Constant Exotropia with Anomalous 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.
Base-in prism should be used with caution in constant exotropia with anomalous correspondence because of the possibility of increasing the angle due to prism adaptation.
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.
To determine the amount, add minus until the eyes are straight, then do a cover test (during diagnosis only).
In paresis, Rx greater prism power before eye with paretic muscle.
Use constant occlusion until the patient is able to maintain binocularity, then reduce the time.
Effective for suppression and amblyopia.
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.
Treat most types of unsteady and/or eccentric fixation in conjunction 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.
Large (greater than 2 to 4 p.d.) and steady E.F. should ordinarily be treated first as oculomotor problem; stimulate foveal fixation (e.g., entoptic imagery and auditory feedback) combined with pursuit and saccadic training.
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.
DO NOT emphasize pathological diplopia training; this is inappropriate due to the ARC.
Stimulus parameters are brightness, contrast, color, size, on-period, position, and movement of targets.
Reinforce therapy with kinesthetic, auditory, and visual feedback.
For constant exotropia with anomalous correspondence train with fusional vergence therapy.
Use convergence initiation therapy initially.
Vergence training requires fairly good acuity (20/60 or better) and not much suppression.
Surgery is likely to be needed as part of the total program for large angle deviations.
The final portion of therapy after fusion has been established.
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 and as binocularity develops in strabismus.
Transference to free-space situations must be recognized.
What is the deviation at distance and near after neutralizing the refractive error? Added minus power at any distance for exo-deviations (may need strong powers, up to 4 or even 5 D, as a training lens) .
These reduce the deviation according to size of the AC/A and power of the added lens.
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. reater than 30 p.d. exo).