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Editors Selection IGR 9-2
Examination methods: Laser scanning: FDT versus OCT
Comment by Jose-Maria Martinez de la Casa on:
18113 Retinal nerve fiber layer damage as assessed by optical coherence tomography in eyes with a visual field defect detected by frequency doubling technology perimetry but not by standard automated perimetry, Kim TW; Zangwill LM; Bowd C et al., Ophthalmology, 2007; 114: 1053-1057
The Frequency Doubling Technology perimetry (FDT) targets a specific subpopulation of retinal ganglion cells and several studies have suggested it could serve to detect glaucomatous damage before the appearance of the first defects observed using conventional perimetry (standard automated perimetry, SAP).
In this observational case-control study,Kim et al. (570) tried to correlate defects detected using FDT with structural defects in the retinal nerve fibre layer as determined through optimal coherence tomography (OCT). They examined 93 patients assigned to four groups according to their SAP and FDT results.
A certain correlation between the functional alterations detected by FDT and the structural changes detected by OCT are shown in patients with a normal SAPTheir findings indicate that in patients with a normal SAP and abnormal FDT result, retinal nerve fibre thickness was significantly reduced in the 4 and 5 o'clock hour sectors than in the normal SAP/normal FDT group. When they examined the number of patients with any yellow-coloured sector (p < 5% of being normal) they noted significant differences in
the 5 o'clock sector and in the inferior and superior quadrants. When they examined the number of quadrants coloured red (p < 1% of being normal) they only found differences at the level of the lower quadrant.
The study's conclusion is therefore that there is certain correlation between the functional alterations detected by FDT and the structural changes detected by OCT in patients showing a normal SAP. As already demonstrated by others, structural changes are initially most evident in the superior and inferior quadrants of the retinal nerve fibre layer. Future studies should provide information on whether such structural changes translate to subsequent conventional perimetry defects.
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