Glaucoma Diagnostics

Evaluations of technologies that aid in early glaucoma detection and management.

BY LESLIE GOLDBERG, ASSISTANT EDITOR

Major technological improvements in the diagnostic tools that detect glaucoma and monitor its progression are providing ophthalmologists with new insights for managing this disease. In this article, ophthalmologists evaluate these instruments and provide opinions as to whether these tools have established themselves as today’s standard of care.

GDx

Carl Zeiss Meditec’s (CZM, Dublin, Calif.) GDx technology compares a patient’s retinal nerve fiber layer (RNFL) to a large, multi-racial normative database, while also using neural network techniques to calculate the probability of glaucoma. Study results show that even before visual field loss, the GDx can differentiate between normal eyes and glaucomatous eyes with sensitivity and specificity of 83% and 82% respectively.¹

"The GDx system is useful in the early detection and monitoring of glaucoma," says Douglas P. Webb, M.D., of Cleveland. "It provides us with information that can’t be obtained from visual inspection of the optic nerve, visual field testing or IOP measurements, all of which had been the traditional triad of markers for glaucoma.

"I like the system because it doesn’t just look at the optic nerve — it measures the nerve fiber layer around the nerve," says Dr. Webb. "In addition, the GDx’s comparative studies are very valuable. They are a way for us to both detect glaucoma in patients and also provide a great way to monitor patients as we go forward with their treatment. It really helps us study progression and allows us to see if we have kept eye pressure at the right level."

Dr. Webb, who purchased the system in September 2005, says that his patients have had a positive reaction to the machine. "Patients really appreciate the colorful printouts. The printouts provide them with good visual information and allow patients to get a better understanding of the optic nerve." He also likes that the GDx software has program that provides points of comparison and shows differences between multiple studies.

Stratus OCT

The Stratus OCT (CZM) has three scan protocols to identify and track glaucomatous changes: the optic disc scan, the RNFL thickness scan and the fast RNFL thickness scan.

"The Stratus OCT is a user-friendly machine. It has an intuitive interface, allowing for a small learning curve," says William Wiley, M.D., medical director of the Cleveland Eye Clinic. "Because the OCT is an objective test where an image is acquired quickly and efficiently, it decreases the need for cooperation compared with a field machine. When compared to other nerve analysis machines, the OCT is much less dependent on patient cooperation — making it great to use in the elderly glaucoma population.

"The Stratus does not detect true visual field loss — it detects nerve fiber layer loss, which will correlate with potential visual field defects. With this form of detection, you may have true early detection, which precedes detectable field defects," continues Dr. Wiley. "It has a serial analysis function, allowing for study of specific areas.

The Stratus OCT from Carl Zeiss Meditec.

"The single best feature of the Stratus is the fact that it is both a powerful glaucoma diagnostic tool and a powerful retina pathology diagnostic tool. Beyond that, the Stratus has been an easy tool to transition into the practice providing useful diagnostic information in an efficient manner," concludes Dr. Wiley.

Humphrey Field Analyzer

The Humphrey Field Analyzer (CZM) is a diagnostic tool used to examine a patient’s visual field and is recognized as the "gold standard" in glaucoma diagnosis and management, says Carl Zeiss Meditec.

Douglas R. Anderson, M.D., of the University of Miami School of Medicine Bascom Palmer Eye Institute, has used the Humphrey Field Analyzer "pretty much since it was first available." Prior to that, in clinical practice, he had been using the original Octopus machine, the Goldmann perimeter and the tangent screen.

"The Humphrey Field Analyzer has software capabilities that are not always used," says Dr. Anderson. "including an Overview printout, a Change Analysis printout and a Glaucoma Change Probability Analysis (GPA) printout (the latter an upgraded version of an older Glaucoma Change Probability [GCP] printout). Obstacles to its use are that often if a patient’s care is divided among doctors, they may exchange paper copies of printouts, and for the software to work, test results must be shared in digital form — which is easy, but very rarely done."

Dr. Anderson says that a second obstacle is that the user must exercise some judgment in selecting what pair of fields to use as a baseline. "If one of the first two fields is of poor quality — which it often is for people who have not done the test before — the poor quality early fields need to be eliminated from the analysis. Clinicians who fail to observe which tests are used in the analysis will be misled by the calculated results."

Dr. Anderson says that the Humphrey "is among the few visual field machines that have been optimized and validated. In the United States, it is nearly universal among ophthalmologists, and so data can be exchanged among ophthalmologists for patients who spend part of the year in different locations, move or are obtaining a second opinion."

The Octopus

Haag-Streit’s Octopus Perimetry (Berne, Switzerland) comprises standard white-on-white (SAP), blue-on-yellow (SWAP), Flicker (CFF), manual and automated Goldman kinetic perimetry.

Haag-Streit’s Octopus.

"The original Octopus Perimeter, named the model 201, was manufactured and produced in Switzerland. It was introduced to the United States in the mid-70s and I first used the machine in 1981," reported Marshall N. Cyrlin, M.D., of Associated Vision Consultants. "The machine took up the size of a small room and cost over a hundred thousand dollars at that time. It was a marvel of technology. With the advent of the Octopus it was possible to perform very precise automated static perimetry on patients. The drawbacks to the machine were its size, first generation software and testing time — 30 to 45 minutes."

Dr. Cyrlin noted that the evolution of the Octopus has lead to smaller size, greater affordability and software advancement. "The current Octopus software employs a test strategy called Tendency-Oriented Perimetry (TOP). This testing strategy is extremely efficient and accurate. It allows you to run a test on patients in 3 minutes or less."

PeriTrend, the analysis software widely used on the Octopus, provides users with a way of comparing changes in visual field indices over time. You import test results into Peri Trend and analyze it. I like the software and the choice of printouts."

Dr. Cyrlin believes that the Ocotpus gives users the greatest speed and accuracy combination. "The Octopus can also be used to perform Short Wave Automated Perimetry (SWAP), a more sensitive visual field loss test than white-on-white perimetry to investigate early field loss. It was the first to use SWAP with a fast testing strategy."

MP-1

Nidek’s (Gamagori, Japan) MP-1 microperimeter combines perimetry and fundus imaging to accurately and automatically assess macular/retinal function. Edoardo Midena, M.D., Ph.D., and professor at the University of Padua, Padua, Italy, says, "I have over 7 years experience using the MP-1 microperimeter, and from a technical and clinical application perspective, have found it to be very user-friendly. MP-1 examinations may be customized prior to patient evaluations according to different selectable target strategies." The MP-1 performs a visual field examination according to international standards and each examination is planned according to the patient’s eye disease explains Dr. Midena.

Nidek’s MP-1.

"In a glaucoma practice it is well known that perimetry is still one of the gold standards for the diagnosis and treatment of glaucoma, although the technique is influenced by patient compliance and the exact relationship with tested areas is not fully predictable," continues Dr. Midena. "Morphologic tests are less influenced by patient’s cooperation, but have some limitations which are intrinsic to the individual eye — for example, refractive defects and media opacities."

Dr. Midena explains that with the MP-1, there is an exact topographic relationship between decrease of retinal sensitivity (scotoma) and the involved area, which was previously unavailable. Moreover, he says, when testing during follow-up exam, the test is performed by stimulating exactly the same areas as baseline, which was previously unavailable. "This insures that the changes in sensitivity are now exactly topographically-related," says Dr. Midena. "In addition, the differential map, available at the end of the test, allows the examiner to disclose the individual points where sensitivity is changed. We have recently reported that peripapillary microperimetry may be superior to peripapillary retinal fiber layer thickness in detecting early damages not only in patients with glaucoma, but also in ocular hypertensive subjects."

RTA5

The RTA5 (retinal thickness analyzer) (Marco, Jacksonville, Fla.) system provides multiple diagnostic assessments for early glaucoma detection and management. Its most important characteristic is the ability to assess the complete health of the optic nerve head and macula. Fundus images and real slit-sections are always integrated with thickness, topography, RNFL and dynamic 3D-anatomy imaging modalities.

Marco’s RTA5.

The full posterior pole is examined with overlapping scanning laser ophthalmoscopy (SLO) scans, for the most broad and complete screening for glaucoma, says Marco. Additional, user-defined test patterns allow thorough imaging across the optic nerve head and full peripapillary region. Traditional rim/cup data and temporal-superior-nasal-inferior-temporal (TSNIT) mapping is provided in each patient session. The greatest benefit of the device is that it covers the entire posterior pole — inclusive of the macula and optic nerve head, says Marco.

HRT3

The HRT3 (Heidelberg, Vista, Calif.) assists doctors in the assessment, diagnosis and management of glaucoma patients by using laser technology to produce a topographical image of a patient’s optic nerve, providing an objective analysis of the structure’s cup, rim and RNFL.

Jody Piltz-Seymour, M.D., of Keystone Eye Associates in Philadelphia, has been using the HRT since 1994. "I had one of the original HRT machines which was quite cumbersome. As the upgrades were made to HRT2 and HRT3 the ease of use has significantly improved," says Dr. Piltz-Seymour.

The HRT tracks progression over time and Dr. Piltz-Seymour says that the super pixels that the HRT3 uses can track progression irrespective of the contour line that is drawn. "The HRT3 software upgrades really improve the quality of the progression analyses — I think that this is the strongest feature of the HRT. It is important to make sure that the tests are very accurate. You do not want to track tests that do not have a tight standard of deviation. If the tests are of good quality to them, they can tracked very accurately for progression over time."

Heidelberg’s HRT3.

Dr. Piltz-Seymour says another feature of the HRT is that the software is backward compatible. "With this disease you must be able to track progression over time and you do not want to lose valuable information due to upgrades," she says, emphasizing that clinical examinations are still vitally important and that nothing should replace a good clinical examination.

"The HRT is generally used for two purposes: one to diagnose glaucoma, and two, to check for progression," says Dr. Piltz-Seymour. "In terms of diagnosis, the HRT does not work better than expert examination — but not everyone is an expert."

Dr. Piltz-Seymour does not rely on the HRT to determine if the nerve is abnormal, but says that for those that find it difficult to critically look at the optic nerve, the HRT can be very beneficial. "In terms of diagnostics, I use the HRT more to track progression over time, but it should still not replace a good stereoscopic examination of the optic nerve," she concludes. OM

Reference

1. Medeiros FA, Zangwill LM, Weinreb RN et al. Use of Progressive Glaucomatous Optic Disk Change as the Reference Standard for Evaluation of Diagnostic Tests in Glaucoma. American Journal of Ophthalmology 2005;1010-1018.