Although most studies of diabetic injury to the eye have, understandably, focused on the retina, diabetic damage to the cornea can be significant. Not only can diabetes cause serious corneal morbidity, it weakens the corneal epithelium, leaving it vulnerable to damage from ocular procedures that, ironically, may be performed to treat other diabetic sequelae.
As noted in the last column, the peripheral neuropathy produced by diabetes mellitus does not spare the corneal nerves. Diminished corneal sensation can be measured with an esthesiometer, and structural damage to the corneal nerves can be visualized with confocal microscopy. In addition to the loss of sensation—with implications for the feedback loop that drives tear production—the degeneration of the corneal nerves deprives the stroma and epithelium of trophic support.
Dry eye symptoms are more common in patients with both type I and type II diabetes than in the general population. A German study compared 92 type I and type II diabetic patients (ages 7 to 69 years) to a similar size group of age- and sex-matched controls and found that 53% of the diabetic patients reported dry eye symptoms, versus only 9% of the controls.1
A distinctive form of keratopathy is frequently present in diabetics. First reported more than 30 years ago, this superficial keratopathy is characterized by diffuse punctate staining.2 Eyes with the condition have a tendency toward erosive defects of the epithelium that may occur in response to an insult, such as a therapeutic manipulation of the eye, or an environmental challenge. This epitheliopathy has been noted in patients undergoing vitrectomy, where oftentimes during the procedure the corneal epithelium will cloud, requiring the surgeon to remove the epithelium in order to maintain visualization of intraocular structures. Following epithelial removal, diabetic eyes also take an unusually long time to reepithelialize.
In the epithelium, diabetes produces changes both within the cells and in their attachment to the basement membrane. If one removes the epithelium by scraping a healthy, nondiabetic eye, typically the basal cells will fracture but the basement membrane remains attached to the eye. With diabetic eyes, scraping the surface takes off both the cells and the basement membrane. Although not yet fully understood, something is clearly amiss in the way epithelial cells in diabetic eyes form attachments to the underlying cornea, and this, in turn, may explain the erosive episodes, the ease with which diabetic epithelium can be damaged, and the delayed healing of the surface.
Diabetic keratopathy can manifest as anything from mild corneal damage—equivalent to what one would see in dry eye disease—to severe morbidity, up to and including frank ulceration of the cornea. Although out of the ophthalmologist’s direct control, getting the patient’s glucose level under control is a vital first step in treating diabetic keratopathy.
In caring for the cornea, the goal is to limit further epithelial breakdown. Lubricants, preferably nonpreserved, are necessary. Hyperosmotic dextran solution can be used to reduce the epithelial edema and to provide protection and lubrication. Autologous serum tears may also be used.
Bandage contact lenses are sometimes used to protect the surface, but the caveat here is that one must take great care when using contact lenses in diabetic eyes. In addition to the vulnerability of the diabetic epithelium, the reduced corneal sensation and the frequent dryness of diabetic eyes makes them poor candidates for any kind of contact lens wear.
Patients with diabetic keratopathy need to be monitored carefully. Epithelial defects are common and secondary infection is an ongoing risk, exacerbated by the fact that diabetic individuals tend to have a greater susceptibility to infection. In some cases—eg, where there is a long-term epithelial defect that refuses to heal—it may help to close the lids, either by temporary measures or, if warranted, by lateral lid adhesion (tarsorrhaphy).
The Diabetic Patient
The lesson in all this is that, when examining diabetic patients to look for cataracts and diabetic retinopathy, it is important to also examine the cornea. If there is a planned intervention—eg, cataract surgery or diabetic laser treatment—it is important to be alert to the fact that the diabetic corneal epithelium is poorly equipped to tolerate those insults. Extra care must be taken and prolonged healing time should be expected.
If the diabetic patient is using any topical ophthalmic medications, it will help to prescribe nonpreserved formulations. And, if possible, it is useful to assess corneal sensation in these patients with a Cochet-Bonnet esthesiometer.
Gary N. Foulks, MD, FACS, is the Arthur and Virginia Keeney professor of ophthalmology, University of Louisville, Louisville, KY, and is editor-in-chief of The Ocular Surface.
1. Seifart U, Strempel I. [The dry eye and diabetes mellitus]. Ophthalmologe. 1994 Apr;91(2):235-9. [Article in German]
2. Schultz RO, Van Horn DL, Peters MA, et al. Diabetic keratopathy. Trans Am Ophthalmol Soc. 1981;79:180-99.