The most anterior, clear portion of the eye is called the cornea. It is the first structure light traverses on its way into the eye. Any condition that affects the cornea can affect the cornea’s ability to help focus light on the retina, and thus affecting one’s ability to obtain a clear image. Since the cornea creates two thirds of the focusing power of the eye, even a small change in the cornea may lead to changes in one’s vision. Conditions of the cornea may be treated with medications or surgery.
Due to the desert environment we live in, many people suffer from a feeling of eye dryness, or “dry eye.” Symptoms range from an irritated eye in certain conditions to blurriness, redness and foreign body sensation. These symptoms may only mildly interfere with one’s life or in some cases cause a severe disability. This irritation of the surface of the eye can have many different causes, and is important for us to determine which ones apply to you. A variety of treatment options are available, the choice of which depends on the severity of the disease and what is seen on examination.
Inflammation may affect the conjunctiva, a highly specialized skin covering the front of the eye. It may be caused by allergies, reactions to chemicals or infections. Infections may be caused by viruses, fungi, bacteria or protozoa. If the infection affects the cornea, it may cause a corneal ulcer. Corneal infections are associated with redness, pain, light sensitivity, and reduced vision in the affected eye. Any infection in the cornea can lead to scar formation. Scarring can reduce the quality of vision, so prompt diagnosis and treatment of infections is critical. Risk factors for corneal infections include contact lens wear, injury or eye trauma.
Fuchs’ dystrophy is a non-inflammatory, inherited condition that may be progressive and may affect both eyes. The internal cell lining of the cornea, called the endothelium, becomes damaged. If the endothelium does not function properly, fluid accumulates in the cornea, which causes clouding and a slow decrease in vision. Initially patients will notice blurred vision in the morning and a glare or halos around lights. As the dystrophy progresses, one’s vision can be blurred all day long. Early Fuchs’ dystrophy can be treated with hypertonic saline drops to help remove excess fluid from the cornea. In more advanced cases, surgery to replace the damaged cells may be necessary.
Keratoconus is a common corneal condition in which the cornea begins to thin. As it thins, it loses strength, and aspects of the cornea start to bulge. The cornea changes into an abnormal shape, and one’s vision becomes affected. Initially, the vision can be corrected with glasses or contact lenses. If these are no longer effective, surgical intervention may be necessary. The options range from prescribing glasses, contact lenses, implantable corneal ring segments (called Intacs) to a corneal transplant. Newer treatment options that are being studied include crosslinking (a way to halt or slow down keratoconus) and topography guided ablation. Barnet Dulaney Perkins is currently studying crosslinking as a way to treat keratoconus. Approximately 20% of patients with keratoconus seeing a corneal specialist will eventually need a partial or full thickness corneal transplant in order to restore good vision.
A full thickness corneal transplant can be used to treat a wide variety of corneal conditions. In the standard method of performing this procedure, a hand-held surgical blade called a trephine is used to remove a button-shaped section of the central cornea that consists of all the corneal tissue layers. The button is replaced with healthy donated corneal tissue (a graft) from an eye bank. The transplanted tissue is typically sutured into position. The full thickness corneal transplant is an excellent tool for restoring vision, but recovery of best vision can take 6 or as long as 12 to 18 months.
A recent development in full thickness corneal transplants is the use of a femtosecond laser to assist with the procedure (femtosecond laser-assisted keratoplasty). The surgeon programs the laser to create precisely shaped incisions, much more intricate than can be accomplished with a trephine, around the edges of the patient’s central cornea and the donor tissue. The incisions interlock like puzzle pieces, allowing the donated tissue to fit snugly on the eye. This has several advantages compared with a full thickness corneal transplant performed with a trephine. Fewer sutures can be used, and they usually can be removed sooner. The graft is more stable and tends to heal more quickly. The eye tends to heal more evenly as well, which results in a less irregular corneal shape, less astigmatism and therefore better vision.
Femtosecond laser-assisted keratoplasty is not for every patient. The peripheral cornea must be clear enough for the laser to properly create the incisions. A detailed analysis of the cornea with specialized imaging devices can determine whether a patient is a good candidate for the procedure. For those who are not good candidates for femtosecond laser-assisted keratoplasty, a standard corneal transplant can still be performed.
Instead of replacing the full thickness of the cornea, some patients benefit from a partial replacement. Two types of partial thickness corneal transplants exist. In deep anterior lamellar keratoplasty, or DALK, only a very thin layer of tissue is left and the rest is replaced with donor tissue. Visual rehabilitation is similar to a full thickness corneal transplant. The advantage of a DALK is the lower rate of rejection as compared to the full thickness transplant. In descemet’s stripping automated endothelial keratoplasty, or DSAEK, a smaller amount of tissue is transplanted. This more recently developed technique offers faster visual recovery for patients with corneal swelling caused by endothelial conditions such as Fuchs’ dystrophy. Only a very thin layer of cornea is removed and then replaced with a thin layer of donor cornea. Vision can be restored as quickly as 2 to 3 months.