Anisometrpia

anisometropia by jeevana

1. ANISOMETROPIA BY JEEVANA

2. The name is from four Greek components : an means not iso means same metr means measure ops means eye anisometropia

3. The optical state with equal refraction is isometropia When the total refraction of two eyes is unequal it is called anisometropia Small degree of anisometropia is of no concern A difference of 1D in two eyes causes a 2% difference in size of two retinal images A difference of upto 5% in retinal images of two eyes is well tolerated

4. In other words , an anisometropia upto 2.5 is well tolerated and that between 2.5 and 4 can be tolerated depending on individual sensitivity However if it is more than 4D , it is not tolerated. Each eye can be nearsighted (myopia) farsighted ( hyperopia ) or a combination of both its called antimetropia A difference in power of 2D or more is the accepted threshold to label it as anisometropia

5. 6% subjects aged 6 to 18 have anisometropia In certain types of anisometropia , the visual cortex of brain will not use both eyes together (binocular vision) , and will instead suppress the central vision of one of the eyes. If this occurs often enough during first 10 years of life while the visual cortex isdeveloping , it can result in amblyopia ,a condition where even when correcting the refractive errror properly , the person is still not correctable to 20/20

6. ETIOLOGY : CONGENITAL AND DEVELOPMENTAL ANISOMETROPIA occurs due to differential growth of the two eyeballs (uneven growth in both eyes and inborn defects in the eye) ACQUIRED ANISOMETROPIA due to asymmetric age change uniocular aphakia ofter removal of cataractous lens or due to implantation of IOL of wrong power

7. CLINICAL TYPES : SIMPLE ANISOMETROPIA : one eye is normal ( emmetropic ) and the other eye myopic or hypermetropic . COMPOUND ANISOMETROPIA : both eyes are hypermetropic or both eyes are myopic , but one eye is having higher refractive error than the other MIXED ANISOMETROPIA : one eye is myopic and other eye is hypermetropic ( antimetropia )

8. SIMPLE ASTIGMATIC ANISOMETROPIA : one eye normal and the other has either simple myopic or hypermetropic astigmatism COMPOUND ASTIGMATIC ANISOMETROPIA: both eyes are astigmatic but of unequal degree

9. SYMPTOMS Eye strain Headaches Sensitivity to light Complexity in reading Nausea and fainting Sheer tiredness Depth perception impaired Diplopia Amblyopia strabismus

10. STATUS OF BINOCULAR VISION IN ANISOMETROPIA : BINOCULAR SINGLE VISION : present in small degree of anisometropia UNIOCULAR VISION : when refractive error in one eye is of high degree , that eye is suppressed and develops anisometropic amblyopia . ALTERNATE VISION : when one eye is hypermetropic (for distant vision) and other eye myopic (for near)

11. DIAGNOSIS If a person has anisometropia it is usually detected or diagnosed when the child has a vision examination If it happens in an older person they may notoice that their vision is blurry and go in for examination By the symptoms Usually it is made after retinoscopic or autorefractometry in patients with defective vision

12. TREATMENT: SPECTACLES : the corrective spectacles can be tolerated upto a maximum difference of 4D CONTACT LENSES for higher degrees of anisometropia ANISEIKONIC GLASSES available but results are disappointing

13. INTRAOCULAR LENS IMPLANTATION for uniocular aphakia REFRACTIVE CORNEAL SURGERY for unilateral high myopia , astigmatism , hypermetropia PHAKIC REFRACTIVE LENSES (PRL) AND REFRACTIVE LENS EXCHANGE (RLE) quite useful in very high degree anisometropia