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M. Fingeret, K. Martindale, A. Camp, E. Canellos; The Glaucoma Continuum: Does Loss on the Newer Perimetric Tests Precede Damage on Standard Automated Perimetry?. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1635. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The glaucoma continuum has been described as a process in which damage associated with the development of glaucoma is discovered in the optic nerve/retinal nerve fiber layer followed by loss on newer, more sensitive perimetric testing such as Frequency Doubling Technology perimetry (FDT), or Short- Wavelength Automated perimetry (SWAP). According to the continuum, Standard Automated Perimetry (SAP) is the last test in which glaucomatous damage occurs with the assumption that all patients with SAP loss also have damage on either SWAP or FDT. This study will examine individuals with early glaucomatous damage and compare results on three different perimetric tests.
27 individuals, 49 eyes (mean age 65.3+11.4 years old) with early primary open angle glaucoma (characteristic optic nerve damage and/or VF loss with mean deviation < 6 dB on HFA 24-2 SITA Standard perimetry) underwent visual field examinations. All individuals had a visual acuity of 20/40 or better and were free of any pathology that would result in visual field defects. Over a series of visits within 3 months time, 24-2 SITA Standard, 24-2 SITA SWAP, and 24-2 FDT Matrix Threshold perimetry were performed. All tests needed to be reliable. The number of significant points flagged at 2%, 1% and 0.5% levels was counted for each perimetric test and compared across tests.
The average number of significant points found on SAP was 3.20 (SD 3.57), SITA-SWAP 4.96 (SD 4.66), and FDT Matrix 4.08 (SD 4.57). In comparing the tests, only SAP and SITA SWAP (P=0.0364) demonstrated statistical significance in the number of points flagged. There was no significant difference between FDT Matrix and SITA SWAP or FDT Matrix and SAP in the number of points flagged. Of the 49 eyes, 12 had three points flagged on all visual field tests. There were two eyes that showed defects on SAP alone while 17 eyes showed defects on SWAP, FDT Threshold or both.
The glaucoma continuum appears to be a valid concept in regards to describing the process by which damage occurs. The majority of eyes (84%) demonstrated loss on at least one of the newer perimetric tests. Still, many individuals (49%) had loss on SAP as well but a higher percentage of visual field defects were picked up with the newer perimetric tests. One limitation of the study is that the specificity of the SITA strategies is by design similar while the normative data for the FDT Matrix was collected independently and specificity may not be the same. To truly confirm the concept of the glaucoma continuum it would be beneficial to conduct a longitudinal study involving individuals at risk for developing glaucoma.
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