Normal Distance Phoria with a Normal AC/A
Sharpens retinal image and/or alters vergence of eyes; may lead to lessened suppression, enhanced sensory fusion, and stronger stimulus to fusional vergence.
Equally sharp retinal images more important than equal image sizes in anisometropia.
Disregard possible aniseikonia initially but prescribe equal base curves and center thickness in significant anisometropia prophylactically.
Fully correct anisometropia and/or astigmatism.
Base-out prism useful for all distance esophorias.
Base-in prism more useful in exotropia than exophoria.
Exo- deviations respond well to vision therapy in pre-presbyopes.
Vertical prisms should be prescribed for the vertical deviation present with eyes in "ortho" position.
Rx vertical prism in heterophoria based on associated phoria; even as little 1/2 p.d. may be helpful for fusion.
In paresis, Rx greater prism power before eye with paretic muscle.
What is the deviation at distance and near after neutralizing the refractive error? Added plus power at near for eso-deviations reduces the deviation according to size of the AC/A and power of the added lens.
Effective for suppression and amblyopia.
Complete occlusion better than graded.
Use two to six hours/day maximum to avoid "occlusion" strabismus.
Regimen should be specifically prescribed and monitored; for infants and young children, occlude preferred eye 1 day/week/year of age.
Six to 8 weeks is minimum period for initial occlusion and for continued occlusion beyond last measured improvement.
Two hrs/day is minimum time for effective occlusion.
These are usually anisometropic amblyopes with unsteady centric fixation.
Treat with acuity improvement program.
Stimulate fovea under monocular and BINOCULAR conditions (anti- suppression) to improve resolution and simultaneous perception.
Gradually decrease monocular target size and element separation.
Reinforce therapy with kinesthetic, auditory, and visual feedback.
Active treatment involves binocular (dichoptic) stimulation of peripheral retinal areas followed by gradual encroachment upon central areas.
Use dissimilar (1st degree) targets initially, then similar (2nd degree) targets.
Next, physiological diplopia training.
Stimulus parameters are brightness, contrast, color, size, on-period, position, and movement of targets.
Reinforce therapy with kinesthetic, auditory, and visual feedback.
Sensory fusion should be highly developed before motor fusion training begins.
For both, however, qualitative aspects are more important than quantitative aspects (viz., facility more important than magnitude).
Improve grades of fusion in order of difficulty.
Train both lower and upper stereo-thresholds.
Facility and accuracy of accommodation is very important in heterophoria.
Transference to free-space situations must be recognized.
When changing mechanical advantage of oculo-rotary muscles by surgery, post- surgical comitance is desired goal.
Smaller surgical changes on several muscles tend to give better comitance.
Second operation may be necessary to correct vertical deviations.
Pre- as well as post-surgical optical correction and orthoptics can be helpful.
Surgery may be required for large heterophorias (i.e., 15 p.d. vertical).