Ординатура / Офтальмология / Английские материалы / Atlas of Glaucoma, Second Edition_Choplin, Lundy_2007

No change detection analyses currently are available for StratusOCT evaluation of optic disc topography or macular thickness.

line, allowing comparison of the RNFL profile over time (Figure 7.13).

Scanning laser polarimetry

The GDx VCC provides an ‘Advanced Serial Analysis’ report that displays a selection of up to four scans of the same eye chronologically, depicting the changes in RNFL with time (Figure 7.13). The report presents a Nerve Fiber Layer map, Deviation from Normal map, Difference from Baseline map, and TSNIT Parameter Table with trend analysis. The Deviation from Normal and Difference from Baseline maps are color coded to show probability of measurement compared to the normative database, and micrometer change from baseline, respectively. Additionally, a combination TSNIT graph shows the TSNIT RNFL thickness measurements at baseline and at each follow-up as a different-colored

Retinal thickness analysis

The Retinal Thickness Analyzer (RTA) system allows the clinician to generate ‘follow-up reports’ for both retinal thickness and optic disc topography. These reports are produced when a patient is scanned at least twice using the same analysis type. For optic disc topography, a cup/disc area map is shown for each consecutive scan, a deviation map illustrates areas of thickness deviation compared to the baseline thickness map, and stereometric parameters, with deviation from baseline values, are shown for each follow-up examination. Regression analysis results also are shown for all images, and changes in these results may signal glaucomatous progression (Figure 7.14).

SUMMARY OF RESULTS FOR

CHANGE DETECTION

Because glaucoma is a slowly progressing disease, and because the newest-generation imaging technologies described in this chapter have been in use for only a few years, no studies have yet reported the ability of HRT II, StratusOCT, GDx VCC, and RTA optic disc topography measurement to detect change over time.

One relevant study showed change over time in retinal height measurements in glaucomatous eyes using a previous version of the currently available confocal scanning laser ophthalmoscopy topographic change analysis software for the HRT. This study showed significant change in retinal height (i.e. tissue thinning) in 69% of 77 eyes followed for approximately 5 years. Significant change in visual function accompanied 27% of these eyes and tissue thinning was corroborated by assessment of stereoscopic optic disc photographs in 80% of those eyes for which stereophotographs were available.

CONCLUSIONS

Computer-based imaging techniques show considerable promise for detecting abnormalities in eyes with glaucoma. The fact that they provide objective, reproducible, quantitative measurements ondemand makes them clinically attractive. While the new-generation instruments discussed in this chapter have not been well tested for glaucoma detection, they appear to perform as well as, or better than, their predecessors. Although it is not recommended that clinical diagnoses be made based solely on measurements from these instruments, it appears obvious that the measurements obtained can supplement other available clinical information. However, clinicians need to be aware of the strengths and limitations of these techniques, including understanding the importance of good image quality, before utilizing imaging data for clinical decision-making. Finally, although these instruments appear promising for the detection of glaucomatous change over time, available scientific

data neither sufficiently support nor reject this claim. Further research is necessary to provide a

strong, evidence-based recommendation for their use in the monitoring of this disease.

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INTRODUCTION

The detection of nerve fiber loss and prevention of its development and progression is the ultimate goal of the ophthalmologist in the diagnosis and management of patients with glaucoma. At the present time, there is no proven reliable and consistent way to ‘count’ optic nerve fibers, compare the ‘count’ to known normals to determine the presence or absence of glaucomatous disease, and accurately determine whether the ‘count’ is changing over time. As axons are lost through the disease process, visual function declines in relation to the loss of fibers serving the region of the loss. Therefore, tests of optic nerve function are integral to the management of glaucoma patients as an indirect measure of the number of axons remaining.

Tests of optic nerve function can be objective or subjective. A variety of different test modalities have been investigated, looking for the ideal test that would be: (1) easy to administer; (2) mostly objective (requiring minimal decision-making or other efforts on the part of the patient); (3) highly sensitive to early loss or minimal change in the disease state; and (4) specific for glaucoma.

No objective test meeting these criteria has been found. Clinical functional testing for glaucoma consists mostly of ‘psychophysical’ tests, which by their very nature are highly subjective and susceptible to the shortcomings of human subjects. These tests require the patients to perceive something, intellectually interpret what was perceived,

remember the instructions regarding what is supposed to be said or done if the correct ‘something’ was perceived, and effect some type of verbal or motor response. Perception, memory, interpretation and action thus characterize such psychophysical tests, and can all (individually, collectively or in some combination) lead to variability in the results. This can sometimes lead to false conclusions regarding the state of the disease process and inappropriate treatment.

FUNCTIONAL TESTS IN GLAUCOMA

There is good evidence that chronic glaucoma selectively damages large optic nerve fibers, although fibers of all sizes are damaged. Functional testing, therefore, should be directed at the visual tasks subserved by these axons in an attempt to identify early damage (Table 8.1). Some investigators have shown associated functional changes attributable to the loss of large optic nerve fibers, including declines in contrast sensitivity at high spatial frequencies, loss of pattern-evoked electroretinographic responses (PERG) after death of ganglion cells, and attenuation of PERG responses for high temporal frequencies of stimulation, supporting the idea that some part of glaucoma damage involves loss of the function of these large-diameter nerve fibers. Other investigators have suggested that the PERG may be helpful in identifying patients with ocular hypertension who will develop signs of glaucoma.