refractiveerrors aaaaasdcfrgbhhhhbgdfghg

Type of refractive errors

1. ERRORS OF REFRACTION

2. INTRODUCTION Refractive disorders are abnormalities of refraction that occur in the eye. Refraction results in the focusing of image on the retina of the eye, permitting vision. In refractive errors, vision is impaired because a shortened or elongated eyeball prevents light rays from focusing sharply on the retina. Blurred vision from refractive errors can be correctly with eyeglasses or contact lenses.

3. DEFINITION A refractive error is a very common eye disorder. It occurs when the eye cannot clearly focus the image from the outside world. The result of refractive error is blurred vision which is sometimes so severe that it causes visual impairment. Refractive error also known as refraction error is a problem with focusing light accurately on the retina due to the shape of eye.

4. EMMETROPIA Emmetropia ( optically normal eye) can be defined as a state of refraction, when the parallel rays of light coming from infinity are focusing at the sensitive layer of retina with the accommodation being at rest .

5. AMETROPIA Ametropia ( a condition of refractive error), is defined as a state of refraction, when the parallel rays of light coming from infinity, (with accommodation at rest), are focussed either in front or behind the sensitive layer of retina.

6. TYPES OF REFRACTIVE ERROR The types of refractive errors are: Myopia Hyperopia Astigmatism

7. MYOPIA It is near sightedness also known as short sightedness. It is a type of refractive error in which parallel rays of light coming from infinity are focussed in front of the retina when accommodation is at rest. Myopia is a condition of the eye where light focuses in front of the retina instead of on the retina this causes distant objects to be blurred while close objects appear normal.

8. Normal vision Myopia

9. ETIOLOGY OF MYOPIA Axial myopia results from increase in the antero- posterior length of the eyeball. Curvatural myopia occurs due to increased curvature of the cornea, lens or both. Index myopia results from increase in the refractive index of the crystalline lens associated with nuclear sclerosis.

10. PATHOPHYSIOLOGY Due to etiology factor degenerative changes causes by gradual loss of elasticity of lens Which leads to decreased ability to accommodate Then lead to refractive error

11. TYPES OF MYOPIA Congenital Myopia Degenerative Myopia Simple Myopia

12. CONGENITAL MYOPIA Congenital myopia is present since birth. Usually the error is of about -8 to -10 diopters, which mostly remains constant . It may be associated with other ocular congenital anomalies. Ex: cataract, megalocornea, aniridia and microphthalmos.

13. SIMPLE MYOPIA It is the commonest variety, which results from normal is starts biological variation in the development of eye. Simple myopia starts at school age and very slowly progresses till adult age. Usually the error does not exceed -6 to -8 diopters.

14. DEGENERATIVE MYOPIA Pathological myopia or degenerative myopia is a rapidly progressive error resulting in high myopia of -20 D or more. It is strongly linked with heredity.

15. CLINICAL MANIFESTATION There is reduced visual acuity for the distance of but near objects are seen clearly. Usually there is no headache. In pathological myopia, the patient may complain of seeing black spots floating in front of the eye, due to vitreous opacities. Ophthalmoscopically, the typical changes seen in the high myopia are: myopic crescent either on the temporal side of the optic disc or surrounding the disc and chorio-retinal myopic degeneration or atrophy at the periphery. In vary high myopia the eye are prominent (pseudoproptosis), the pupils are large and vision may be very poor even with optical correction.

16. MANAGEMENT Concave lenses in the form of glasses or contact lenses.

17. SURGICAL MANAGEMENT Radial keratotomy: Multiple radial incisions are given in the periphery of cornea in order to flatten the curvature of cornea.

18. Lasik laser: Laser assisted in situ the preferred surgical technique for correcting myopia of up to -12 D. The midstromal tissue is ablated with excimer laser after raising a 130-160 micron thick flap of anterior corneal tissue. Removal of clear crystalline lens: Removal of lens extra capsular cataract extraction (phacoemulsification) with IOL implantation of appropriate power is being recommended.

19. HYPEROPIA Hypermetropia (hyperopia) or long sightedness is the refractive state of the eye where in parallel rays of light coming from infinity are focussed behind the retina with accommodation being at rest. Thus the posterior focal point is behind the retina, which therefore receives a blurred image.

20. ETIOLOGY Axial hyoermretropia is by far the commenest form. It occurs due to short axial length of the eyeball. Curvatural hypermetropia occurs due to comparatively flatter curvature of the cornea or lens or both. Index hypermetropia results due to change in the refractive index of the lens. Absence of the lens (aphakia) either congenital or acquired (following surgical removal of the lens) leads to high hypermetropia.

21. CLINICAL FEATURES Tiredness of eyes Frontal or frontotemporal headache Watering Mild photophobia

22. MANAGEMENT Appropriate convex lenses in the form of spectacles or contact lenses.

23. SURGICAL MANAGEMENT Refractive corneal surgery

24. ASTIGMATISM Astigmatism is a type of refractive error where in the refraction varies in the different meridia of the eye consequently, the ray of light entering in the eye cannot converge to a point focus but form focal lines.

25. ETIOLOGY Usually occurs due to unequal curvature of cornea. Rarely it may occur due to subluxation abnormalities of the curvature of the lens.

26. SIGN AND SYMPTOMS Blurred vision Eye strain and eye fatigue Headache Dizziness Vomiting

27. TYPES OF ASTIGMATISM REGULAR ASTIGMATISM IRREGULAR ASTIGMATISM

28. MANAGEMENT Cylindrical lenses in the form of spectacles or contact lenses.

29. PRESBYOPIA Presbyopia (eyesight of old age ) is not an error of refraction, but a condition of physiological insufficiency of accommodation, leading to failing vision for near. It is usually occurs after 40 years of age.

30. ETIOLOGY Decrease in the accommodation power of crystalline lens with increasing age, leading to presbyopia occur due to: Decrease in the elasticity and plasticity of the crystalline lenses. Age related decrease in the power of ciliary muscle. Causes of premature presbyopia :- Hypermetropia Primary open- angle glaucoma Premature sclerosis of the lens Excessive close work

31. SIGN AND SYMPTOMS A tendency to hold reading material farther away to make the letter clearer. Blurred vision at normal reading distance. Eye strain or headache after reading or doing close up work .

32. MANAGEMENT Convex glasses of an appropriate power : At the age of 40 years – reading correction is + 1D. At the age of 45 years - reading correction is +1.5D. At the age of 50 years - reading correction is +2D. At the age of 55 years - reading correction is +2.5 D.

33. DIAGNOSTIC EVALUTION History collection Physical examination Snellens chart ophthalmoscopy

34. retinoscopy autorefractometry

35. SUMMERY Refractive error are disorders, not disease. A refractive error means that the shape of eye doesn’t bend light correctly, resulting in a blurred image. Types of refractive error are: Myopia : near sightedness Hyperopia :far sightedness Astigmatism :Irregularly shaped cornea, causing blurred vision.