Occasional Exotropia with Normal Correspondence
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.
Full minus Rx is advisable for exo-deviations.
What is the deviation at distance and near after neutralizing the refractive error? Added minus power at any distance for exo-deviations.
This reduces the deviation according to size of the AC/A and power of the added lens.
Look for rapid refusion or less frequent deviation.
Base-in prism more useful in exotropia than exophoria.
However, exo- deviations respond well to vision therapy in pre-presbyopes and vision therapy should be used prior to prism therapy.
Vertical prisms should be prescribed for the vertical deviation present with eyes in "ortho" position.
Rx vertical prism 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.
Effective for suppression and amblyopia.
USE PART TIME occlusion (2 to 4 hours per day) or over a portion of the lens (e.g.
upper part of the lens for distance occlusion), NOT FULL TIME occlusion.
Complete occlusion better than graded.
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 patients generally have very little amblyopia.
Treat most types of unsteady and/or eccentric fixation in conjunction with acuity improvement program.
Stimulate fovea under monocular and ESPECIALLY 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 and pathological diplopia training.
For occasional exotropes with NRC the goal is awareness of pathological diplopia when eye deviates.
Stimulus parameters are brightness, contrast, color, size, on-period, position, and movement of targets.
Reinforce therapy with kinesthetic, auditory, and visual feedback.
This portion of therapy should be initiated as soon as possible.
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 as binocularity develops in strabismus.
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 angles (i.e. more than 30 p.d. exo).