ANNUAL DIAGNOSTIC TECHNOLOGY ISSUE

SUSS OUT THE SILENT THIEF

USE THE FOLLOWING ADVANCED DEVICES TO PUT THE DIAGNOSTIC PUZZLE OF GLAUCOMA TOGETHER

Justin Schweitzer, O.D., F.A.A.O., Sioux Falls, S.D.

GLAUCOMA, LIKE a large puzzle, has many pieces that must be put together to make a proper diagnosis and initiate management. The disease, at times, can be easily diagnosed because the patient has an IOP of 28 mmHg, a visual field defect and the death of retinal nerve fiber layer (RNFL) axons. But, many times, diagnosis isn’t that simple.

Here, I discuss the four advanced diagnostic technologies to consider to help put the final pieces of the glaucoma puzzle together.

OCT/SD-OCT

The measurement of the circumpapillary RNFL via OCT is a well-established and widely used diagnostic marker for glaucoma.

SD-OCT has revealed two new diagnostic parameters for glaucoma: (1) the ganglion cell inner plexiform layer (GCIPL) and the ganglion cell complex (GCC) thickness, which comprise ganglion cell analysis. Studies in Investigative Ophthalmology & Visual Science and the American Journal of Ophthalmology on the GCIPL and GCC in the macular region show both parameters are likely as sensitive as circumpapillary RNFL analysis in glaucoma detection. Specifically, the ganglion cell layer is thickest in the perimacular region, and decreased total macular thickness is seen in glaucomatous eyes, likely due to ganglion cell layer thinning.

Devices can help you construct the glaucoma puzzle.
Clinical image courtesy Sherrol Reynolds, O.D., F.A.A.O.

Clinical pearl: Studies in the Journal of Glaucoma and the British Journal of Ophthalmology discuss the advantage of using both ganglion cell analysis and circumpapillary RNFL measurements to assist in making a comprehensive glaucoma diagnosis.

Billing: OCT and SD-OCT are considered scanning computerized ophthalmic diagnostic imaging (SCODI) tests. The CPT code 92133 is defined as a SCODI test, posterior segment, with interpretation and report, unilateral or bilateral; optic nerve. The code is used to follow glaucoma suspects, diagnose glaucoma, monitor glaucoma treatment and detect glaucoma progression.

OCULAR RESPONSE ANALYZER

This device (Reichert Technologies) assesses corneal hysteresis (CH) to determine glaucoma risk and disease progression. Specifically, CH is the difference between the pressure at which the cornea bends inward during an air jet applanation and the pressure at which it bends out again. The difference, measured in mmHg, determines the bio-mechanical property of the cornea relating to its elasticity.

A 2008 study in Investigative Ophthalmology & Visual Science reveals that when IOP is elevated, the optic nerve in patients with a high CH bows back more than the optic nerve in people with a low CH. As such, low CH values (explained below) are associated with greater glaucoma risk. A 2008 study in Investigative Ophthalmology & Visual Science reveals that when IOP is elevated, the optic nerve in patients with a high CH bows back more than the optic nerve in people with a low CH. As such, low CH values are associated with greater glaucoma risk. In addition, a 2010 study in Investigative Ophthalmology & Visual Science on asymmetric primary open-angle glaucoma shows CH is the only factor different between eyes — 8.2 and 8.9 in higher and lower grades of glaucoma, respectively. Further, a 2012 study in the Journal of Glaucoma shows glaucomatous eyes with low CH are not only at a higher risk for progression, but also progress at a faster rate.

Clinical pearl: Studies in Ophthalmology and Investigative Ophthalmology & Visual Science of healthy subjects show that mean values for CH fall in the range of 10.1 mmHg to 10.9 mmHg, with normal ranging between 8 mmHg to 14 mmHg. In my practice, we use a semi-quantitative scale of low, (CH < 8 mmHg), medium (CH 8-12mmHg) or high (CH > 12 mmHg), based on discussions we’ve had with other eye care providers.

Billing: The CPT code for measurement of corneal hysteresis is 92145, a Category I CPT code. As of January, it replaced the temporary Category III CPT code, 0181T.

VISUAL EVOKED POTENTIAL (VEP) DEVICE

VEP is an objective measure of visual function that assesses the electrical activity of the cerebral cortex by having the patient view standardized visual stimuli while wearing scalp electrodes. The clinician assesses the amplitude and latency of the VEP waveforms. These waveforms are affected by various conditions of the visual pathway, including glaucoma.

Clinical pearl: A 2011 study in the Journal of Glaucoma described delayed latency and reduced amplitudes on VEP printouts targeting the magnocellular and parvocellular ganglion cell pathways in patients with asymmetric glaucoma and worse visual field mean deviation.

Billing: The CPT code for VEP is 95930 and is defined as “bilateral,” so reimbursement is for both eyes.

PATTERN ELECTRORETINOGRAM (PERG)

PERG electrodes are placed in standardized positions on the scalp, and information about macular electrical activity is gathered as the patient looks at a contrast-reversing stimulus.

Studies in Investigative Ophthalmology & Visual Science show that in early stages of glaucoma, the PERG signal from the retinal ganglion cells diminishes at a rate that exceeds the expected loss from the ganglion cell axon structure. This correlates with the RNFL loss observed on OCT.

Clinical pearl: When a glaucoma suspect or a glaucoma patient demonstrates abnormal PERG amplitudes, it is reasonable to monitor him or her more carefully, as these patients have a higher rate of RNFL thinning and progression, studies show.

Billing: The CPT code for PERG is 92275 and must be supported by a glaucoma diagnosis code.

Remember, the patient’s medical record must contain documentation that fully supports the medical necessity for the use of all these devices when applying for reimbursement.

MAKING THE PIECES FIT

Glaucoma, at times, can be a puzzling disease. One diagnostic test is not sufficient to aid in making an accurate diagnosis. When a wide variety of the diagnostic tools available are utilized, piecing the glaucoma puzzle together becomes possible, and doctors have a better chance of staving off vision loss. OM

DR. SCHWEITZER specializes in advanced glaucoma, refractive surgical clinical care and anterior segment pathology at Vance Thompson Vision. He has had multiple articles published and has delivered lectures on glaucoma, anterior segment pathology, refractive surgical clinical care and surgical management. Email him at justin.schweitzer@vancethompsonvision.com, or send comments to tinyurl.com/OMcomment.