Perimetry still recommended for glaucoma management

Recent data show a dramatic decrease in visual field testing, despite no change in clinical practice guidelines.

Murray Fingeret

by Murray Fingeret, OD

When I am speaking on diagnosing glaucoma, I usually begin with a discussion of what constitutes the glaucoma work-up.

I would describe the following tests/procedures that should be included: history, visual acuity, intraocular pressure measurement, pachymetry, gonioscopy, dilated optic nerve/retinal nerve fiber layer examination and a threshold visual field test. Documentation of the optic nerve/retinal nerve fiber layer (RNFL) is required (such as with photography or imaging), but imaging using a device such as the Heidelberg Retina Tomography (HRT, Heidelberg Engineering) or optical coherence tomography is not necessary if some other form of documentation is performed.

Testing schedule

These tests are done at the time of diagnosis and periodically thereafter. The interval for testing will vary based upon the patient’s characteristics (age, history, IOP level, extent of damage) and how the clinician chooses to manage the individual.

Traditionally, fields and imaging are done on a yearly basis for diagnosed glaucoma patients, with the interval shortened if change is suspected or greater severity is present. According to Chauhan, recent papers illustrate the need to do more tests earlier so that the statistical software packages available with perimetry or imaging will be more robust.

For example testing may be done at the time of diagnosis, at 6 months, 12 months, 18 months and 2 years post diagnosis. This gives five tests, and if stability is present at this point, the interval can be reduced to 1 year. However, if there are questions of progression, twice yearly testing is indicated. Approximately 10% of newly diagnosed patients progress rapidly, and without an ample number of tests it would be difficult to recognize which newly diagnosed patient fits into this category, report Leske et al. and Heijl et al.

Against the backdrop of what constitutes the glaucoma examination is a change that has occurred within ophthalmic testing. The quality of OCT has improved dramatically over the last 4 years. OCT was introduced almost 20 years ago, with the third generation evolving from time to the spectral domain (Fourier) format with improved speed and resolution. Approximately three-fourths of eye care practitioners have or have access to imaging devices. This is also a change from just a few years ago.

We come to the point of this column: Has imaging improved so much that we no longer require perimetry to diagnose and manage glaucoma? Can we now rely only on the structural evaluation of the optic nerve, RNFL and macula region?

Visual field testing data

At the recent American Glaucoma Society annual meeting, Joshua Stein, MD, presented a fascinating paper discussing trends in the use of instrumentation in clinical practice. Dr. Stein analyzed claims data from a large U.S. managed care plan. All individuals whose data was included had a diagnosis of open-angle glaucoma as recorded on the claims form, and 169,917 individuals older than 40 years were evaluated.

The odds of a patient undergoing visual field testing decreased 35% from 2001 to 2005, decreased 13% further from 2005 to 2009, with an overall 43% decrease in visual field testing from 2001 to 2009. By contrast, ophthalmic imaging increased in use 102% from 2001 to 2005, 22% further from 2005 to 2009 and 146% overall from 2001 to 2009. By 2008, the probability of a patient having imaging performed was greater than perimetry.

Also, as a side note, fundus photographs were billed infrequently, from 15% to 24% depending whether an optometrist or ophthalmologist was submitting the claim. In regard to perimetry, 80% of individuals seen exclusively by a glaucoma specialist had perimetry performed on a yearly basis.

Decrease in field testing

This trend is seen when data was separated by optometry and ophthalmology, with data similar, though not identical. What can be made of this? If accurate, this goes against the preferred practice guidelines for both optometry and ophthalmology, which recommend perimetry to be done in addition to optic nerve/RNFL documentation on at least a yearly basis. Are clinicians not performing perimetry as often or not at all now that they have an imaging device? Could it be that clinicians are not forgetting about perimetry but simply doing them less often?

Could this relate to reimbursement issues? Up until recently, imaging received a higher reimbursement than perimetry. One recent change is that the reimbursement for imaging was reduced by Medicare by about 50%. It would be interesting to re-evaluate the data going forward and see if there is a change back in the direction of perimetry, or perhaps this is simply a billing issue and does not represent what is being done in practice. For example, many insurance carriers will reimburse only for one test per visit. Perhaps clinicians are doing both but only billing for the higher reimbursed service.

Visual fields are needed along with optic nerve assessment to diagnose and manage glaucoma. While optic nerve/RNFL damage tends to occur earlier in the natural history of the disease, both structure and function need to be assessed to understand the severity and stability of the condition. I could not imagine having to diagnose and follow individuals with glaucoma without a visual field.

There are a number ways to view this issue. Medicolegally, visual fields are considered part of the evaluation for individuals with glaucoma. The practice pattern guidelines for optometry and ophthalmology recognize the need to perform perimetry periodically for individuals with glaucoma.

What about from a practical viewpoint? Are doctors sensitive to patient’s complaints about perimetry? Could this explain why visual fields are not being done as commonly as before? Has OCT gotten so good that we do not need perimetry? Do some clinicians believe that patients can be managed without perimetry without a loss in the quality of care? Or are clinicians putting too much value in imaging?

Is this a trend we should be concerned about? It is difficult to understand if clinicians are performing visual fields less or simply not billing for them. If it is the former, then we need to educate clinicians better as to the importance of perimetry. Also further study is needed to understand if we can modify our traditional routines as more advanced diagnostic technologies become available.

References:

• Chauhan BC, Garway-Heath DF, Goñi FJ, et al. Practical recommendations for measuring rates of visual field change in glaucoma. Br J Ophthalmol. 2008;92(4):569-573.
• Leske MC, Heijl A, Hyman L. Ophthalmology. Predictors of long-term progression in the early manifest glaucoma trial. 2007;114(11):1965-1967.
• Heijl A, Bengtsson B, Hyman L, Leske MC; Early Manifest Glaucoma Trial Group. Natural history of open-angle glaucoma. Ophthalmology. 2009;116(12):2271-2276.
• Stein JF, Talwar N, Laverne AM, Nan B, Lichter PR. Changes in the diagnostic evaluation of patients with open-angle glaucoma from 2001-2009. Presented at the American Glaucoma Society Annual Meeting, March 2011.

• Murray Fingeret, OD, is chief of the optometry section at the Department of Veterans’ Affairs Medical Center in Brooklyn and Saint Albans, N.Y., and a clinical professor at SUNY College of Optometry. He is also a member of the Primary Care Optometry News Editorial Board. He may be contacted at St. Albans VA Hospital, Linden Blvd. and 179th St., St. Albans, NY 11425; (718) 298-8498; fax: (516) 569-3566; murrayf@optonline.net.
• Disclosure: Dr. Fingeret is a consultant for Carl Zeiss Meditec and is on the speakers bureau for Carl Zeiss Meditec, Heidelberg Engineering, Optovue and Topcon. He has received research support from Carl Zeiss Meditec, Heidelberg Engineering, Optovue and Topcon.