Detection of early glaucoma with FDT and SWAP : the results of a longitudinal study

Purpose: To evaluate the ability of Frequency–Doubling Technology (FDT) perimetry and short wavelength automated perimetry (SWAP) in detecting the presence of early glaucoma. Methods: Twenty–three patients with glaucomatous optic nerve head, retinal nerve fiber layer (RNFL) defects, but normal standard automated perimetry (SAP) were included in the study. Each patient underwent 3 tests with FDT (program N–30 full threshold) and 3 with SWAP (full threshold 30–II) in a randomized sequence. Only the last examination with each technique was included in the analysis. Patients were then followed and, after 5 years, were retested with the same procedures. SAP was considered normal if MD, CPSD and GHT were all normal. Criteria for abnormality of FDT and of SWAP included the presence of at least 2 abnormal contiguous points (p < 5%) corresponding to the RNFL defects, and an abnormal GHT and the presence of at least 3 abnormal contiguous points (p< 5%) corresponding to the RNFL defects respectively. Results: At study inclusion, 16/23 (70%) had an abormal FDT and 6/23 patients (26%) had an abnormal SWAP. After 5 years, 12/23 (52%) developed a glaucomatous visual field defect at SAP. All these 12 patients presented an abnormal FDT and an abnormal SWAP at the 5 years’ evaluation. In 11/12 (92%) cases, FDT was abnormal at inclusion, while only 5/12 (42%) patients had an abnormal SWAP at inclusion (p = 0.05). Conclusions: Defects at both FDT and SWAP might preceed the onset of SAP changes in early glaucoma. FDT might detect progression of glaucoma earlier than SWAP.