A thorough examination should be completed to include measurement of heterophoria/heterotopia (ocular alignment), vergence amplitudes and /or fixation disparity
, near point of convergence, amplitudes of accommodation, accommodative facility, and assessment of saccadic function.
As previously investigated by other researchers [35-37], we could expand our current analyses based on an objective eye tracker method with additional calculations of fixation disparity
at the end of the vergence step response.
Hoya said that the second is a complete vision examination system with a new method to detect and correct fixation disparity
He was also found to have astigmatism (a rugby ballshaped cornea) and a fixation disparity
, which means he had problems focusing his eyes together.
People with more exo fixation disparity
at 40 cm tend to experience asthenopic complaints and visual fatigue when doing visual near work (Evans, 1997 ; Pickwell, Kaye, & Jenkins, 1991; Scheiman & Wick, 1994; Sheedy & Saladin, 1983).
Similarly, during the eye examination practical, I believe that it is important to perform complete preliminary tests, including motility, and following refraction assess binocular vision with the new prescription using fixation disparity
, or a comparable method if appropriate.
A steady-state error known as fixation disparity
is often present when maintaining vergence in a closed-loop environment (Schor, 1980).
* Check each eye can resolve the fixation disparity
However, sometimes, despite a very thorough refraction and examination using fixation disparity
tests, the cause of what at first appears to be an eye-related problem can be elusive.
With many of the binocular vision tests included with the Thomson Test Chart 2016, optometrists can perform stereopsis tests (although this could be improved), phoria tests and fixation disparity
tests with ease.
Orthoptists do not refract or measure fixation disparity
(sensory fusion) or understand the physiology of normal binocular vision, which is intimately related to the accommodation vergence reflex.
These systems comprise diagnostic programs to assess phorias, fixation disparity
, fusional vergences and suppression, motor fields, pursuits and saccades, while therapeutic programs provide tasks to treat ocular motility, vergence and accommodative disturbances.