Refractive disorders in ophthalmology.pptx
- 1. REFRACTIVE DISORDERS Mushabe Reagan
- 2. CONVEX/ +LENS Uses of convex lens. Correction of hypermetropia, aphakia and presbyopia. Features (i) The convex lens is thick in the centre and thin at the periphery (ii) An object held close to the lens, appears magnified. (iii) When a convex lens is moved, the object seen through it moves in the opposite direction to the lens.
- 4. CONCAVE LENS It is used for correction of myopia Features (i) It is thin at the centre and thick at the periphery. (ii) An object seen through it appears minified. (iii) When the lens is moved, the object seen through it moves in the same direction as the lens.
- 6. CYLINDRICAL LENS Prescribed to correct astigmatism Features (i) When the cylindrical lens is rotated around its optical axis, the object seen through it becomes distorted. (ii) The cylindrical lens acts in only one axis, so when it is moved up and down or sideways, the objects will move with the lens
- 7. AXES OF THE EYE Optical axis is the line passing through the centre of the cornea (P), centre of the lens (N) and meets the retina (R) on the nasal side of the fovea. Visual axis is the line joining the fixation point (O), nodal point (N), and the fovea (F). Fixation axis is the line joining the fixation point (O) and the centre of rotation (C).
- 10. HYPERMETROPIA/ HYPEROPIA Parallel rays of light coming from infinity are focused behind the retina with accommodation being at rest. The posterior focal point is behind the retina, which therefore receives a blurred image.
- 12. CAUSES Axial hypermetropia - axial shortening of eyeball. Curvatural hypermetropia - curvature of cornea, lens or both is flatter than the normal Index hypermetropia - decrease in refractive index of the lens in old age. Positional hypermetropia – posteriorly placed crystalline lens. Aphakia
- 13. TYPES Simple hyperopia Functional hyperopia Pathological eg; consecutive, aphakia, index and positional
- 14. SYMPTOMS Asymptomatic Asthenopia; tiredness of eyes, frontal or fronto-temporal headache, watering and mild photophobia Defective near visison Small eyeball Small cornea Shallow AC Optic disc changes
- 16. TREATMENT Prescription convex lens Can use ; 1. Spectacles are most comfortable, safe and easy method of correcting hypermetropia. 2. Contact lenses are indicated in unilateral hypermetropia (anisometropia).
- 19. MYOPIA/ SHORT SIGHTEDNESS Parallel rays of light coming from infinity are focused in front of the retina when accommodation is at rest
- 21. CAUSES Axial myopia - increase in anteroposterior length of the eyeball. Curvatural myopia - increased curvature of the cornea, lens or both. Positional myopia - anterior placement of crystalline lens in the eye. Index myopia - increase in the refractive index of crystalline lens Myopia due to excessive accommodation
- 22. TYPES Congenital myopia Simple myopia aka school myopia Pathological or degenerative myopia Acquired myopia which may be: (i) post-traumatic; (ii) post- keratitic; (iii) drug-induced, (iv) pseudomyopia; (v) space myopia; (vii) night myopia; and (viii) consecutive myopia.
- 23. PRESENTATION Defective vision – poor distance vision Night blindness Muscae volitantes Asthenopia Half eye shutting
- 24. EXAM FINDINGS Prominent eyeball Large cornea Deep AC Large and poorly reactive pupils Optic disc changes
- 25. COMPLICATIONS Retinal detachment Complicated cataract Vitreous haemorrhage Choroidal haemorrhage Strabismus
- 26. TREATMENT Prescription of concave lens Surgical management Genetic counselling Low vision aids
- 28. ASTIGMATISM Rays of light entering in the eye cannot converge to a point focus but form focal lines
- 30. CAUSES Corneal astigmatism – abnormal curvature of cornea. Lenticular astigmatism. It may be: i. Curvatural- curvature of lens ii. Positional - tilting or oblique placement of lens. iii. Index astigmatism Retinal astigmatism - oblique placement of macula
- 31. TYPES Simple myopic Simple hypermetropic Compound myopic Compound hypermetropic Mixed
- 32. PRESENTATION Defective vision Blurring of objects Abnormal shape of images Asthenopic symptoms Head tilt Half closed eyes
- 33. TREATMENT Prescription cylindrical lenses Surgical correction