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Frequency doubling technology (FDT, Humphrey-Zeiss and Welch Allyn, Dublin, CA, USA) has been developed to screen for glaucoma.1 FDT could detect abnormalities in patients with full visual fields tested by Humphrey field analyser (HFA, Humphrey-Zeiss, Dublin, CA, USA) and nerve fibre layer defects2 or normal visual fields and large disc cupping.3 Inversely, FDT did not always detect visual field loss in patients with glaucomatous visual field defects determined by HFA (Fig 1), but it was rare.4,5 That was because the ability of FDT to detect glaucomatous visual field loss was limited or for some other reasons. In this study, we presumed that patients with severe damage in one eye had relative hypersensitivity in another eye.
Twenty nine patients (23 men and six women) had one normal healthy eye and one severely damaged eye. Their ages ranged from 18–69 years (mean 51 years). Patients had been examined with threshold c-20 of FDT version 2.6 once. A normal healthy eye meant normal vision (20/20 or better), normal intraocular pressure (less than 21 mm Hg on two occasions), no inflammation, and normal fundus observed clinically. The damaged eye had poor vision (20/200 or worse) or severe visual field defects (mean deviation with FDT less than −6.0 dB). Damage was variously the result of optic nerve lesion by angle recession glaucoma, uveitic glaucoma, or tumour at the orbital apex. Primary open angle glaucoma, optic neuritis or tumour in the brain were excluded, since such conditions usually involve both eyes. As controls, 26 (20 men and six women) normal healthy volunteers were recruited for this study. Their ages ranged from 23 to 70 years (mean 51 years). Patients had been examined with threshold c-20 of FDT version 2.6 once. They had normal vision (20/20 or better), normal intraocular pressure (less than 21 mm Hg), and normal fundus findings. All subjects were examined with threshold c-20 of FDT version 2.6. Mean sensitivity was calculated from all 17 test areas. Mean sensitivity with one normal healthy eye and one severe damaged eye was compared to that in subjects with two normal healthy eyes with Mann-Whitney U test. All results of less than 20% of fixation loss, 20% of false positive, and 33% of false negative were adopted. The research followed institutional guidelines and the tenets of the World Medical Association Declaration of Helsinki. We obtained written informed consent from all patients before their entry in this study.
Eighty results of 55 patients were studied for analysis. One result in patients with two healthy eyes was excluded because of an unreliable result. Twenty nine eyes with severe damage in one eye had a significantly higher mean sensitivity (mean 30.8 (SE 0.47) dB) in one healthy eye than did both normal healthy eyes (p=0.0065, 28.8 (0.50) dB in 26 better eyes and p=0.0005, 27.9 (0.56) dB in 25 worse eyes) (Fig 2).
It was interesting that there were 2 dB differences in sensitivity between patients with a normal healthy eye. The reason for eyes with severe damage in one eye having relative hypersensitivity was unclear. One possible explanation was because the pathway detected by FDT is thought to be a magnocellular pathway and a relatively less, complemental mechanism might work in magnocellular pathway.
In conclusion, patients with one severely damaged eye had relative hypersensitivity in one healthy eye. Estimation of such patients should be considered carefully.
Supported in part by a grant in aid for scientific research (Dr Fujimoto No 13671822 and Dr Hanawa No 14770942), from Ministry of Education, Culture, Sports, Science and Technology, Japan.