Pre-refraction procedures, such as the measurement of vision or visual acuity and cover testing, are usually performed before the optimum refractive correction is determined. When patients habitually wear spectacles these procedures are conducted with the patient wearing those spectacles, if they have brought them to the examination. Where a patient does not have spectacles these procedures are conducted without any refractive correction in place. When patients wear spectacles for some visual tasks but not others some procedures may need to be done with spectacles and others without.
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. Whe...
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.
The cover test is used to elicit the presence of heterotropia, heterophoria, orthotropia or orthophoria. It allows the direction of the deviation (horizontal, vertical, torsional or combination) to be determined and also whether it is unilateral or alternating, constant or intermittent and the ef...
The cover test at near is used to elicit the presence of a heterotropia, heterophoria, orthotropia or orthophoria for near fixation targets.
Measuring eye deviation using the alternating cover test and prism bar. One or other eye is always covered during the test. To elicit the presence or absence of a heterophoria along with type of deviation (eso-, exo-, hyper- and cyclophoria), effect of refractive correction, accommodation and CHP...
The near point of convergence is the point where visual axes intersect under maximum convergence effort while binocular single vision is maintained. Some practitioners measure the near point of convergence routinely, but especially when a patent presents with near vision symptoms.
This is a measure of the maximum amount of accommodation an individual can exert. It can be described as the dioptric distance between the near and far points of accommodation and is usually measured using the RAF rule. It should be conducted monocularly and binocularly and may be repeated two or...
The measurement of stereoacuity is important as it gives an indication of the integrity of the binocular visual system. When the level of stereoacuity is within expected ranges then normal motor and sensory function are present. It is particularly useful for evaluating binocular vision in childre...
It is useful to test oculomotility (smooth pursuit eye movements) for a whole range of reasons but in particular when a patients presents with diplopia, there are symptoms such as eye pain when looking away from the primary position of gaze and when there is a reading difficulty which is unlikely...
The alternating cover test in the primary position allows comparison of the primary and secondary angles of deviation. Repeating the alternating cover test in the extreme positions of gaze will cause the size of the dissociated deviation to increase in the direction of the affected muscle(s).
