BINOCULAR VISION PowerPoint presentation.pptx

Binocular vision

1. A SEMINAR PRESENTATION ON BINOCULAR SINGLE VISION BY EZEYIM MAUREEN (O.D)

2. TABLE OF CONTENT INTRODUCTION DEVELOPMENT OF BINOCULAR SINGLE VISION GRADES OF BINOCULAR SINGLE VISION ANOMALIES OF BINOCULAR SINGLE VISION

3. INTRODUCTION When a normal individual fixes his visual attention on an object of regard, the image is formed on the fovea of both the eyes separately; but the individual perceives a single image. This state is called binocular single vision. In other words, binocular single vision is the coordinated use of both eyes so as to produce a single mental impression.

4. DEVELOPMENT OF BINOCULAR SINGLE VISION Binocular single vision is a conditioned reflex which is not present at birth but is acquired during first 6 months and is completed during first few years.The process of its development is complex and partially understood. Important milestones in the visual development are: • At birth there is no central fixation and the eyes move randomly. • By the first month of life fixation reflex starts developing and becomes established by 6 months. • By 6 months, the macular stereopsis and accommodation reflex is fully developed. • By 6 years of age full visual acuity (6/6) is attained and binocular single vision is well developed.

5. GRADES OF BINOCULAR SINGLE VISION Worth has described three grades of binocular single vision, which are best tested with the help of a synoptophore. Grade I—Simultaneous perception. It is the power to see two dissimilar objects simultaneously. It is tested by projecting two dissimilar objects (which can be joined or superimposed to form a complete picture) in front of the two eyes. For example, when a picture of a bird is projected onto the right eye and that of a cage on to the left eye, an individual with presence of simultaneous perception will see the bird in the cage (FigA).

6. FIG A

7. Grade II—Fusion. It consists of the power to superimpose two incomplete but similar images to form one complete image . FIG B

8. Grade III—Stereopsis. It consists of the ability to perceive the third dimension (depth perception). It can be tested with stereopsis slides in synoptophore . FIG C

9. ANOMALIES OF BINOCULAR VISION Suppression It is a temporary active cortical inhibition of the image of an object formed on the retina of the squinting eye. This phenomenon occurs only during binocular vision (with both eyes open). However, when the fixating eye is covered, the squinting eye fixes (i.e., suppression disappears). Tests to detect suppression include synoptophore tests and Worth’s 4-dot test.

10. Amblyopia Amblyopia a refers to a partial reversible loss of vision in one or both eyes, for which no cause can be found by physical examination of the eye, i.e., there is absence of any organic disease of ocular media, retina and visual pathway. Depending upon the cause, amblyopia is of following types which include strabismic amblyopia, stimulus deprivation amblyopia, anisometropic amblyopia, isometropic amblyopia, meridional amblyopia.

11. Clinical characteristics of an amblyopic eye are: 1.Visual acuity is reduced. 2.Crowding phenomenon 3.Fixation pattern may be central or eccentric. 4. Colour vision is usually normal, may be affected in deep amblyopia with vision below 6/36.

12. Treatment of amblyopia should be started as early as possible (younger the child, better the prognosis). Amblyopia therapy works best when initiated in young children under 3 years of age and these therapies includes Occlusion therapy i.e. occlusion of the normal eye to force the amblyopic eye to see is the main stay in the treatment of amblyopia. penalization; blurring of vision of normal eye either by using atropine (atropine penalization) or by using over plus lenses in spectacles (optical penalization) can be used as alternative when occlusion is not possible. Pleoptic exercise.

13. Abnormal retinal correspondence (ARC) In a state of normal binocular single vision, there is an existing precise physiological relationship between the corresponding points of the two retinae. Thus, the foveae of two eyes act as corresponding points and have the same visual direction. This adjustment is called normal retinal correspondence (NRC). When squint develops, patient may experience either diplopia or confusion. To avoid these, sometimes (especially in children with small degree of esotropia), there occurs an active cortical adjustment in the directional values of the two retinae. In this state fovea of the normal eye and an extrafoveal point on the retina of the squinting eye acquire a common visual direction i.e., become corresponding points. This condition is called abnormal retinal correspondence (ARC) and the child gets a crude type of binocular single vision.

14. Diplopia Diplopia refers to simultaneous perception of two images of a single object. Diplopia may be binocular or uniocular. Binocular diplopia occurs due to formation of image on dissimilar points of the two retinae. Causes of binocular diplopia are: ■Paralysis or paresis of the extraocular muscles (commonest cause)

15. ■Displacement of one eyeball as occurs in space occupying lesion in the orbit, and fractures of the orbital wall, ■Mechanical restriction of ocular movements as caused by thick pterygium and symblepharon. ■Anisometropia i.e., disparity of image size between two eyes as occurs in acquired high anisometropia , uniocular aphakia with spectacle correction).

16. TYPES OF BINOCULAR DIPLOPIA ■Uncrossed diplopia. In uncrossed (harmonious) diplopia the false image is on the same side as deviation. It occurs in convergent squint as in lateral rectus paralysis. ■Crossed diplopia. In crossed (unharmonious) diplopia the false image is seen on the opposite side. It occurs in divergent squint as in medial rectus paralysis.

17. REFERENCE Aslin, R.N. (1977) Development of binocular fixation in human infants. Joumal of Experimental Child Psychology, 23, 133-150. Aslin, R.N. and Jackson, R.W. (1979) Accommodative convergence in young infants: development of a synergistic sensory-motor system. Canadian Journal of Psychology, 33, 222-231. Atkinson, J. (1984) Human visual development over the first six months of life: a review and a hypothesis. Human Neurobiology, 3, 61-74. Baitch, L.W. and Levi, D.M. (1988) Evidence for non linear binocularinteractions in human visual cortex. Vision Research, 28, 1139-1143. Bagolini, B. (1967) Anomalous correspondence: definition and diagnostic methods. Documenta Ophthalmologica, 23, 346-398. Baker, D.H. and Meese, TS. (2007) Binocular contrast interactions: Dichoptic masking is not a single process. Vision Research, 47, 3096-3107. Baker, D.H., Meese T.S., Mansouri, B. and Hess, R.E. (2007) Binocular summation of contrast remains intact in strabismic amblyopia. Investigative Ophthalmology and Visual Science, 48, 5332-5338.