Presentation Aphakia ppt.pptxmmmmmmmmmmmmm

Aphekia

1. APHAKIA & PSEUDOPHAKIA Presented By, ABINGHOSH AB SACO INSTITUTE OF OPTOMETRY

2. Aphakia Aphakia literally means absence of crystalline lens from the eye. However, from the optical point of view, it may be considered a condition in which the lens is absent from the pupillary area and does not take part in refraction. Aphakia produces a high degree of hypermetropia .

3. Causes . 1. Congenital absence of lens . May occur is a very rare condition.
2. Surgical aphakia occurring after removal of lens is the commonest presentation.
3. Aphakia due to absorption of lens matter is noticed rarely after trauma in children.
4. Traumatic extr usion of lens from the eye also constitutes a rare cause of aphakia .
5. Posterior dislocation of lens in vitreous (traumatic or spontaneous) produces optical aphakia .

4. Traumatic extrusion posterior dislocation of lens

5. Optics of Aphakia Von Helmholtz first worked on the optics of aphakia . Then Benito Daza De Valdes suggested that aphakia could be corrected by spectacles . Optics of aphakia can be discussed under fol lowing heads: • Changes in cardinal data of the eye • Image formation in the aphakic eye • Visual acuity in aphakia • Accommodation in aphakia • Binocular vision and aphakia

6. Changes in cardinal data of the eye Following optical changes occur after removal of crystalline lens
1. The eye becomes highly hypermetropic .
2. Total power of the eye is reduced to about +44 D from +60 D.
3. The anterior focal point becomes 23.2 mm in front of the cornea.
4. The posterior focal point is about 31 mm behind the cornea, ie . About 7 mm behind the eyeball. 5. The two principal points are almost at the ante- rior surface of cornea.
6. Nodal points are very near to each other and are located about 7.75 mm behind the anterior surface of corneal

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