Why is contact lens correction preferred over spectacles in unilateral aphakia?

• A Contact lenses reduce spectacle-induced image magnification, minimising aniseikonia ✓
• B Contact lenses provide greater magnification, improving visual acuity
• C Contact lenses eliminate the need for accommodation
• D Contact lenses correct the irregular astigmatism of aphakia

Explanation

B high-plus spectacle lens in unilateral aphakia magnifies the retinal image by about 25 to 30 percent, producing disabling aniseikonia against the phakic fellow eye. Because a contact lens sits at the corneal plane, its magnifying effect is much smaller, around 7 percent, keeping the interocular difference within tolerable limits. Contact lenses do not increase magnification, they do not restore accommodation, and aphakia itself is not an irregular astigmatism.

Reference: Parsons' Diseases of the Eye, 23rd ed.

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Written and medically reviewed by the StethoPrep medical team.