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HomemiequipmentZeiss: Leading the Way in Glaucoma Management

Zeiss: Leading the Way in Glaucoma Management

ZEISS has been a leader in glaucoma management for almost 30 years, beginning with the first Humphrey Field Analyser released in 1984. Since then, ZEISS has introduced many outstanding glaucoma technologies; some of the most important of which are described below.

Humphrey Field Analyser

The Humphrey Field Analyser (HFA) remains the Gold Standard in perimetry. It is used by tens of thousands of clinics around the world and many major clinical studies have relied upon its results.

One of the major benefits of the HFA is its Guided Progression Analysis (GPA) software. This software is designed to overcome the difficulty of identifying whether a change in the visual field is due to disease progression or simply due to normal variability. Since visual fields in glaucoma patients vary more than in normal patients, this is not an easy task, so the developers of GPA had to define what the normal range of variability in stable glaucoma patients actual is. They achieved this by gathering test-retest data from 363 well-managed glaucoma patients from 16 centres in three continents, thus establishing a range of variability beyond which could be defined as statistically significant glaucoma progression.

This is certainly valuable information; however the next step was to use GPA to define the rate of progression. This has always been problematic since advancing cataract can confound progression analysis. The GPA developers have overcome this issue by creating an additional parameter called the Visual Field Index (VFI). The VFI is based on an intuitive percentage scale and filters out the effects of cataract, making it an ideal parameter for measuring the rate of change. So GPA not only tells you if statistically significant disease progression is occurring, it also tells you the rate of progression – very important parameters when making important treatment decisions

The Humphrey Field Analyser (HFA) remains the Gold Standard in perimetry”

Humphrey Matrix

The Humphrey Matrix uses frequency-doubled stimuli instead of standard automated perimetry to establish the visual field. This stimulus is very effective at detecting glaucoma at an early stage; in some cases earlier than standard automated perimetry. The Matrix has been widely researched in the peer-reviewed literature and its performance in glaucoma is well established, but at the same time it is also very easy to use. It fits neatly into small clinics and is extremely fast with the basic screening test taking around 40 seconds per eye in most cases. It also doesn’t require a darkened room, nor does it require refractive correction for most patients. Recently, a chin rest and networking options have been added for further convenience.

CIRRUS HD-OCT

The CIRRUS HD-OCT allows clinicians to measure the RNFL, the optic nerve head and the ganglion cell/inner plexiform layer parameters with a high degree of repeatability. For example, by automatically centring the RNFL measurement, the CIRRUS has been shown to be accurate and repeatable with a standard deviation of 1.3 to 1.9 microns1,2.

Optic nerve head parameters are very important and the CIRRUS performs this function with excellent results. It establishes the disk area very accurately using Bruch’s Membrane and measures the parameters in the same plane as the optic nerve head, thus giving more realistic results on eyes with tilted disks. Interestingly, during development, the ZEISS scientists found that disk area was more important than age when establishing the normative data, therefore the results are both age and disk area-matched.

The ganglion cell analysis also gives valuable information and is unique in two ways. Firstly, it excludes RNFL from the analysis, therefore removing one possible source of confounding variability. Secondly, it centres the analysis exactly on the fovea using the FoveaFinder software. This is important since patients often fixate poorly – by not relying on correct fixation, the CIRRUS gives a more reliable result.

The CIRRUS HD-OCT also features Guided Progression Analysis. It works in a similar way to the Humphrey Field Analyser in that it takes into account the test-retest variability of the CIRRUS and only flags progression if there is change beyond this amount.

Combined Analysis

The Humphrey Field Analyser and the CIRRUS HD-OCT can now effectively combine their raw data with one another, giving clinicians additional insight into the structure/function relationship of glaucoma. Based on the work of Garway-Heath et al3 and Hood et al4 the new Combined Analysis displays show the relationship between the CIRRUS optic disk cube and ganglion cell analysis to HFA visual fields.

Contact Details
40 – 52 Talavera Road
North Ryde NSW 2113
Contact: Customer Service
T 1300 365 470 or 02 9020 1333
(NZ) 0800 334 353
W www.zeiss.com.au
E [email protected]

References

1. Vizzeri et al. Agreement between spectral-domain and time-domain OCT for measuring RNFL thickness. Br J Ophthalmol. 2009;93(6):775-781

2. Leung, C et al. Retinal nerve fiber layer imaging with spectral domain optical coherence tomography: a variability and diagnostic performance study. Ophthalmology. 2009;116(7):1257-63

3. Garway-Heath DF, Poinoosawmy D, Fitzke FW, Hitchings RA. Mapping the visual field to the optic disc in normal tension glaucoma eyes. Ophthalmology. 2000;107:
1809–1815

4. Hood DC, Raza AS, Method for comparing visual field defects to local RNFL and RGC damage seen on frequency domain OCT in patients with glaucoma.,Biomed Opt Express. 2011 Apr 5;2(5):1097-105