Article Date: 6/1/2003

glaucoma care
Revisiting the Existing Standard
After reviewing this pivotal case of a glaucoma patient, you may question the present standard of care.
BY JEROME SHERMAN, O.D.; SHERRY BASS, O.D.; JEFF ROTH, O.D.; DAVID HORN, O.D.; AND HERMINDER BOPARIA, O.D., New York, N.Y.

It's rare for a single case to be so profound that it results in an entirely new standard of care, but it has happened. Read about this case and decide whether it provides ample evidence to begin questioning the present standard of glaucoma care or if it might actually lead to a new standard.

Meeting J.S.

J.S., a 21-year-old white male, first presented to a large teaching facility in 1987. With a family history of glaucoma, intraocular pressures (IOPs) of 20 mmHg OU and cup-to-disc (C/D) ratios of .5 OD and .55 OS, the first O.D. to examine J.S. labeled him as a glaucoma suspect. Over the years, we obtained fields on numerous occasions and included several full-field, 120-degree screenings, 30-2 threshold fields, 24-2 Sita standard fields and an occasional short wavelength automated perimetry (SWAP).

Getting high-tech help

In 1999, one of us referred J.S. for a consultation and for a retinal nerve fiber layer (RNFL) analysis (GDx by Laser Diagnostic Technologies). The referral was based on J.S.'s family history, IOP elevations to the mid- and high-20s, no increase in cupping and essentially normal visual fields.

J.S. presented at the referral without symptoms. A moderate myope (-5.00D), his best corrected visual acuity (VA) was 20/20 OU. Goldmann pressures measured 26 mmHg OU. Cupping was judged as 0.5 vertical in each eye with slightly tilted discs and a temporal crescent OU.

J.S.'s RNFL was considerably thinner superiorly than inferiorly in each eye, and the findings from the left eye were somewhat more abnormal than the right eye. After the GDx exam, the clinician noted that the right field was normal but the left field demonstrated a subtle defect inferiorly (thus corresponding to the superior GDx RNFL thinning) in the left eye only, or the eye with the greater superior RNFL loss. He labeled J.S. as a strong glaucoma suspect and sent him back to the referring doctor.

J.S. returns

In January 2003, J.S. returned for a periodic evaluation. He still had no symptoms, 20/20 VA OU, but Goldmann IOPs were 39 mmHg OU! A record review revealed that he had steadily rising IOPs over the past several years, yet his fields had remained normal OD and still demonstrated a small, inferior defect OS. On only one occasion did a clinician discuss treatment with J.S., but J.S. apparently declined treatment because of his status as a glaucoma suspect only.

Making a diagnosis

With IOPs at 39 mmHg OU, glaucoma was clearly the diagnosis. But were there any other clues? One of us dilated J.S. for stereo disc photos and repeated gonioscopy. Through a widely dilated pupil, and with the use of a three-mirror contact lens, subtle traces of pigment were found on the zonules and exfoliative material observed on the anterior lens capsule eye. The diagnosis was both pigmentary glaucoma and exfoliative glaucoma together, or "Overlap Syndrome."

Note the single abnormal field point inferiorly on the 24-2 VF and the normal 60-4 VF as contrasted with the pronounced RNFL defect superiorly as depicted by the numerous contiguous red pixels in the GDx VCC Sinai deviation map. The HRT II is borderline superiorly.

Treating the problem

After gonioscopy, a retinal tomograph (Heidelberg Retinal Tomograph [HRT] by Heidelberg Engineering) was obtained and analyzed as borderline OU (See figures above and below). We prescribed brimonidine tartrate 0.15% OU and within four days, J.S.'s IOPs dropped to 28 mmHg, and with the addition of bimatoprost 0.03%, his IOPs further reduced to 18 mmHg OD and 16 mmHg OS. We again obtained fields and found them essentially unchanged.

Next we obtained an optical coherence tomograph (Stratus Optical Coherence Tomographer 3 [OCT 3] by Carl Zeiss Meditec), which revealed unremarkable cups in each eye. But the RNFL analysis with the OCT 3 did reveal a TSNIT curve with dips superiorly in each eye (corresponding to the GDx findings).

A repeat GDx was obtained on the same system as before so that change over time data would be available. J.S.'s RNFL loss had occurred almost symmetrically in the superior retina as well as the inferior retina OU. A fourth RNFL analysis, performed with the new GDx VCC, demonstrated a pronounced superior loss in each eye.

Note several abnormal field points inferiorly on the 24-2 VF and larger inferior defect on the 60-4 VF as contrasted with the profound RNFL defect superiorly as depicted by the numerous contiguous red pixels in the GDx Sinai map. The HRT is borderline superiorly.

Getting down to the cause

The undeniable conclusion is that the profound GDx RNFL reduction superiorly OS was responsible for the mild inferior field defect but the somewhat less profound GDx RNFL reduction OD wasn't enough to result in a field defect with either the standard threshold field or with the previous SWAP. Two unrelated technologies, one based on birefringence (GDx) and the other based on optical reflectivity (OCT), yielded synergistic results and are hence more definitive than either one alone.

The term pre-perimetric glaucoma describes a patient who has glaucoma but no detectable field defects. J.S. is an exemplary case, which demonstrates the ability of nerve fiber layer technology to detect RNFL loss OD before visual field abnormalities. In contrast, the apparent lack of increased cupping and lack of progressive visual field loss appears to have resulted in a failure to treat the glaucoma in a timely manner. In effect, cupping and fields belied the serious, progressive and potentially blinding disease. In our experience with scores of cases, central threshold visual fields, long considered the gold standard in the last millennium, often appear insensitive to marked and progressive RNFL loss.

Existing standard of care

None of the clinicians who provided care to J.S. failed to meet the existing standard of care at the time they rendered the care. But J.S. suffered loss of about half of his RNFL in the three-and-a-half-year-period between the two GDx exams. It's unlikely that J.S. will pursue litigation, however if such a case were to go forward, would it lead to a new standard of care for "glaucoma suspects" who have undiagnosed glaucoma?

As a general rule, three conditions must be met to prove culpability in malpractice cases.

1. The care must deviate from the acceptable standard.

2. The patient must suffer a loss.

3. A temporal relationship between the failure to meet the standard and the patient's loss (often referred to as the issue of causation) must exist.

Because J.S. never had any symptoms and both his VA and visual fields are essentially normal, no functional loss has been documented. However, you could argue that he's lost half of each optic nerve and that hence all the redundancy is gone and any further progression will lead to substantive field loss.

The courts set the standard

Helling v. Carey and Keir v. the U.S. were precedent-setting cases in which the courts -- not the eyecare professions -- changed the standard of care. Will we wait for the courts to set a new standard for glaucoma? Or should we evolve a new standard based on this and other similar cases?

Use of these new technologies will likely result in earlier diagnosis and treatment of glaucoma and will simultaneously reduce our risk of malpractice litigation. Keep in mind though that if, for example, a patient is suspect of having a choroidal neovascularization membrane (CNVM), then the clinician must obtain a timely fluorescein angiogram (or even an indocyanine angiogram) regardless of whether one is available. Referral for such procedures, or having the necessary equipment periodically brought into the office (in a timely manner) is the standard.

The future standard

The major implication of this case is that automated visual fields, performed at threshold, aren't the best technology to detect early and even moderate damage to the optic nerve in glaucoma, nor is the ophthalmoscopic evaluation of the discs. Although the authors readily admit that a single case won't create a precedent (unless perhaps a similar case results in successful litigation), there is now ample evidence to at least begin questioning the present standard of care in glaucoma.

With the myriad of high-tech devices already on the market and many more to come in the near future, providing quality care becomes remarkably complex. As doctors, it's our responsibility to provide the best care. As patients, we all wish to have the best possible care provided to our families and ourselves.

Dr. Sherman practices at the Eye Institute and Laser Center in Manhattan and is a distinguished teaching professor at the SUNY College of Optometry. All of the authors are involved in clinical care, clinical teaching or research within the Glaucoma Institute of the SUNY College of Optometry.

 

Reviewing the Technology

Here's a brief listing of instruments that analyze the optic nerve and its surrounding peripapillary tissue.

Stratus OCT. The Stratus Optical Coherence Tomographer (OCT) by Carl Zeiss Meditec uses the echo delay time of light back-scattered from various layers of the retina to create a 2-D, cross-sectional image of ocular tissue.

HRT II. Heidelberg Engineering's Retinal Tomograph II (HRT II) uses a confocal scanning laser to measure a patient's optic nerve and nerve fiber layer. It displays the depth and shape of the optic nerve cup and provides detailed information about the neuroretinal rim, notching and nerve fiber degeneration.

GDx. Laser Diagnostic Technologies' GDx is a confocal scanning laser polarimeter that indirectly measures nerve fiber layer thickness. It detects nerve fiber loss, not vision loss.

RTA. Talia Technology's retinal thickness analyzer (RTA) uses a narrow slit of a helium neon laser beam to identify the nerve fiber layer and the retinal pigment epithelium, calculating the difference between the two to reflect the retinal thickness.

 


Optometric Management, Issue: June 2003