening is performing its function of identifying cases of reduced visual acuity, without missing many cases.