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OCT detects glaucomatous damage up to 8 years before visual field
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Researchers were able to assess the thickness of the retinal nerve fiber layer utilizing optical coherence tomography to detect glaucoma before the appearance of visual field defects, according to a study recently published in Ophthalmology.
Kuang and colleagues conducted an observational cohort study to evaluate the diagnostic accuracy of retinal nerve fiber layer (RNFL) thickness measurements from OCT as well as gained lead time.
The study consisted of 75 eyes of 75 patients suspected of having glaucoma and 75 eyes of 75 healthy subjects. Researchers analyzed RNFL thickness measurements, which were taken when the earliest standard automated perimetry (SAP) defect was detected and yearly before field loss development.
Results showed that when visual field defects were detected, average RNFL thickness was 90.6±8.0 μm in healthy eyes and 75.0±9.8 μm in glaucomatous eyes. Researchers noted that significant differences in RNFL thickness were discovered up to 8 years before the presence of visual field defects.
"For example, at 95% specificity cutoff, up to 44% of subjects had abnormal average RNFL thickness at 2 years before development of a field defect," they stated. "This number reduced to 35% at 4 years and to 19% at 8 years. Although 19% may be seen as an apparently small proportion, it is important to consider that 8 years is a relatively large amount of time, and such lead time could have significant management implications to a significant group of patients."
The authors concluded: "Assessment of RNFL thickness with OCT was able to detect glaucomatous damage before the appearance of visual field defects on SAP. In many subjects, significantly long lead times would be gained when applying OCT as an ancillary diagnostic tool. Future research should evaluate the implications of OCT-assisted decision making in preventing functional impairment and disability in glaucoma." – by Chelsea Frajerman Pardes
Disclosure: Kuang reported no relevant financial disclosures. Please see the full study for a list of all other authors' relevant financial disclosures.
Perspective
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Derek MacDonald, OD, FAAO
“What's past is prologue,” (Shakespeare W).
“We need to strive for better detection and follow-up of glaucoma damage to prevent needless blindness” (Quigley).
“… the vast majority of subjects with glaucomatous visual field defects already had demonstrable nerve fiber layer (NFL) abnormalities … at least 3 to 5 years before the onset of field loss. Quantifying the actual thickness of the NFL ... offers greater promise” (Sommer).
Some 25 years later, Kuang and colleagues have demonstrated that significant loss of the RNFL was detected by optical coherence tomography several years before the development of visual field loss. In doing so, they support OCT as a targeted ancillary diagnostic tool that provides valuable additional information for patients already considered to be glaucoma suspects, some who may, in fact, have pre-perimetric disease.
The authors wisely remind us that longitudinal evaluation of structure and function are complementary, not interchangeable. They also warn us that the RNFL “tipping point” at which visual field abnormalities were first detected may fall within the normal range of many instruments. Indeed, green is not always good.
When leveraged intelligently, OCT may enable earlier detection of disease presence and progression, inform our decision-making around treatment and monitoring, and ultimately improve the outcomes, and the lives, of our patients.
References:
Shakespeare W. The Tempest. circa 1610.
Quigley HA. Surv Ophthalmol. 1985;30(2):111, 117-1126.
Sommer A, et al. Arch Ophthalmol. 1991;109(1):77-83.
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