Other than central corneal thickness (CCT), the cornea may not immediately come to mind when managing glaucoma patients. However, there are many reasons not to overlook the possibility of anterior segment disease.
The Ocular Hypertension Treatment Study (OHTS) showed that 24% of patients who had ocular hypertension had pachymetry measurements greater than 600m.1 Also, patients who had thin corneas and elevated IOP had a significantly higher risk of developing glaucoma.2
Beyond the findings of OHTS, several anterior segment diseases have a high correlation to glaucoma, particularly secondary glaucomas.
ICE Syndromes
The iridocorneal endothelial (ICE) syndromes include essential iris atrophy, Chandler syndrome and Cogan-Reese (iris nevus) syndrome. These conditions are asymmetric and often unilateral. They appear most commonly in white females between the ages of 30 and 40 and result in loss of vision from endothelial compromise and/or glaucoma.3
They appear with a hammered silver endothelium and associated corneal edema, iris atrophy with correctopia, prominent iris nevi and, eventually, peripheral anterior synechia. This is followed by angle closure and glaucoma.4
All three conditions are proliferative endothelial degenerationsan abnormality of the endothelial cells that results in a histology similar to that of epithelial cells.5 Histological examination of the corneas of three patients who had ICE and underwent penetrating keratoplasty revealed multilayered endothelial cells with epithelial features (microvilli).5
This abnormal endothelium then migrates across the corneal surface, inner surface of the trabecular meshwork, the anterior iris surface and zonular fibers.6 This results in corneal edema, secondary glaucoma, nevi, noduli, atrophy of the iris and pupillary distortion.
This patient presented with significant uveitis and herpes simplex disciform stromal keratitis. |
Of 25 patients with glaucoma, the diagnosis of ICE syndrome was overlooked initially in 17 (68%).
Medical treatment of glaucoma in these patients was generally ineffective. Of 22 patients who underwent surgery, 10 required more than one procedure.
Even with treatment, 11 patients (44%) developed visual field loss.
Endothelial Dystrophies
Posterior polymorphous dystrophy (PPMD) manifests as localized vesicular or band patterns with localized lesions that resemble craters. It is associated with Descemets haze, deep stromal haze, peripheral iridocorneal adhesions and glaucoma.9 Unlike the ICE syndromes, PPMD is bilateral. Histologically, epithelial-like cells are the most predominant cells in the endothelium.10
As many as 40% of patients who have PPMD develop glaucoma as the abnormal endothelial cell layer covers the posterior cornea and then grows across the trabecular meshwork and onto the iris.11 Glaucoma development can be as high as 66.7% of patients who have PPMD and visible iridocorneal adhesions.10
Congenital hereditary endothelial dystrophy (CHED) is rare and presents at birth or shortly afterward.12 One study revealed complete absence of the endothelial layer in patients who had CHED. This led to total corneal opacification. The researchers found that CHED was associated with congenital glaucoma.13
Herpetic Eye Disease
Two more common conditions that occur in healthy individuals, herpes zoster ophthalmicus (HZO) and herpes simplex uveitis (HSV), have a high association with glaucoma.14 Ocular findings associated with HZO include pseudodendrites, iritis and conjunctivitis, but also extend to nerve palsies and even glaucoma. In one study, iritis occurred in 43% of HZO cases, and there often was a corresponding elevated IOP.15 More than 56% of the patients who had HZO and iritis developed glaucoma during the 10-year retrospective study.15
Another study found that secondary glaucoma was the most frequent complication of HZO and HSV, occurring in 54% of HZO patients and in 38% of HSV patients.16 More than 20% of HSV patients and 21% of HZO patients were legally blind at completion of the study.
One study suggests that the high incidence of glaucoma here is due to damage of the trabeculum by the HSV infection.17 In this study, primary cultures of human trabecular meshwork cells demonstrated the ability of HSV-1 to enter into and establish a productive infection of the trabeculum, leading to elevated IOP.
As clinicians, we cannot ignore the possibility of anterior segment disease when managing glaucoma patients. We should educate our patients about the need for frequent monitoring for glaucoma after treatment or diagnosis of any of such conditions.
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