Comparison of SWAP and SAP on the point of glaucoma conversion

Ioannis Havvas,^1,2 Dimitris Papaconstantinou,¹ Marilita M Moschos,¹ Panagiotis G Theodossiadis,¹ Vasilios Andreanos,¹ Pantelis Ekatomatis,¹ Ioannis Vergados,¹ Dimitrios Andreanos<sup>1

1</sup>Department of Ophthalmology, School of Medicine, University of Athens, General Hospital of Athens, Athens, ²Department of Ophthalmology, General Hospital of Patras, Patras, Greece

Background: The purpose of this study was to compare the two perimetric modalities, SWAP (short wavelength automated perimetry) and SAP (standard automated perimetry), on the point of conversion to glaucoma.
Methods: In this prospective, longitudinal, follow-up study, 282 patients with ocular hypertension were recruited consecutively and tested with both SAP and SWAP annually for 5 years or until the onset of conversion to glaucoma. SAP and SWAP perimetry was performed with the Humphrey Field Analyzer II using the 24-2 full-threshold test. Abnormality for both SAP and SWAP fields was determined on the pattern deviation plot and defined as either a) one point below the 0.5% probability level or b) a cluster of 2 or more points below 1% or c) a cluster of 3 or more points below 2% or d) a cluster of 4 or more points below 5%. Abnormal tests had to be confirmed on a subsequent test within one year to be classified as conversion.
Results: Of the 282 patients initially recruited, 32 were excluded. Of the 250 remaining patients, a total of 38 converted during the follow-up period; 36.8% of conversions were detected earlier with SWAP, 29% simultaneously, and 34.2% were not detected with SWAP during the follow-up period; 2.4% of patients showed SWAP visual field loss that did not result in conversion during the follow-up period.
Conclusion: The results in our study are inconclusive. There were patients with earlier, simultaneous, or no SWAP conversion, with SAP conversion as the golden standard criterion. One should consider both SAP and SWAP with confirmation when visual field loss is evident to maximize early detection of glaucoma, because it appears that each method identifies early glaucoma in a subset of patients and these subsets overlap only partially.

Keywords: short wavelength automated perimetry, standard automated perimetry, blue on yellow, glaucoma conversion, ocular hypertension