Managing Corneal Dystrophies With Lenses
New designs and materials can aid practitioners in treating dystrophies and associated conditions.
By Long D. Tran, OD, FAAO
In general, corneal dystrophies can be diverse and difficult to diagnose. The subtle, and many times similar, corneal manifestations that these conditions present can often make it challenging to determine one from the other. A detailed patient history and a careful biomicroscopy examination are necessary. Even if you can make only a tentative diagnosis, you should initiate management of the patient's symptoms.
The array of symptoms that patients who have corneal dystrophic disease will experience can vary from none to severe. In the early stages of the disease, patients may complain only of blurry vision and/or a foreign body sensation. In the advanced stages of the disease, patients may have limited vision in conjunction with severe discomfort or pain.
Treating these corneal dystrophies, by and large, involves managing patients' symptoms during episodes of epithelial and stromal compromise. Poor epithelial adhesion due to a physiologic change of any of the underlying corneal layers (basement membrane, Bowman's layer, stroma, and endothelium) may result in epithelial defects and erosions. Patients who suffer from corneal erosions require prompt management of the pain and decreased vision. While therapeutic and surgical options are both viable, bandage soft contact lenses can serve as a useful and readily available alternative. In addition to reducing patient symptoms and promoting corneal healing, bandage contact lenses may also delay the need for more invasive treatment procedures such as corneal stromal puncture or phototherapeutic keratectomy.
Bandage Lens Selection
Contact lenses have long been used to treat and manage corneal diseases (Amos, 1975; Aquavella, 1976). After assessing a patient's condition and symptoms and concluding that the treatment plan calls for a bandage contact lens, it's time to select the appropriate lens. The success of a bandage lens can depend on the prescribed parameters. Lens material and design both play a significant role in the way the lens fits and interacts with the eye. To prescribe the most optimal bandage contact lens for each patient's condition, there are a few questions to consider.
What is the Goal of the Bandage Lens?
Protection Soft bandage lenses can be effective in corneal protection, corneal healing, and pain relief (Lim et al, 2001, Kanpolat and Ucakhan, 2003). Repeated cornea-lid interaction during blinking or eye movements can delay epithelial regeneration and healing. A bandage lens can serve as a protective shield to minimize this type of interaction. Bandage lenses can also assist with corneal healing by providing structural support to guide epithelial cell migration over the area of erosion or compromise.
Dehydration In corneal dystrophic conditions that can cause corneal edema, such as Fuchs' endothelial dystrophy, managing the edema takes priority. In this case, a high-water-content soft contact lens can reduce corneal hydration. Pervaporation from the outer contact lens surface can draw moisture from the corneal environment, thereby reducing corneal edema.
Vision The bilateral nature of corneal dystrophies may present as corneal defects or erosions in both eyes at the same time. While traditional management of severe corneal defects has involved therapeutic treatment and pressure patching, it is not practical to pressure patch both of the patient's eyes simultaneously. In this case, practitioners can prescribe bandage lenses with the patient's refractive correction to protect the corneas while allowing the patient to function visually.
What Type of Lens?
The high-Dk property of silicone hydrogel lenses makes them ideal bandage lenses for long-term use. The high-oxygen-transmissibility properties of these lenses help with corneal healing by allowing the cornea to be as close to a “no-lens” state as possible. The extended wear modality also helps minimize undue stress to the cornea from repeated daily lens application and removal. Silicone hydrogel lenses such as Acuvue Oasys (Vistakon), Air Optix Night & Day Aqua (Ciba Vision), and PureVision (Bausch + Lomb) have all received U.S. Food and Drug Administration (FDA) approval for therapeutic use as shown in Table 1.
While it seems most practical to utilize a silicone hydrogel lens for the added benefit of increased oxygen transmissibility, a traditional hydrogel lens may have some advantages over its counterpart. Bandage contact lens therapy is often prescribed to patients in conjunction with topical ocular pharmaceutical therapy. When compared to silicone hydrogel lenses, traditional hydrogel lenses, more specifically non-ionic lenses (FDA Group I & II), have been found to release more topical agents, such as ciprofloxacin, into the corneal environment (Karlgard et al, 2003). This suggests that in cases in which patients need to use topical agents while wearing a protective bandage lens and in which frequent lens removal for instilling these agents is not conducive to corneal healing, it may be more advantageous to prescribe a hydrogel lens to the patient rather than a silicone hydrogel. Keep in mind that this should be done cautiously and only for brief periods of time as the risk of hypoxia and infection is greater with the extended wear of a hydrogel lens than a silicone hydrogel lens.
Another advantage hydrogel lenses have over silicone hydrogel lenses, especially first-generation silicone hydrogel lenses, is that they generally have lower modulus values. This characteristic allows them to drape over the corneal surface more uniformly. Inadequate draping by higher-modulus lenses has been reported to occasionally induce an abrasive shear force on the epithelial surface of the cornea, resulting in corneal chafing (Holden et al, 2001).
Fitting Bandage Soft Lenses
Currently, there is little guidance in the literature on how to prescribe bandage contact lenses. This is likely due to the fact that each case is unique and may present with a different array of clinical signs and symptoms. As a result, it is difficult to recommend specific lenses for specific conditions. Following are some general considerations for fitting bandage contact lenses.
Base Curve Selection The fit of a bandage contact lens is the key to its success or failure. To protect the cornea and not induce any additional corneal injury, the bandage lens should not be fitted too loosely so as to allow for excessive movement. Excessive lens movement may disrupt newly regenerated epithelial cells and further delay healing. The lens also should not be fitted so tightly that it might prevent adequate tear exchange, resulting in keratopathy. The goal is to achieve approximately 0.5mm to 1.0mm of lens movement with each blink. Any clinical signs of conjunctival dragging or indentation might indicate that the lens is fitting too tightly. Unfortunately, many of today's soft lenses, especially silicone hydrogel lenses, are currently available in only one base curve.
Lens Coverage and Centration It is ideal for bandage soft lenses to center on the cornea and to provide limbal-to-limbal coverage; however, similar to base curves, practitioners are limited in their selection of overall lens diameters. Most spherical silicone hydrogel lenses have diameters between 14.0mm to 14.5mm.
Lens Power Selection Corneal dystrophies are bilateral in nature, but corneal signs such as erosions typically present in one eye at a time. If the patient's symptom is unilateral and he is able to attain acceptable vision from the contralateral eye, consider using a plano or low-power bandage lens to keep the lens profile thin. A thin-profile lens will help allow more oxygen transmission to the healing cornea. A thick lens may have increased eyelid interaction and result in more on-eye movement. This lens movement may disrupt the healing epithelium and cause the patient further pain or discomfort.
Tell patients when their bandage lens contains no corrective prescription. Patients may become alarmed if they associate their healing progress with how well they are able to see. They should also be cautioned to avoid activities such as driving for which binocular vision is essential.
Other Lens Considerations
Conventional GP contact lenses are seldom used as bandage lenses. Their relatively small size and movement on the eye do not make them ideal bandage lenses to be used for corneal healing and protection. Yet, in corneal conditions such as Meesmann's dystrophy and the more severe Stocker-Holt variant, in which the clinical findings include punctate type of epithelial defects as opposed to the ulcerative type observed in corneal erosions, a GP lens can be a better option for visual recovery (Figures 1 and 2).
Figure 1. Ulcerative cornea defect.
Figure 2. Superficial punctate epithelial defects.
Patients who have epithelial punctate opacities and epithelial vesicles typically experience glare, photophobia, and visual reduction (Weiss et al, 2008). These symptoms are magnified when the corneal findings are located centrally. A GP lens may be used in these cases to mask the irregularities of the corneal surface. The tear lens can “fill-in” the epithelial vesicles and provide patients with fewer symptoms and improved vision. If properly fitted, the GP lens will impose minimal risk to the healing cornea.
Fitting a GP lens on a compromised cornea is similar to that of fitting a normal cornea with the exception that you must take more care to ensure an overall clearance fit over the area of concern. Excessive bearing by the GP lens on the corneal surface may induce additional epithelial damage. This can be identified by sodium fluorescein uptake of the cornea in the area(s) of lens bearing or touch. Increasing the sagittal height of the lens helps alleviate this.
Minimize GP lens movement and increase stability by enlarging the overall diameter of the lens. This will also help the lens to vault over the areas of compromised cornea. Keep in mind that a GP lens will require movement for adequate tear exchange. Insufficient lens movement may result in lens adhesion and subsequent corneal punctate keratitis (Bennett et al, 2005).
It is also important for the GP lens to have an acceptable amount of peripheral corneal clearance. Minimal peripheral corneal clearance by the lens may result in lens binding, absence of lens movement, and poor tear exchange. The adverse effects of this are mentioned above. Conversely, excessive peripheral lens clearance may increase eyelid interaction and lens movement upon blink, possibly resulting in additional corneal insult.
A major benefit of using a GP lens rather than a soft lens is that you can dictate nearly every parameter of the lens including the size (overall diameter), power, peripheral clearance, and material. There is also a wide selection of GP materials that will provide high oxygen transmission to the cornea. Lastly, lens uptake of topical therapeutic agents is not a concern when wearing GP lenses as it is with soft hydrogel or silicone hydrogel lenses.
Scleral GP lenses can be effective in managing severe corneal conditions when other forms of therapy have failed (Rosenthal, 2000). When properly fitted, the “liquid bandage lens” created by the scleral lens can provide moisture and protection to the cornea while distributing its entire weight and bearing onto the sclera. Patients who are fitted with these lenses generally find excellent lens comfort and decreased dryness symptoms (Visser, 2007). While the fitting of these specialty lenses will not be discussed here, practitioners should consider scleral lenses as a viable option for patients who are unresponsive to other therapy.
Corneal dystrophies can manifest themselves as a wide array of corneal and ocular conditions (Table 2). Advancements in contact lens designs and materials have empowered practitioners with valuable tools to successfully treat and manage these corneal manifestations. When prescribed as bandage contact lenses, both soft and GP lens materials have the ability to play a vital role in corneal healing and visual recovery of these patients. CLS
The author would like to thank Drs. Charissa Lee and Timothy Edrington for their assistance with this article.
For references, please visit www.clspectrum.com/references.asp and click on document #184.
|Dr. Tran is an assistant professor at the Southern California College of Optometry. He is also the clinical director of Northpark Optometry, Inc. in Irvine, Calif. Contact him at email@example.com.|