Advance Publication
The Journal of Veterinary Medical Science Accepted Date: 4 Nov 2015 J-STAGE Advance Published Date: 8 Dec 2015
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Internal Medicine
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note
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TITLE
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Effect of refractive error on visual evoked potentials with pattern
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stimulation in dogs
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Yosuke Ito 1 ) , Seiya Maehara 1 ) , Yoshiki Itoh 2) , Ai Matsui 1 ) , Miri Hayashi 1 ) ,
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Akira Kubo 1 ) and Tsuyoshi Uchide 1 )
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1)
Department of Small Animal Clinical Sciences, School of Veterinary
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Medicine, Rakuno Gakuen University, 582 Bunkyodai -Midorimachi,
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Ebetsu, Hokkaido 069-8501, Japan
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2) Department of Veterinary Radiology, Joint Fac ulty of Veterinary
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Medicine, Yamaguchi University, 1677-1 Yoshida, Yamaguchi,
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Yamaguchi 753-8515, Japan
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Corresponding author: Seiya MAEHARA
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Tel: +81 11-388-4853; Fax: +81 11-388-4853
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E-mail address:
[email protected] (Seiya Maehara)
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Running head: EFFECT OF REFRACTIVE ERROR ON P-VEP IN DOGS
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Abstract
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The purpose of this study was to investigate the effects of refractive error
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on canine visual evoked potentials with pattern stimulation (P -VEP). Six
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normal beagle dogs were used. The refractive power of the recorded eyes
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was measured by skiascopy. The refractive power was corrected to -4
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diopters (D) to +2 D using contact lens . P-VEP was recorded at each
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refractive power. The stimulus pattern size and distance were 50.3 arc-min
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and 50 cm. The P100 appeared at almost 100 msec at -2 D (at which the
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stimulus monitor was in focus). There was significant prolongation of the
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P100 implicit time at -4, -3, 0 and +1 D compared with -2 D, respectively.
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We concluded that the refractive power of the eye affected the P100
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implicit time in canine P-VEP recording.
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Key words
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dog, pattern stimulated visual evoked potentials , P100 implicit time,
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refractive power
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The visual evoked potential (VEP) test is a method for detecting the
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brain wave signal s from the visual cortex induced by a light stimulus. VEP
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is affected by the function of all regions in the visual pathway and classified
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into
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checkerboard pattern stimulus and flash -stimulated VEP (F -VEP) with a
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flash stimulus. In human medicine, the F-VEP test is useful when a subject
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has poor vision and/or cooperates poorly (e.g., infants, children ). The P-VEP
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is used to support the diagnosis of a nervous abnormality (e.g., optic neuritis,
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multiple sclerosis ) or a psychogenic visual disturbance or malingering [10,
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14]. However, cooperation of the subject is necessary to perform the P -VEP
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test. Moreover, the P-VEP test is applied as a visual acuity test [7, 11, 15].
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In the veterinary medical science, the VEP test is used to evaluate
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development and neurologic disorders of visual function in postnatal
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animals
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toxicological tests [12]. There are some reports indicating that the VEP test
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may be useful for evaluation of the visual pathway clinically, as in the case
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of human medicine. There were some reports indicating a relation between
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the P-VEP and stimulus pattern size or depth of anesthesia [5, 6]. However,
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there
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consideration of refractive power ; on the other hand , no studies have
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performed transient P-VEP.
pattern-stimulated
and
are
VEP
to investigate
few
studies
that
(P -VEP)
toxic effects
have
with
on
performed
a
contrast -reversing
the visual pathway
steady-state
P-VEP
in
in
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In this study, we recorded P -VEP with a constant stimulus pat tern
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size and stimulus distance and with changing refractive power of the eye to
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investigate the effects of refractive error of the eye on P-VEP.
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Six eyes from six clinically normal beagle dogs (four male and two
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female) were used in this study. The dogs were 4 to 6 years of age (mean:
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5.8 years) and weighed 10.7 to 14.5 kg (mean: 13.9 kg). They had no
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abnormalities in neurologic and ophthalmic examinations before the study.
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Examinations included pupillary light reflex, menace response, applanation
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tonometry (Tono-Pen XL, Medtronic Solan, Jacksonville, FL, U.S.A.), slit-
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lamp biomicroscopy (SL-7, Kowa, Aichi, Japan), ophthalmoscopy (TRC-50IX,
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TOPCON, Tokyo, Japan ) and electroretinography (LE-3000, Tomey, Aichi,
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Japan). This study was conducted according to the g uidelines of the
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Experimental Animal Research Committee of Rakuno Gakuen University.
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The refractive power of the recorded eyes was measured by
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skiascopy according to the previous method reported by Maehara et al. [8].
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The refractive power was measured with a streak retinoscope ( Streak
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Retinoscope RX-3A, Neits Instruments Co., Ltd., Tokyo, Japan) and a
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skiascopic lens (Hatake Skiascope, Handaya Co., Ltd., Tokyo, Japan) under
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dim light 60 minutes after applying cyclopentolate hydrochloride eye dr ops
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(Cyplegin 1%, Santen Pharmaceutical Co., Ltd., Osaka, Japan) as a
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cycloplegic drug. The measurement distance was set as 50 cm. The refractive
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power of the eyes was corrected to -4 diopters (D), -3 D, -2 D, -1 D, 0 D, +1
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D and +2 D using soft contact lenses (SCLs; PremiO, Menicon Co., Ltd.,
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Aichi, Japan) after obtaining the results of the skiascopy. The refractive
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power of the subject’s eye was re measured by skiascopy to confirm that the
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refractive power was corrected. For P-VEP recording, needle elect rodes
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(VEP needle electrodes, Mayo Corporation , Nagoya, Japan) were positioned
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at the inion (external occipital protuberance) as the recording electrode and
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the nasion (nasal point) as the reference electrode. A plate -type electrode
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(LE ear electrode, Mayo Corporation) was positioned on the inner surface of
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the right auricle as an earth electrode , as in previous reports [5, 6] . Prior
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to recording, all dogs were sedated with a combination of 0.01 mg/kg
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medetomidine
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midazolam (Dormicam, Astellas Pharma, Tokyo, Japan) and 0.025 mg/kg
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butorphanol (Vetorphale, Meiji Seika Pharma) injected intravenously. P-
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VEP was recorded with a portable VEP system (LE -3000, Tomey) and
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pattern stimulus display (PS-410, Tomey). The details of this display were
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as follows: indicated color, yellow (580 nm); resolution, 640 × 400 dots;
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indicated area, 122 × 195 mm; pixel size, 0.22 × 0.22 mm; frame frequency,
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60 Hz; contrast, 75%, mean luminosity, 15 cd/m 2 . The testing distance,
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which was the distance from the cornea to the display, was 50 cm, the
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stimulus pattern size was 7.31 mm, and the visual angle was 50.3 arc -min
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at -2 D, which represented perfect focus. This visual angle was adopted
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based on a previous study [6]. The stimulation rate was 3 reversals/sec. The
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P-VEP signal was averaged from 64 repetitions. P-VEP was recorded under
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dim lighting. An eye speculum (BARRAQUER Speculum, Inami & Co., Ltd.,
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Tokyo, Japan) was used to keep the eyelids open , and physiological saline
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eye drops were instilled for corneal hydration. The subject’s eye was
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supported with a 6–0 silk thread (6-0 Silk, MANI, Tochigi, Japan) through
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the dorsal bulbar conjunctiva to gaze at the pattern stimulus display. The
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unrecorded eye was occluded with a bandage to avoid stimulation.
(Domitor,
ZENOAQ,
Fukushima,
Japan),
0.15
mg/kg
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In P-VEP recording in humans, the largest negative peak appear s at
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almost 75 msec and is referred to as the N75 after stimulation , and the
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largest positive peak appears at almost 100 msec and is referred to as the
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P100 [2]. In this study, P100 implicit time and N75 -P100 amplitude were
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estimated according to a standard determined by the International Society
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for Clinical Electrophysiology of Vision ( ISCEV) [13]. In each dog, P-VEP
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recording was performed three times, and the mean was calculated from the
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data of the individual. The P100 implicit times and N75 -P100 amplitudes
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obtained at -2 D were compared with The P100 implicit times and N75 -P100
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amplitudes obtained at all other test refractive power s by paired t-test. The
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statistical significance of differences was determined with P
