Aphakia

Aphakia is the absence of the crystalline lens from the eye.

• Causes: surgical removal (intracapsular or extracapsular cataract extraction without intraocular lens), traumatic loss or dislocation, congenital absence (primary aphakia, rare), lensectomy for lens subluxation, or an intraocular lens that was explanted.
• Optical effect: loss of about 17 to 20 dioptres of power (lens contributes about one third of the eye's refractive power), producing high hypermetropia of about +10 to +12 dioptres in an emmetropic eye, and loss of accommodation.
• Common in infants after congenital cataract surgery (infantile aphakia).

• Blurred distance and near vision unless corrected; a deep anterior chamber, iridodonesis (trembling iris), vitreous in the anterior chamber or pupil, shimmering vitreous.
• Spectacle correction (+10 to +12 dioptre lenses) causes: about 25 to 30 percent image magnification, ring scotoma in the periphery (jack-in-the-box phenomenon), pincushion distortion, spherical aberration, and aniseikonia and diplopia in unilateral aphakia (unable to fuse images that differ by over 5 percent).
• Complications: retinal detachment (higher in aphakia), glaucoma (open and closed angle, especially after congenital cataract surgery), cystoid macular oedema, vitreous prolapse, amblyopia in children, increased risk of corneal decompensation.

• Slit lamp examination (absence of lens, capsular remnants, iridodonesis, vitreous status), refraction with trial lenses, keratometry.
• Intraocular pressure, gonioscopy, dilated fundus examination, macular optical coherence tomography.
• Assess candidacy for secondary intraocular lens: corneal endothelial cell count, capsular support, iris status, angle.
• For infants: cycloplegic refraction and amblyopia assessment.

• Spectacles: suitable only for bilateral aphakia; thick, heavy lenses with limited field.
• Contact lenses: the preferred non-surgical correction, especially unilateral aphakia (magnification about 7 to 12 percent, tolerable binocular vision). Extended wear silicone elastomer lenses are used in infants (initial power about +25 to +30 dioptres), changed as the eye grows, with over spectacles for near.
• Secondary intraocular lens implantation (when anatomy allows):
  • Sulcus fixated posterior chamber lens if capsular support remains.
  • Scleral fixated lens (sutured with 9-0 or 10-0 polypropylene, glued intrascleral Hoffman pocket technique, or flanged 3-piece lens technique).
  • Iris claw (iris fixated) lens, or anterior chamber lens with open loop design when endothelium and angle are suitable.
• Infantile aphakia: contact lens or spectacles for the first years; intraocular lens placed after about 2 years of age or later when axial growth stabilises, with an intended initial undercorrection.
• Treat complications: glaucoma surveillance (pressure at every visit), prophylaxis for retinal detachment (examination and laser to peripheral lesions), cystoid macular oedema (topical nepafenac 0.1 percent three times daily and prednisolone acetate 1 percent four times daily).
• Amblyopia treatment in children (occlusion therapy).