Refraction in Aphakia

Fig:- Patient with Aphakic Glass

When the crystalline lens is removed and intraocular lens is not implanted, the patient needs a very strong plus correction. In such situation absence of accommodation and clear vision hinders fixation and therefore, retinoscopy is of little help. Multiple pinhole may be used to assess the potential of the eye. Keratometer and autorefractometer both may provide good starting point. 

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An aphakic eye and a normal eye do not work together as a team. First refraction after surgery is advisable after 6 weeks of surgery and final prescription is given after a recheck again at a week’s interval. Fogging method is of  no use. Refraction with the stenopaic slit is very quick method of refraction in such case. Most aphakes are against-the-rule astigmatism with the axis of plus cylinder lens around 180°. 

Fig:- Stenopaic Slit

Place 1mm wide slit in the trial frame and a high plus spherical lens. Rotate the slit until the position of best acuity is found. Compare the acuity with the slit position at opposite meridian. Once the two principal meridians are found out, correct the meridian with better acuity first with spherical lens and then the other with additional plus spherical lens. 

The first corrected meridian will give spherical correction and the second corrected meridian will give the summation of spherical and cylinder. The cylinder will be found by subtracting the first meridian correction from the second one. The first meridian will be taken as axis of the cylinder lens. Once the maximum acuity is achieved, remove the slit and replace the additional lens with plus cylinder, and verify.