WHEN FACED WITH BORDERLINE CASES, TURN TO THESE TWO TESTS
A 65-YEAR-OLD white female patient presents for her comprehensive eye exam. Her IOPs measure 26 mmHg OU; corneal pachymetry measures 550 OU; and her optic nerve heads are suspicious for glaucoma. VF testing is normal, and OCT shows marginal thinning of the retinal nerve fiber layer (RNFL) in one quadrant. How do you proceed?
Here, I discuss two clinical tests that can help you decide.
CORNEAL HYSTERESIS (CH) TEST
The CH test reveals the ability of the cornea to absorb and dissipate energy. CH is reflective of overall ocular tissue properties and associated with optic nerve changes, suggest studies in Investigative Ophthalmology & Visual Science and Graefe’s Archive for Clinical and Experimental Ophthalmology.
The average CH in normal eyes in the United States is 10.5 mmHg. Corneas that have CH levels above this absorb or dissipate energy well, while those below it do not and, therefore, have been shown associated with or predictive of glaucoma development and progression.
In fact, each 1 mmHg lower CH was linked with a 22% increase in glaucoma development risk, independent of age, IOP and central corneal thickness, reports a 2016 Annual Meeting of the Association for Research in Vision and Ophthalmology study.
(Must be supported by a glaucoma diagnosis code.)
PATTERN ELECTRORETINOGRAPHY (PERG)
PERG testing shows retinal ganglion cell function via sensors placed on the lower eyelid. As damage to the retinal ganglion cells has been shown to precede optic nerve head and RNFL structural changes, PERG testing is important.
Glaucoma suspect patients who demonstrate abnormal PERG amplitudes have a higher risk and rate of RNFL thinning vs. those who do not. In addition, PERG results have been shown to detect early states of glaucoma before the onset of VF defects and RNFL loss.
If the 65-year-old patient has an above normal CH and normal PERG testing, monitoring would be reasonable. If, however, either or both of her CH or PERG testing is abnormal, a more aggressive treatment and follow-up plan should be considered. OM