Winter Update 2009: treatment considerations for glaucoma suspects

The sooner the detection of and treatment for glaucoma begins, the better the prognosis, said Douglas J. Rhee, M.D., assistant professor, Massachusetts Eye and Ear Institute, Harvard Medical School, Boston, at the American Society of Cataract and Refractive Surgery’s Winter Update meeting earlier this year.
Since current methodologies for diagnosis and identification of disease are incapable of detecting the earliest change, a large number of patients fall into the category of “glaucoma suspects,” he said.
Some glaucoma suspects will proceed to identifiable damage while others do not have disease, Dr. Rhee said. However, most will never develop disease. To further complicate the situation, ocular hypertension (IOP > 21 mmHg) can either be a normal finding or a pre-cursor to disease, he explained.
In its early stages, clinicians have to make the difficult decision as to whether or not the patient should be treated. Following the affirmative, there is a general agreement that the IOP lowering target is modest, Dr. Rhee said. The conditions, which span the early spectrum of disease, are ocular hypertension, low tension glaucoma suspect, pre-perimetric glaucoma, and early glaucoma.

Technologies and tests

Technologies that measure structural parameters of the optic nerve and retinal nerve fiber layer can distinguish glaucoma earlier than automated achromatic visual field (AAVF) testing (i.e. white on white visual field), Dr. Rhee said. These technologies have led to the concept of pre-perimetric glaucoma-a disease state in which structural evidence of disease exists in conjunction with an AAVF that shows no abnormalities, he xplained.
Other psychophysical tests, such as frequency doubling and short wave automated perimetry, may have greater sensitivity than AAVF. However, specificity has been a difficulty, he said.
Still, there is no one test that defines glaucoma. Therefore, the clinician remains the “gold standard” for determining the presence of disease by integrating and interpreting all of the information.

Ocular hypertension

Other than an elevated IOP of greater than 21 mmHg, Dr. Rhee said that clinical presentation of ocular hypertension also includes the detection of an open anterior-chamber angle on gonioscopy. Clinicians will also find the absence of characteristic optic nerve appearance which is: documented thinning of the neurosensory rim over time, acquired pit or notch of the neurosensory rim, disc hemorrhage that crosses the disc margin (i.e. Drance hemorrhage), cup/disc asymmetry greater than 0.2 in the absence of a cause such as anisometropia, bayoneting of a blood vessel (quick angulation in the course of the blood vessels as they exit/enter the nerve), violation of the “ISNT” rule of neuroretinal rim thickness (from thicker -> thinner rim): inferior greater than superior, greater than nasal greater than temporal, and retinal nerve fiber layer loss (suggestive, but not specific for glaucoma). There is also an absence of characteristic visual field loss.
Using results of the Ocular Hypertension Treatment Study (OHTS) as guidance on treatment, Dr. Rhee briefly summarized the OHTS. The study set out to determine the efficacy of topical medications in preventing or delaying the onset of visual field (VF) loss and or optic nerve (ON) damage in patients with ocular hypertension. Patients with pseudoexfoliation or pigment dispersion were eliminated from the study. Between February 1994 through October 1996, 1637 subjects were enrolled. The mean age of participants was 55 years with 57% being women and 25% being Afreican American. The baseline IOP was 24.9 +/– 2.7mmHg and the mean cup/disc ratio was 0.36 +/– 0.18.
The major findings of the study included the fact that lowering IOP decreased the relative risk of developing primary open angle glaucoma (POAG) by 54%; absolute risk was reduced from 9.5% in the observation group and 4.4% in the treatment group at 5 years. The researchers also found that older age, larger vertical c/d ratio, higher IOP, greater PSD and thinner CCT predict greater risk.
Interesting findings included the fact that the mean reduction in medication group was 22.5+/– 9.9% (4.0 +/– 11.6% in observation group), 40% required two topical medications; 9.3% required three topical medication, 50% progressed by ON criteria and diabetes was not a risk factor for developing POAG (but diabetes with BDR were excluded).

Low tension glaucoma suspect/physiological cupping

Dr. Rhee defined low tension glaucoma suspects as those whose IOP measurement are less than 21 mmHg and have an absence of pathologic characteristics of the optic nerve, retinal nerve fiber layer, or functional deficits of the visual field that localize to the RNFL. However, there is a c/d ratio greater than 0.6, he said.
In such cases, he said, generally no treatment is needed if there are no pathological signs. However, follow up should include periodic IOP measurements (Q6-12 months), structural imaging (Q6-12 months), visual field (Q6-24 months), he said.

Pre-Perimetric Glaucoma

In defining pre-perimetric glaucoma, Dr. Rhee said there is the presence of characteristic structural damage of the optic nerve, but the absence of a visual field change. RNFL defects are suggestive of glaucoma, but are not specific. There is no IOP criterion—i.e. the IOP can be low or high.
Dr. Rhee said this condition is glaucoma and that the IOP target should be approximately 30 percent. Follow up should include periodic IOP measurements (Q3-4months), structural imaging (Q6-12 months), visual field (Q6-12 months), he said.
For early glaucoma, Dr. Rhee defined it as the presence of characteristic structural damage of the optic nerve, and the presence of a visual field change. RNFL defects are suggestive of glaucoma, but are not specific. There is no IOP criterion—i.e. the IOP can be low (LTG) or high (POAG).
In this case if the clinician is unsure if there is disease, Dr. Rhee said they can try using one or two of the newer diagnostic technologies available and if tests are negative, then the clinician can be reassured but if results are positive, then they may want to follow the patient more closely.
Dr. Rhee stressed that these considerations for management are general suggestions and that individual patients may require modifications.

Editors’ note: Dr. Rhee has financial interests with Alcon (Fort Worth, Texas), Allergan (Irvine, Calif.), and Pfizer (New York).

Contact information:

Rhee: 617-573-3670, dougrhee@aol.com