Instrument based vision screening is an alternative vision screening method to detect the risk factors for amblyopia, which include strabismus (a misalignment of the eyes in any direction), media opacities (e.g., cataracts), and refractive errors (e.g., myopia, hyperopia, astigmatism, presbyopia). It consists of photoscreening and autorefraction.
Photoscreening is a technique that uses the principle of photorefraction, in which the refractive state of the eye is assessed via the pattern of light that is reflected through the pupil. In photoscreening, optical images of the eye’s red reflex to estimate refractive error, media opacity, ocular alignment, and other factors, such as ocular adnexal deformities (e.g., ptosis), all of which put a child at risk for developing amblyopia. Performed in a darkened room, photoscreening requires little cooperation from the individual, other than fixating on a target for the duration of the screening process. Images of the pupillary reflexes (autonomic reflex constrictions caused by light) and red reflex (a circular red light reflected from the retina of the eye) are obtained. The photographs can then be analyzed by the evaluator or sent to a central laboratory for analysis by an ophthalmologist or specially trained personnel. Test results are typically graded as pass, fail, or if the procedure must be repeated if results are equivocal.
Autorefraction is a technique that uses several types of automated methods (e.g., optically automated skiascopy or wavefront technology) which evaluate the refractive error of each eye. Data from autorefraction yield numeric results that are analyzed by the evaluator or by the instrument itself to determine if a child passes or fails the screening.