The small ring of dots lies over a graticule with standard axis notation reading from 0º to 180º anticlockwise. When a spherical lens is measured, the ring of dots will be blurred when out of focus, and crisp when in focus, at which point the power of the lens can be read off the power wheel. When an astigmatic lens is measured, the dots will be drawn out into two focal lines (at different powers). The power should be recorded twice (once for the sphere and once for the cylinder), at the positions at which the dots are drawn into the sharpest lines. For each power, there will be a corresponding axis, which can be read off the graticule.
The purpose of this test is to assess the symmetry of binocular fixation by comparing the brightness of the red reflex formed by the ophthalmoscope beam in each eye.
Useful in paediatric cases when the patient is not co-operative enough for a cover test, especially when the clinician needs to differentiate between pseudostrabismus and strabismus.
Assessment of pupil function can provide diagnostic information about the afferent and efferent neurological pathways responsible for pupillary and eyelid function.
