Advanced Techniques
Aphakia

Patient Selection:
Certain guidelines apply for the selection of potential aphakic contact lens patients. They must be able to handle the lens either on a daily or a weekly basis and possess the ability to properly care for the lenses. Like any contact lens candidate there needs to be sufficient tear film as well as an absence of any serious corneal disease. In addition, there should be available to the patient some sort of assistance in times of distress.

Types of Rigid Aphakic Lenses:
:There are basically two types of rigid aphakic contact lenses. These include the minus carrier lenticular lens and the single-cut lens.

The conventional lenticular lens is rarely used since it tends to ride low when the upper lid collides with the steep curve of the anterior optic zone pushing it downward. This same occurrence can also cause lid irritation.

The minus carrier lens, on the other hand, is well supported by the upper lid and can be held in position about 1 mm above the corneal center. It is also much thinner than the conventional lenticular lens further reducing the tendency for it to drop over the limbus. The optic zone of the minus carrier lenticular lens generally is relatively small, about 7.0 mm in diameter. The smaller zone results in both reduced center thickness and lighter weight.

The single cut rigid aphakic contact lens is sometimes prescribed when one or more of the following conditions are met: small palpebral apertures, relatively steep corneas (over 45.00 D), or when other lens designs tend to ride low. Since these lenses are smaller than a lenticular design, the edges can be made thinner, making them more comfortable. Although smaller, the size of the optic zone of the single cut lens is quite comparable to that of the lenticular. One advantage to the single cut lens design is the absence of a sharp juncture between the two curves on the front surface thus eliminating the annoying lid bump. A disadvantage to the single cut lens is the difficulty encountered in removing this small steep lens from the cornea, especially for the elderly.

 

Aphakic Soft Lenses:

Aphakic contact lenses are the thickest lenses used. In the case of the high myope of say -12.00 D, the thinnest portion of the lens lies over the visual axis. A +12.00 D aphake, however, finds the thickest portion of the lens over the corneal cap and visual axis. Any corneal edema resulting from the use of soft lenses for aphakia, therefore, is found over the most critical part of that structure. Even when highly gas permeable lenses are used, the permeability at aphakic levels of lens thickness may still be relatively low. An aphakic soft lens can cause a 4% to 8% increase in corneal thickness.

Aphakic soft lenses can be expected to last from about six months to one year. Their life expectancy can be shortened by any of the following:

Aphakic Contact Lenses-General Difficulties

Any contact lens, rigid or soft, must be handled. This can be a problem for the elderly patient with arthritis, a head or finger tremor, or poor central visual acuity resulting from macular degeneration. Further, elderly patients often experience difficulty coping with lens insertions and maintaining adequate supplies of the necessary solutions. Those who live alone may fear one day being unable to remove their lenses. Bilateral aphakes can�t see to find their lenses unless they use a special accessory device.

For these and other reasons contact lenses for the correction of aphakia are being used with diminished frequency. Due to improved surgical techniques and materials, intraocular lens implants are becoming the treatment of choice for the great majority of cataract patients.