Aphakia
 

An aphakic eye with broad iridectomy and peripheral iridectomy.  An aphakic eye with corneal oedema as a result of vitreous touch.

The patient has a cataract extraction without lens implant (examine the wound to see if this is done through phacoemulsification or otherwise). The patient may be wearing thick lenses or contact lenses. In intracapsular cataract extraction, there is usually iridectomy and the presence of vitreous  in the anterior chamber (examine the cornea for any decompensation due to vitreous touch).  Some patients may have extracapsular cataract extraction without implant (for example in clear  lens extraction for high myopia). In such cases, the absence of implant may be missed with a casual examination.  Others: In young children with aphakia, consider: lens dislocation such as Marfan's syndrome cataract extraction in juvenile chronic arthritis, look for cells and flare in the  anterior chamber and band keratopathy. During the examination, you may be asked to perform a direct ophthalmoscopy on a  high myopic patient with aphakia. The clue to the presence of aphakia is the relatively  low minus (concave) power on the ophthalmoscope needed to visualize the fundus.

Questions:

1. What is the average refractive power of the lens?

Answer
15 D

2. Assuming the radius of curvature of the cornea is 8mm and refractive indices are 1 (air) and 1.33 (cornea, aqueous and vitreous). What degree of axial myopia can be fully corrected by clear lens extraction?

Answer
An aphakic eye has an anterior focal distance of 23 and the posterior focal distance of 31 mm. A phakic eye which is myopic with an axial length of 31mm is equal to -21D. Therefore, clear lens extraction canfully correct a myopic eye measuring -21D.

3. What are the disadvantages of wearing aphakic spectacles?

Answer
Image magnification of about 30%
Spherical aberration giving a pin cushion effect
A 'jack-in-the-box' ring scotoma from the prismatic effect
Reduced visual field
Physical inconvenience due to the weight of the glasses
Cosmetic appearance, the eye appears unusually large

 

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