Strabismic ambylopia

Strabismus is a condition in which the eyes do not properly align with each other when looking at an object. The eye which is focused on an object can alternate. The condition may be present occasionally or constantly.If present during a large part of childhood, it may result in amblyopia or loss of depth perception. If onset is during adulthood, it is more likely to result in double vision.
Amblyopia is characterized by several functional abnormalities in spatial vision, including reductions in visual acuity, contrast sensitivity function, and vernier acuity, as well as spatial distortion, abnormal spatial interactions, and impaired contour detection. In addition, individuals with amblyopia suffer from binocular abnormalities such as impaired stereoacuity (stereoscopic acuity) and abnormal binocular summation
Those with strabismic amblyopia tend to show ocular motion deficits when reading, even when they use the nonamblyopic eye. In particular, they tend to make more saccades per line than persons with normal stereo vision, and to have a reduced reading speed.

1. UNIVERSITY OF GONDAR COLLEGE OF MEDICINE AND HEALTH SCINCES DEPARTMENT OF OPTOMETRY BINOCULAR VISION Strabismic ambylopia By Group 3 December 4 /2017

2. Outline definition of ambylopia, strabismic ambylopia causes of strabismic ambylopia diagnosis methods treatment

3. Sensory adaptations sensory adaptation s are the mechanisms by which any abnormality to binocular vision is componsated . Can be classified as binocular and monocular binocular ,1ARC 2 Suppression Monocular sensory adaptations are :- a, strabismic ambylopia and b, eccentric fixation.

4. Definition The definition of amblyopia(lazy eyes) is ‘reduced visual acuity not correctable by refractive means and not attributable to obvious structural or pathological ocular anomalies. Functional reduction in VA of an eye caused by disuse during the critical period of visual development. A visual loss resulting from an impediment or disturbance to the normal development of vision. The anatomy of the eye is intact or normal but it is lazy causing dullness of vision(reduction in visual acuity).

5. Functional ambylopia Catagory of ambylopia where no organic lesion exists: on eye exam a deficiency of form vision affecting either one or both eyes Strabismic amblyopia Deprivation amblyopia: Occlusion amblyopia Anisometropic amblyopia Isoametropic amblyopia 6) Psychogenic amblyopia

6. strabismic amblyopia Patients with strabismus who strongly favor one eye for fixation and who have a unilateral rather than an alternating fixation pattern are most likely to acquire strabismic amblyopia. occurring generally before the age of seven years , which cannot be corrected purely by accurate refraction. It should not be associated with any recognizable pathological cause, but should be attributable to an amblyogenic factor. Strabismic amblyopia represents a loss of the physiologic superiority of the fovea. This superiority is characteristic of the photopic state. The amblyopic eye is functionally at its worst at photopic luminance levels, at which point the foveae of these eyes display certain characteristics of the dark-adapted state.

7. Cause of strabismic ambylopia As the name indicates the main cause of this ambylopia is strabismus. especially esotropic pxs are likely to dev’p strabismic ambylopia, Patients with exotropia frequently are able to alternate fixation, which greatly minimizes their risk of developing amblyopia. In esotropia the fovea of the deviating eye has to compete with the strong temporal hemifield of the fellow eye. In exotropia the fovea competes with the weaker contra lateral nasal hemifield. Strabismic amblyopia is always unilateral and is caused by active inhibition within the retinocortical pathways of visual input originating in the fovea of the deviating eye. This inhibition is the consequence rather than the cause of strabismus and is elicited by overlap of the different foveal images transmitted to the visual centers from the retinas of the fixating eye and the deviating eye.

8. continued The etiology of strabismic amblyopia is similar to that of suppression. However, whereas suppression is restricted to binocular vision, and the visual acuity of each eye, when measured monocularly, is normal, amblyopia exists under binocular and monocular conditions. Thus amblyopia may be considered a carryover of suppression into monocular .However, amblyopia may also occur occasionally in strabismus without suppression of the fovea of the deviated eye. Thus, suppression alone cannot always be the cause of amblyopia.

9. Cont… Surgery :-In patients with infantile esotropia and no amblyopia, surgical correction increases the risk of developing amblyopia. Amblyopia will develop if the child has a preference for one eye.dis use may develop ambylopia to the eye .

10. Pathophysiology/clinical features Mechanism originates in visual cortex. Decrease in number of binocularly driven cells in striate cortex. Reduction in cortical blood flow and glucose metabolism Causes reduction in V.A, binocularity, dark adaptations, V.F defects, contrast sensitivity, spatial localisation, fixation, ocular motility, accommodation, crowding, attention, motion perception and temporal processing. Therefore fusion and streopsis that depend on clear image from each eye simultaneously are affected .

11. Visual Acuity Any difference in acuity between the two eyes represents an amblyopia of the eye with the poorer vision. Strabismic amblyopia has been found to be caused by active inhibition within the retinocortical pathways of visual input originating in the fovea of the deviating eye. This inhibition is elicited by overlap of the different foveal images transmitted to the visual centers . There will be low speed of reading small font sizes, more saccadic mov’t and ocular motion reduction.

12. Diagnosis From a practical clinical standpoint, a difference of two lines on a visual acuity chart is commonly used as a diagnostic criterion for amblyopia. any and every difference in visual acuity produced by amblyopiogenic factors should be classified as an amblyopia. Low visual acuity in one or both eyes out of proportion to the structural abnormality of the eye and excluding other visual disorders as causes for lowered VA. it can be defined as an intra ocular difference of two lines or more in acuity.

13. Cont... Random dot stereo test:- Strabismic amblyopia may be detected by tests assessing random dot Stereopsis. Which consists of a random dot stereogram upon which a series of parallel strips of cylindrical lenses are imprinted in certain shapes, which separate the views seen by each eye in these areas without stereopsis ,the image looks like a field of random dots but the shapes become discernible with increasing stereopsis. The image should be at 40 cm and exactly in the frontoparallel plane.

14. CROWDING PHENOMENON In patients with amblyopia, it is always importance to compare the vision obtained with visual acuity symbols presented in a row, to that obtained with isolated symbols on a uniform background. Many patients with amblyopia are capable of discriminating rather small visual acuity symbols when they are presented singly against a uniform background, whereas when presented in a row , as on a visual acuity chart, the symbols must be larger, often considerably larger, for a patient to be able to recognize them with the amblyopic eye.

15. Treatment methods Strabismic ambylopia should be detected as early as possible to treat it successfully. especially if detected before the age of 5 the underlined cause is corrected with glasses or surgery. There are different treatment methods including vision therapy orthopic exercises surgery

16. vision therapy A type of physical therapy for the eyes and brain ,highly effective ,non surgical treatment. it involves :- progressive program of vision exercises or procedures . Twice a week for 30 minutes. supervision by professional Therapeutics lenses Prisms Optical filters using an occuludor or eye patch

17. Cont... The normal eye is covered by occuludor or get pharmacological penalization by atropine drops to temporarily paralyze accommodation reflex ,this blurs he vision of the normal eye repetitive action of this tends the amblyopic eye to improve it’s VA. N.B don’t continue to practice this if not it bring some improvement until 6 months ,b/s “reverse ambylopia” may develop.

18. when and how to treat strabismic ambylopia? Research has shown that early surgical alignment is associated with better stereopsis in those patients with infantile esotropia treated in the first 24 months of life, because early surgery minimizes the duration of misalignment. However, in patients in which the strabismus is accompanied by amblyopia preoperatively, caregivers must decide whether to treat the strabismus or amblyopia first. Treating the strabismus first will decrease the length of misalignment and possibly increase the chance of some degree of binocularity. Treating the amblyopia first will potentially give the patient better vision in each eye, which may aid the stability of the postsurgical alignment.

19. If you got us What is ambylopia and what about strabismic ambylopia? List some causes of strabismic ambylopia ? How can you diagnose this ambylopia ? list at least two treatment methods for strabismic ambylopia ?

20. for further understanding References von Noorden GK. Binocular Vision and Ocular Motility: Theory and Management of Strabismus… Hoyt CS: Amblyopia: Aneuro-ophthalmic view. J Neuroophthalmol2005; 25: 227–231. 3 American orthopic journal volume 57,2007

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