Aphakia
Dennis Burger
Larry J. Davis
▪ INTRODUCTION
While the number of patients undergoing cataract surgery continues to increase, the number who remain aphakic following surgery has been declining rapidly since the mid-1980s. The quality of intraocular lenses (IOLs), the improved surgical techniques, and the safety of intraocular lenses have combined to be a driving force in reducing the number of aphakic patients. Although IOLs have resulted in greatly reducing the number of new aphakic patients, they have not eliminated aphakia for all patients requiring removal of the crystalline lens. The use of intraocular lenses is considered risky for some patients following trauma and complicated intraocular surgery and for relatively young patients, especially infants.
Perhaps no single population has experienced the benefits of contact lenses more than those who are aphakic. The thick spectacle lenses necessary for the aphakic eye (usually +12.00 D to +16.00 D) induce a magnification of at least 30%.1 Restrictions of the peripheral visual field are also found while wearing spectacle lenses for the correction of aphakia. Prismatic effect is found to increase toward the edge of the lens, resulting in a ring scotoma. Although lenticular designs reduce the thickness and mass of these lenses, they may reduce the “optical” size of the lens, further restricting the visual field. Patients attempt to compensate for these effects by turning their head to scan the visual field. Contact lenses offer reduced magnification and better visual performance by eliminating visual field restrictions, and eliminate the use of the thick spectacle lenses, which are heavy, cosmetically unattractive, and optically inferior to contact lenses.2,3
▪ ADULT APHAKIC PATIENTS
Patient Selection
All contact lens wearers must perform routine lens care to maintain a lens with clear optical quality that is free from contamination. Once the decision is made to proceed with a contact lens correction, the patient, or in the case of extremely young or old patients, the guardian, should be advised of the required lens maintenance. Some factors to consider include specific visual requirements, best potential visual acuity, manual dexterity, willingness or ability to participate in lens care, and if indicated, social support system.
Ideally, the corneal astigmatism should be two diopters or less to maintain a well-fitting contact lens. In most cases (with the exception of infantile aphakia), this would mean fitting approximately 4 to 6 weeks following the primary surgical procedure. Against-the-rule corneal cylinder, which may occur from loose sutures or wound gape, can complicate the fitting of a contact lens. Therefore, while an attempt should be made to reduce the corneal cylinder as much as possible, having a moderate amount of with-the-rule cylinder is better than leaving the patient with even a small amount of against-the-rule corneal cylinder. Patients who have become aphakic as a result of blunt or penetrating trauma should be allowed sufficient time to reduce any intraocular inflammation. While a period of 4 to 6 weeks is also usually adequate in
this group of patients, some may require a longer amount of time. This is usually of no consequence if the patient is beyond the critical period and without risk of refractive amblyopia and if good visual acuity is maintained in the paired eye. Correction of the pediatric aphakic patient should be performed as soon as possible. Most often this can be achieved within 5 days following the primary surgical procedure. This is especially true if small-incision techniques are used, which allow for a short healing period and reduced postoperative astigmatism.
this group of patients, some may require a longer amount of time. This is usually of no consequence if the patient is beyond the critical period and without risk of refractive amblyopia and if good visual acuity is maintained in the paired eye. Correction of the pediatric aphakic patient should be performed as soon as possible. Most often this can be achieved within 5 days following the primary surgical procedure. This is especially true if small-incision techniques are used, which allow for a short healing period and reduced postoperative astigmatism.
Fitting Principles
Because of the large vertex powers and frequent unpredictability of lens dynamics while on the eye, diagnostic lens application is essential. During the prefitting evaluation, in addition to the usual evaluation of corneal curvature, refractive status, visual acuity, tear quality, and external disease, any results of undercorrecting the refractive cylinder should be evaluated. As the best corrected visual acuity in many of these patients is 20/40 or worse, residual cylinder may have no effect on their optimum visual acuity. Diagnostic fitting, using high-powered plus lenses, will improve the accuracy of the initial prescription by reducing any errors in compensating for vertex distance. It is also essential to evaluate lens movement and centration while performing a diagnostic fitting. When fitting gas permeable (GP) lenses, they will frequently be found to decenter and a careful fluorescein pattern evaluation is indicated. The use of a hydrogel lens requires careful evaluation of lens fit as well. Adequate lens movement is essential to reduce complications resulting from tight-fitting lenses.
Lens Materials
Gas Permeable Lenses
When to Use:
Once the decision is made to proceed with contact lenses, practitioners are presented with an initial decision of whether to use a soft or GP contact lens design. Patients having no contact lens experience are usually fit with a rigid lens. This is especially true if the corneal curvatures are 43.00 D or flatter, with 2.00 D or less with-the-rule corneal cylinder, and if the upper lid is positioned at or below the superior limbus. Any amount of against-the-rule astigmatism can negatively influence centration of a rigid lens design. GP contact lenses offer several distinct advantages over their hydrogel counterparts (Fig. 17.1). Often, those patients most likely to reject GP contact lens wear are those having previous experience wearing a hydrogel contact lens. If, after proceeding with the fitting and evaluation of GP lenses, it is determined that an adequate fitting relationship or comfort cannot be achieved, refitting with a hydrogel lens design is usually well accepted by the patient. Patients who have experienced serious adverse reactions (e.g., tight lens syndrome, keratitis, severe giant papillary conjunctivitis) while using a hydrogel contact lens are more likely to successfully adapt to GP lenses than those wearing hydrogel lenses without apparent adverse effects. These patients must possess the motivation to accept the change in lid sensation, movement, and handling required for a GP lens design.
Lens Designs:
Because of the high plus powers of aphakic lenses resulting in a large center thickness, those attempting to fit rigid lenses must be familiar with various design characteristics that may improve the fitting relationship and enhance patient comfort. In most cases, a minus lenticular type of design is indicated. This both reduces lens mass by decreasing center thickness and creates a more posteriorly positioned center of gravity, thus enhancing lens centration. Lenticulation also produces a thicker lens edge profile and creates greater lens-to-lid interaction. This enhances lens movement and improves centration of the optical zone diameter over the pupil. Because of intralaboratory variability in the manufacture of lenticular lens designs, it is advisable to specify a specific lenticular design for better consistency and performance. This is achieved, in part, by requesting a particular flange radius (lenticular curve)
and optic cap (front optical zone) to be used during lens manufacture (Fig. 17.2). While a flatter flange radius will usually assist in maintaining a superior lens-to-cornea fitting relationship, this may also result in increased lens awareness. An approximate, desired flange radius between 1.0 and 2.0 mm flatter than the base curve radius in millimeters is recommended.4 For example, if a lens is ordered with a 45.00 D (7.50 mm) base curve radius, one would expect to order a flange radius of 8.5 to 9.5 mm. With few exceptions, the optic cap should be equal to the back optic zone diameter. A recommended diagnostic fitting set for lenticular lenses is found in Table 17.1.5 Effective Power and Vertex Power optical considerations are provided in Appendix A and B respectively.
and optic cap (front optical zone) to be used during lens manufacture (Fig. 17.2). While a flatter flange radius will usually assist in maintaining a superior lens-to-cornea fitting relationship, this may also result in increased lens awareness. An approximate, desired flange radius between 1.0 and 2.0 mm flatter than the base curve radius in millimeters is recommended.4 For example, if a lens is ordered with a 45.00 D (7.50 mm) base curve radius, one would expect to order a flange radius of 8.5 to 9.5 mm. With few exceptions, the optic cap should be equal to the back optic zone diameter. A recommended diagnostic fitting set for lenticular lenses is found in Table 17.1.5 Effective Power and Vertex Power optical considerations are provided in Appendix A and B respectively.
 ▪ FIGURE 17.1 Factors influencing the initial lens of choice for contact lens correction of aphakia. |
 ▪ FIGURE 17.2 Design of a minus carrier aphakic contact lens. |
TABLE 17.1 SUGGESTED LENTICULAR APHAKIA TRIAL LENS SET (RECOMMENDED MATERIAL IS PMMA OR A LOW DK GAS PERMEABLE MATERIAL) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Occasionally, patients having corneas >45.00 D may be fitted using a small-diameter, single-cut lens design. These lenses will require fitting at least 1 D steeper than K to improve lens centration. A recommended diagnostic fitting set for single-cut aphakic lenses is provided in Table 17.2.5 Because of the large center thickness of these lenses, it is recommended to order aphakic designs in a lens material with medium to high oxygen permeability (Dk). These lenses demonstrate good stability even when materials having Dk values above 100 are used. Most lens designs are now available including spherical, front toric, bitoric, bifocal, and multifocal powers.
Hydrogel and Silicone Hydrogel Lenses
When to Use:
Hydrogel and silicone hydrogel contact lenses offer potential advantages over their GP counterparts. Perhaps the most important advantage is immediate patient comfort. Second, a well-fitting contact lens is almost always obtainable. Therefore, one indication for using a hydrogel aphakic contact lens is when an inadequate fit occurs while using a GP lens design. In cases of low refractive astigmatism, hydrogel contact lenses usually perform quite well. If residual astigmatism reduces visual acuity, the appropriate cylindrical error can be incorporated into spectacles and worn over the contact lens. Finally, the ability to inventory most lens parameters provides immediate correction in cases of high refractive error without interruption of lens wear in the event of lens loss or damage. Patients who have become aphakic
secondary to trauma may also have iris defects resulting in large or ectopic pupils. These patients may benefit from a dark-tinted, hydrogel contact lens creating an artificial pupil and iris, which attenuates bright light. Hydrogel lens designs are more suitable for this application, as they more readily accept tint and encompass more of the corneal surface while providing better centration with decreased movement.
secondary to trauma may also have iris defects resulting in large or ectopic pupils. These patients may benefit from a dark-tinted, hydrogel contact lens creating an artificial pupil and iris, which attenuates bright light. Hydrogel lens designs are more suitable for this application, as they more readily accept tint and encompass more of the corneal surface while providing better centration with decreased movement.
TABLE 17.2 SUGGESTED SINGLE-CUT APHAKIA TRIAL LENS SET | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Lens Designs:
Several hydrogel lens designs are available for aphakic contact lens fitting. As many aphakic patients are elderly and benefit from using an extended-wear contact lens material, various aphakic contact lenses have been designed for use on an extended-wear schedule. An attempt is made to increase oxygen transmission by reducing lens thickness using lenticulation, increasing the water content of the material, or both. It has been several years since any new hydrogel contact lens materials and/or designs have been investigated for use in aphakia on an extended-wear basis. Most recently, one silicone hydrogel lens (O2OPTIX, O2OPTIX Custom Ciba Vision) and numerous spherical, toric, and bifocal planned-replacement lenses in aphakic powers have been introduced. A list of these lens designs is provided in Table 17.3.6
Complications
The thick lens designs necessary for aphakia create a hypoxic environment for the cornea. It is thought that many contact lens-related complications such as corneal infiltrates, neovascularization, corneal edema, and the more serious complication of infectious corneal ulceration are caused in part by the relative hypoxia that occurs while wearing contact lenses. Contributing factors in the elderly population are reduced aqueous tear secretion, meibomian gland dysfunction, blepharitis, and possibly decreased activity of the immune system. Periodic evaluation of proper lens fit should be performed, at minimum, every 6 months. Occasionally, a hydrogel lens is found to fit tighter with age. Routine annual or semiannual lens replacement may be beneficial in reducing acute tight lens syndrome. It has been demonstrated that lens removal before sleep is an important factor reducing the frequency of serious lens-related complications. Therefore, it is advisable to discourage the use of extended wear for most aphakic patients.
Occasionally, patients are unable or reluctant to perform lens care. Many patients lack the necessary manual dexterity to insert and remove contact lenses. Others may have a psychological reluctance to be actively involved in the required lens manipulation and care. Routine removal and cleanings may then be performed by a friend or family member or as a last resort in the office.
TABLE 17.3 HYDROGEL AND SILICONE HYDROGEL PLANNED-REPLACEMENT LENSES IN APHAKIC POWERS | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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