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Arch Ophthalmol. 2004;122:1540-1543.

Frequency-doubling technology (FDT) has been useful in screening patients for glaucoma.¹ One report shows that 1 drop of unoprostone could induce improvement with FDT by lowering intraocular pressure and increasing ocular blood flow.² We examined 1 patient with secondary glaucoma and transient rise of high intraocular pressure with FDT and with a Humphrey field analyzer (HFA) (Carl Zeiss Meditec, Inc, Dublin, Calif) for 1 year to study the effect of intraocular pressure on visual field results.

Report of a Case
A 33-year-old woman had had attacks of high intraocular pressure with slight inflammation several times in both eyes. Her visual acuity was 20/16.7 OU. Fluorescein angiography showed no abnormal findings. With maximally tolerated therapy, intraocular pressure remained higher than 40 mm Hg OS, and the patient underwent trabeculectomy in that eye. Her left intraocular pressure stayed in the 20s after surgery. Her right intraocular pressure transiently rose to higher than 40 mm Hg with maximally tolerated therapy. The high pressure decreased to normal levels within 1 month. The patient had large disc cupping in the right eye; a 0.472 cup-disc ratio was determined using a retina tomograph (Heidelberg Engineering, Heidelberg, Germany). The HFA visual fields were always normal independent of intraocular pressure for 1 year (Figure 1) (Table1) . The FDT, however, showed abnormal areas only twice during the same period, with high intraocular pressure (> 40 mm Hg) (Figure 2). On the same day in February 2002, when intraocular pressure was 45 mm Hg, the FDT showed abnormal findings while the HFA appeared normal. During the final attack, 1% apraclonidine reduced intraocular pressure transiently and improved the FDT mean deviation slightly in 1 hour (Figure 2 ). The FDT mean deviation correlated well with changes in the intraocular pressure, but not necessarily with the FDT pattern standard deviation (Table 1). No inflammatory cells were seen in the anterior chamber of the right eye and no corneal edema was observed during the attacks.

View larger version (108K): [in this window] [in a new window] Figure 1. The Humphrey field analyzer always showed normal visual field findings independent of intraocular pressure at examination. MD indicates mean deviation; PSD, pattern standard deviation; CSPD, corrected pattern standard deviation.

View this table: [in this window] [in a new window] Visual Field Indexes in Relation to Intraocular Pressure

View larger version (87K): [in this window] [in a new window] Figure 2. The frequency-doubling technology (FDT) showed abnormal areas only with high intraocular pressure (> 40 mm Hg) twice and normal visual fields with normal intraocular pressure 6 times. In April 2003, 1% apraclonidine eyedrops decreased intraocular pressure (from 39 to 27 mm Hg) and improved mean deviation (MD) with FDT under the same-sized pupil (6 mm). PSD indicates pattern standard deviation.

Comment
In this patient, visual field defects detected with FDT were thought to be due to elevated intraocular pressure. After reduction of intraocular pressure, the FDT mean deviation always showed improvement, even in 1 hour. Visual field loss with FDT under high intraocular pressure was reversible. The mechanism for this improvement was unclear. The FDT was thought to reflect the function of relatively large retinal ganglion cells, called the M ganglion cells, since the FDT has large-sized (10°), high-temporal-frequency (25 Hz) and low-spatial-frequency (0.25 candela/s) stimuli, inducing frequency-doubling illusion.³ The large retinal ganglion cells that may not be completely damaged under elevated intraocular pressure could recover when intraocular pressure was lowered. Another mechanism was improvement in corneal edema.⁴ No epithelial edema was seen by slitlamp microscopy. Not only did diffuse loss mean deviation appear, but abnormal areas appeared with high intraocular pressure in the present patient. If corneal edema affected visual field, only diffuse loss would occur. Refractive error was corrected at examination of FDT. Good visual acuity was maintained under high intraocular pressure. In conclusion, FDT perimetry may show intraocular pressure–dependent, reversible changes.

The authors have no relevant financial interest in this article.

AUTHOR INFORMATION

Naoya Fujimoto, MD; Dawei Zhang, MD; Eiju Sato, MD; Osamu Miyauchi, MD; Atsushi Mizota, MD

Correspondence: Dr Fujimoto, 1-8-1 Inohana, Chuoku, Chiba 260-8670, Japan, Department of Ophthalmology and Visual Science, Graduate School of Medicine, Chiba University (fujimoto{at}faculty.chiba-u.jp).

REFERENCES
1. Johnson CA, Samuels SJ. Screening for glaucomatous visual field loss with frequency-doubling perimetry. Invest Ophthalmol Vis Sci. 1997;38:413-425. FREE FULL TEXT 2. Sponsel WE, Paris G, Trigo Y, Pena M. Comparative effects of latanoprost (Xalatan) and unoprostone (Rescula) in patients with open-angle glaucoma and suspected glaucoma. Am J Ophthalmol. 2002;134:552-559. FULL TEXT | ISI | PUBMED 3. Kelly DH. Frequency doubling in visual responses. J Opt Soc Am. 1966;56:1628-1633. 4. Ytteborg J, Dohlman CH. Corneal edema and intraocular pressure: II. Clinical results. Arch Ophthalmol. 1965;74:477-484.

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