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Editors Selection IGR 9-1

Visual function: SITA versus FDT

Comment by Peter Shah on:

16842 Detecting visual function abnormalities using the Swedish interactive threshold algorithm and matrix perimetry in eyes with glaucomatous appearance of the optic disc, Sakata LM; Deleon-Ortega J; Arthur SN et al., Archives of Ophthalmology, 2007; 125: 340-345

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This observational case-control study by Sakata et al. (135) aimed to compare the ability of 24-2 frequency-doubling perimetry (FDP-Matrix) with standard automated perimetry with the Swedish interactive threshold algorithm (SAP-SITA) in the detection of visual function abnormalities in patients with 'glaucomatous-appearing' optic discs (GAOD). The FDP-Matrix is a second generation FDP that uses an increased number of test locations and smaller stimulus sizes, theoretically permitting a stimulus pattern that is equivalent to the Humphrey 24-2 field test. Eighty test subjects with GAOD were recruited from glaucoma clinics within the department, and compared with 54 control subjects. It is interesting to note that both test and control groups had an approximate ratio of white:African-American subjects of 50:50. GAOD were defined on the basis of masked observation of stereoscopic optic disc photographs. The methodology used to compare the two techniques was robust and statistical analysis of data was comprehensive.

Using the study criteria 40% of eyes with GAOD had normal visual function as assessed with both perimetry techniques, however, agreement between the two techniques was only moderate. No differences in sensitivity were found between the two techniques at the same level of specificity (89%) when any of the criteria that defined an abnormal visual field in the study were used.

The authors conclude  that the FDP-Matrix detected abnormal visual function in  more eyes with GAOD than did SAP-SITA, although this difference was not statistically significant. They conclude that each perimetric technique was identifying different sub-sets of eyes with GAOD as abnormal, and that the combination of techniques may therefore improve detection of visual function abnormalities in patients with glaucoma. Although this is a rigorous and well-conducted study, one is left with the feeling that there is insufficient clinical data presented on the patients with GAOD. For example, which of these subjects simply had anomalous (non-glaucomatous) optic discs, which had true pre-perimetric glaucoma, and which had true established glaucomatous optic neuropathy? Despite this reservation, the study adds to the literature on FDP and is an excellent source of information.

Comment by the Editor: Pre-perimetric glaucoma is an ambiguous term that does not convey well the plethora of clinical scenarios for detecting optic nerve injury. Glaucoma might be diagnosed in the presence of a disc (or RNFL) abnormality and a corresponding functional defect. A functional defect might be detected with a selective functional test (such as FDP or SWAP), and should not necessarily depend on the presence of a standard (white on white) perimetric defect. Glaucoma also can be diagnosed by detecting a progressive change in the optic disc, RNFL or visual field. In fact, this latter method for glaucoma diagnosis may be even more specific than the former.

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