Aphakia

Copy of PowerPoint presentation of Undergraduate (MBBS-prefinal year) lecture

taken for Gandhi Medical Students in January 2007)

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Aphakia

• When the crystalline lens has been removed condition is called aphakia. This this condition the crystalline lens is absent from its normal position.

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Causes of Aphakia

1. Congenital: a. True absence of lens, is a rare congenital condition, or b. Posterior dislocation of lens (lens is completely out of pupillary area, in posterior segment).

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Causes of Aphakia

2. Acquired:

a. Surgical removal of lens

b. Complete absorption of lens in children following trauma (act like surgical procedure, needling)

c. Posterior dislocation of lens (usually traumatic)

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Symptoms of Aphakia

Marked diminution of vision (in previously emmetropic individuals)

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Signs of Aphakia

1. Markedly reduced visual acuity

2. Conjunctival scar may or may not be there.

3. Corneo-scleral / corneal scar

4. Deep anterior chamber

5. Tremulousness of iris

6. Jet black pupil

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Signs of Aphakia

7. Absence of lens

8. High hypermetropic fundus

9. High hypermetropic refraction

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Optics in Aphakia

Eye becomes high hypermetropic due to removal of lens. There is only one converging structure i.e. Cornea, which separates two media of different refractive indices, air and aqueous plus vitreous.

Anterior focal distance becomes 23 mm (from 15 mm) and posterior 31 mm (from 24 mm)

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Optics in Aphakia

If the aphakic eye is 31 mm long (equivalent to -21 D axial myopia) the parallel light rays falling on cornea will focus on retina.

There is total loss of accommodation in aphakic eye.

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Optics in Aphakia

• Astigmatism, against the rule in phaco incision in upper sector , which is minimum. With the rule astigmatism in conventional ECCE with sutures in place in upper part and this astigmatism decreases after removal of sutures.

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Treatment

• Spectacle

• Contact Lens

• Intra-ocular implantation

a. Posterior Chamber

b. Iris claw lens

c. Anterior Chamber IOL

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Treatment

• Spectacle :

Indications: Bilateral Aphakia, High myopic patients (calculated IOL power less than 8 D) under going cataract surgery, and when patient refuses IOL implantation surgery.

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Treatment

• Spectacle: Patient who was emmetropic prior to lens removal operation usually requires For Distance: +10 D Sph and Astigmatic correction (usually +1 to +2 D Cyl at 180 deg in case of against the rule astigmatism, wherein vertical curvature of cornea is flatter than horizontal, and at 90 deg in case of with the rule astigmatism)

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Treatment

Spectacle Correction:

For Near: Addition of +3 D Sph to distance spherical correction.

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Disadvantages of Aphakic Spectacle

Disadvantages of aphakic spectacle: 1. Magnification of image (seen by patient) by 30% 2. Lack of eye-hand coordination 3. Reduced visual field and poor peripheral / eccentric acuity4. Ring scotoma from prismatic effect of the edge of the convex lens. Jack in the box phenomenon

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Disadvantages of Aphakic Spectacle

5. Physical discomfort of wearing heavy spectacle and cosmetically intolerable thick spectacle

6. Wearing different optical correction for different distances

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Contact Lens correction

Indications for use of Contact lens in aphakic patients:Young children, where IOL implantation is not considered safe (usually below the age of 2 years) Other aphakic patients where IOL has not been implanted, and cornea is suitable for contact lens fitting.

With contact lens magnification is around 8% which is tolerable, without causing binocular diplopia even in uniocular aphakics.

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Disadvantages of Contact Lens

1. Fitting and removal of contact lens is cumbersome procedure for most of our patients

2. Contact lens requires proper hygiene and cleaning of contact lenses

3. It may be difficult for elderly patients with tremors to manipulate contact lenses

4. Additional near (and sometimes intermediate distance) correction is required

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Intra-ocular lens (IOL) implantation

Best tolerated, there are no optical aberrations , magnification is negligible (usually 1-2%), IOL can be implanted in almost all cases undergoing cataract surgery

Additional near (and sometimes intermediate distance) correction is required (except in those patients where multi-focal IOL is implanted)

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Intra Ocular Lens Implantation

1. Done at the time of Cataract Surgery2. Secondary IOL (IOL implantation done in

an aphakic eye). This may be posterior chamber IOL implantation, in case where posterior capsule is present. Iris claw or anterior chamber IOL. Posterior chamber IOL implantation is preferred over other two types as there is minimum risk of complications.

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Posterior Chamber IOL Implantation

• In the bag posterior chamber IOL

or

• Sulcus fixated posterior chamber IOL

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Posterior Chamber IOL – In the bag

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Posterior Chamber IOL – Sulcus Fixated

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Iris Claw IOL

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Anterior Chamber IOL

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Anterior chamber IOL

Complications:

• There is higher risk of corneal endothelial decompensation leading to corneal edema.

• Uveitis Haemorrhage and Glaucoma (UGH) syndrome.