Corneal Clarity

Starting at the Surface

By Thomas John, MD

Because refraction, and thus vision, begins at the plane of the cornea, this structure is the first and perhaps most essential component of good vision. All that follows—media clarity, macular function, optic nerve visual processing—cannot proceed without a healthy cornea. This new column will discuss the multi-pronged approach that ophthalmologists must use to achieve the corneal clarity that underlies good health and high quality of vision.

First Things First

To begin with, we must address the eyelids and the tear film, which have a direct impact on vision. Blepharitis, especially posterior blepharitis, can result in secondary evaporative dry eye and compromise vision. Even if an ophthalmic surgery is flawless, without due consideration of an optimal ocular surface the result is ultimately going to be sub-optimal—and likely result in an unhappy patient.

Hence, a well-functioning ocular surface is the common denominator to achieving the best visual outcomes of our patients. After we accomplish this, we can move on to any other necessary remedies.

First, treat blepharitis, dry eye and any lid abnormalities such as entropion, ectropion and trichiasis, and attend to surface growths such as pterygium or tumors. Other complicating states include chemical injuries, ocular cicatricial pemphigoid, Stevens-Johnson syndrome, diabetic keratopathy, regional neurogenic compromise and less common conditions such as aniridia and Riley-Day syndrome (dysautonomia). Some tear substitutes that closely mimic the normal tear constituents increase the nourishment of corneal epithelial cells and can further enhance the ocular surface in a positive direction and improve vision.

Surgical Advances

For patients best served by surgical intervention, the procedure cannot take place until the ocular surface is normalized. Keep in mind that the cornea is an avascular organ that allows us to directly examine its interior. When blood vessels grow into the cornea and result in leakage and lipid keratopathy, there will be a direct negative impact on the quality of vision.

Argon laser photocoagulation has been used to obliterate these vessels, but a newer direction in improved treatment includes the new technique of photothrombosis. Here, rose bengal dye is injected and laser light is used to create a blood clot that is longer lasting and thus occludes the vessels. Since a photosensitizer is used, less energy is required to occlude the unwanted corneal vessels.

Selective corneal transplantation (SCT) is another area of surgical advancement. Instead of replacing the entire cornea in a penetrating keratoplasty procedure, the surgeon replaces only the diseased portion. If the disease process leaves a scar in the front part of the cornea, an anterior lamellar keratoplasty can be considered.

However, if only the endothelium is diseased, as in Fuchs' corneal dystrophy, then the surgeon should consider a posterior lamellar keratoplasty such as DSAEK or DMEK. When we move from SCT to the refractive surgery arena, we need to focus on not weakening the cornea, as this can have an adverse effect on corneal biomechanics.

If a patient has an epithelial defect that does not heal, the result can be a subsequent corneal melt, corneal thinning (which if left untreated can result in potential corneal perforation) and even blindness. We need to promote the healing of such corneal surface defects in a diabetic or neurotrophic eye. Newer research directions include the use of amniotic membrane extract that is currently being investigated outside the United States.

Treatments in such situations include optimal wetting of the ocular surface with non-preserved tear substitutes, bandage soft contact lenses, amniotic membrane transplant or ultimately a lateral tarsorrhaphy. If the ocular surface is compromised by frequent glaucoma medications containing preservatives, the clinician may need to address this issue by using alternative drugs that cause little or no ocular surface cell damage or recommending glaucoma surgery when indicated; the consequent decrease in the number of glaucoma medications used can possibly improve the health of the ocular surface.

Conclusion

Improving vision is our mission. To achieve this goal we must keep the ocular surface on center stage and do everything possible to boost the health of the eye's surface and thus improve our patients' quality of vision. OM

Thomas John, MD, a world leader in lamellar corneal surgery, is a clinical associate professor at Loyola University at Chicago, and in private practice in Oak Brook, Tinley Park and Oak Lawn, Ill. E-mail him at tjcornea@gmail.com.