Is There Still a Role for Stereo Disc Photography in the Diagnosis and Management of Glaucoma?
Paul J.
Mackenzie,
MD, PhD
George A.
Cioffi,
MD
With improvements in quantitative imaging technologies, such as Heidelberg Retinal Tomography (HRT) (Heidelberg Engineering, Heidelberg, Germany), optical coherence tomography (OCT), and scanning laser polarimetry (SLP) (ie, GDx [Carl Zeiss Meditec, Dublin, CA]), do we still need to obtain stereo disc photographs on glaucoma patients? Although these new imaging technologies provide important quantitative information about the state of the optic nerve head and the nerve fiber layer, these new data supplement rather than replace stereo disc photographs. Stereo disc photography, preferably with simultaneous acquisition, remains the standard of care for recording the appearance of the optic nerve head in glaucoma patients or suspects.
In practice, stereo disc photographs should be obtained on virtually all glaucoma patients and glaucoma suspects, especially at the time of the baseline examination, for several reasons. They provide a permanent record of the appearance of the optic nerve that does not depend on specialized viewing equipment. Photographic images more closely reproduce the actual appearance of the optic nerve as compared to any of the pseudo-color images provided by the quantitative imaging devices. Stereo disc photographs may also aid in making the initial diagnosis by enhancing the clinical examination. Photographs provide baseline documentation to which subsequent examinations can be compared for detection of change.
Unlike stereo disc photography, there is no guarantee that the new quantitative technologies will be forward compatible. Technology becomes obsolete at an ever increasing rate as newer and better instruments are built. Will the baseline image taken with today’s quantitative machine be compatible with a newer platform in the future? Even if the older images can be successfully imported into the new platform, will the critical features that are measured today still be relevant on the new platform and therefore useful for assessing progression? One study comparing the nerve fiber layer (NFL) thickness measurements between 2 versions of OCT found that even with a correction factor, the agreement between the 2 instruments was low.1 If different versions of the same instrument illustrate this problem, what will happen when entirely new technologies replace the existing ones? Stereo disc photographs can be obtained with the assurance that in 15 years the data encoded in these photographs will be accessible and still relevant for comparison.
Figure 6-1. Simultaneous stereo disc photograph captured using the Nidek 3-DX system. Superotemporal thinning and inferotemporal excavation are evident.
Diagnostic Accuracy
Photographs may improve the clinical examination by providing stereoscopic images that can be viewed under ideal conditions for extended periods of time, allowing for the discrimination of more subtle details. In the Ocular Hypertension Treatment Study (OHTS), review of stereo disc photos was more sensitive for detecting optic nerve hemorrhage than clinical examination. Only 16% of disc hemorrhages were detected on both clinical and photo review, whereas 84% were detected by review of stereo disc photos but missed on clinical examination.2
Although the new quantitative imaging technologies continue to improve with refinements in technology, in most studies they are not yet equal to the diagnostic accuracy achieved with stereo photography.3 Furthermore, the diagnostic utility may be overestimated since all of the quantitative methods perform more poorly in patients with milder glaucoma,4 yet most validation studies are usually performed on patients with confirmed glaucoma. Thus, the diagnostic accuracy of these quantitative tests may be overestimated for patients with mild, preperimetric glaucoma in which improved detection is most needed.5
Methods for Documenting Optic Nerve Head Appearance
There are several techniques for recording the appearance of the optic nerve head. The optic nerve appearance should be drawn during the clinical examination and may provide for meaningful comparison in some settings where other methods do not exist.6 In most studies, stereoscopic evaluation of photographs is more reliable than monoscopic evaluation, with larger estimates of cup-to-disc ratio under stereoscopic conditions.7 Stereo disc photography can be either sequential, in which photos are taken one after another from differing angles to simulate stereo separation, or simultaneous. In most studies, simultaneous stereo photographs have afforded the best stereoscopic effect (depth resolution) and the best reproducibility, likely due to the consistency of the focusing plane stereo angle.8
Stereo disc photographs can either be captured on color slide film or digitally with display on a high-quality computer monitor and some form of stereoscopic viewing device. There are several potential advantages to digital photography, including the ability to manipulate image output to enhance certain display features, the potential to rapidly alternate between different images at high magnification to assess progression, the ease of remotely sharing images, the ability to make multiple copies, and instant processing for immediate use during the patient’s visit. They can also be incorporated into electronic medical records.
Summary
Regardless of the method chosen, a photograph remains the best method for documenting the appearance of the optic nerve. Quantitative imaging methods show great promise for the diagnosis and management of glaucoma and as these technologies continue to improve, they will become more important in the care of glaucoma. But how long will it be before the appearance of the optic nerve is unimportant? Until then, stereo disc photography provides the best representation of the appearance of the disc and remains the most reliable archive to allow meaningful comparison over the long term.
References
1. Bourne RR, Medeiros FA, Bowd C, Jahanbakhsh K, Zangwill LM, Weinreb RN. Comparability of retinal nerve fiber layer thickness measurements of optical coherence tomography instruments. Invest Ophthalmol Vis Sci. 2005;46:1280-1285.
2. Budenz DL, Anderson DR, Feuer WJ, et al. Detection and prognostic significance of optic disc hemorrhages during the Ocular Hypertension Treatment Study. Ophthalmol. 2006;113:2137-2143.
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4. Medeiros FA, Zangwill LM, Bowd C, Sample PA, Weinreb RN. Influence of disease severity and optic disc size on the diagnostic performance of imaging instruments in glaucoma. Invest Ophthalmol Vis Sci. 2006;47:1008-1015.
5. Bowd C. Optical coherence tomography for clinical detection and monitoring of glaucoma? Br J Ophthalmol. 2007;91:853-854.
6. Shaffer RN, Ridgway WL, Brown R, Kramer SG. The use of diagrams to record changes in glaucomatous disks. Am J Ophthalmol. 1975;80;460-464.
7. Varma R, Steinmann WC, Scott IU. Expert agreement in evaluating the optic disc for glaucoma. Ophthalmology. 1992;99:215-221.
8. Rosenthal AR, Kottler MS, Donaldson DD, Falconer DG. Comparative reproducibility of the digital photogrammetric procedure utilizing three methods of stereophotography. Invest Ophthalmol Vis Sci. 1977;16:54-60.