ABSTRACT Background: Achromatic automated perimetry (AAP) is limited in its ability to detect very early visual field loss in ocular hypertensive patients.Tests targeting axons that are selectively damaged, or have low redundancy, may detect visual field losses before they are seen on AAP . It has been claimed that short wavelength automated perimetry (SWAP) and frequency doubling perimetry (FDP) are two tests that provide early detection. Methods: Patients (n = 62) were selected on the basis that they had raised intraocular pressure but normal visual fields detected by AAP . A SWAP and an FDP was performed on each of the patients and the results compared. Fields were scored as either normal or abnormal based on criteria used in previous studies. Results: On comparing FDP with SWAP as the ‘gold stan- dard’, a sensitivity of 88.9% and a specificity of 96.2% was found, showing a high concordance between the two tests. Conclusion: These results suggest that as SWAP may be predictive of AAP visual field loss, FDP may be similarly predictive. Key words: frequency doubling, ocular hypertension, perimetry, short wavelength, visual fields. INTRODUCTION Since its introduction in the late 1970s, 1 achromatic auto- mated perimetry (AAP) has become the ‘gold standard’ for the detection of visual field loss. This situation resulted from the reproducibility and accuracy of the technique, 2–5 and greater sensitivity for small scotomas, compared with manual quantitative kinetic perimetry. 2,4,5 However, for all its advantages, AAP detects damage relatively late; by the time damage has been detected, up to 50% of the retinal ganglion cell axons in the damaged area may have been lost. 6,7 A method to detect visual field loss earlier is there- fore required. 8 In 1995, Johnson outlined concepts for formulating such a method. 9 First was the ‘selective loss theory’, which had the aim of isolating optic nerve fibres that were most sus- ceptible to early glaucomatous damage. At high intraocular pressure (IOP), larger axons may be lost in greater numbers relative to the entire population, resulting in a decreasing mean axonal diameter as glaucoma progresses. 8,10–12 Perhaps larger axons do not withstand external compressive forces as well, or tolerate ischaemia poorly (possibly owing to their smaller surface to volume ratio). 8,11 This loss may also be a consequence of the relatively high proportions of larger axons that pass through the vertical poles of the optic nerve head. Because the pores in the lamina cribrosa are larger and the supportive collagenous sheets are thinner at these points, the contained axons may be more susceptible to damage from raised IOP. 6,10,11,13–15 Second, Johnson postulated a ‘reduced redundancy theory’, such that the loss of sparsely represented ganglion cell populations (therefore with minimal overlap or redun- dancy for their receptive fields) is more likely to lead to an earlier functional deficit. 9 The magnocellular (M) pathway consists of large axons, that have large receptive fields and are sparsely represented (approximately 15% of all retinal ganglion cells). 8,16,17 Approximately 15% of these pathways exhibit non-linear (Y-type) characteristics (or My characteristics). 17–19 Because frequency doubling perimetry (FDP) may test this phen- omenon selectively, 9,20 FDP could detect damage before detection by AAP is possible. 21,22 This argument can also be applied to axons of the konio- cellular pathway, which project from Blue-On cells. 23,24 Lying between the magnocellular and parvocellular layers of the lateral geniculate nucleus, 24 these axons are relatively few in number, are about 50% larger than green or red Clinical and Experimental Ophthalmology (2000) 28, 248–252 Original Article A comparison of short wavelength automated perimetry with frequency doubling perimetry for the early detection of visual field loss in ocular hypertension John Landers MB BS, 1 Ivan Goldberg FRACO 1 and Stuart Graham FRACO 1,2 1 Eye Associates, Park House and 2 Save Sight Institute, Sydney University, Sydney, New South Wales, Australia ■ Correspondence: Dr J Landers, Park House, Floor 4, Suite 2, 187 Macquarie Street, Sydney, NSW 2000, Australia. Email: rauaroha@raco.org.au