A New Optokinetic Testing Method to Measure Rat Vision

Summary

The Optokinetic Nystagmus (OKN) behavioral testing method is used for the assessment of visual acuity in rodents. Here a simple method is demonstrated that can be easily set up in research laboratories for a reliable assessment of visual function in both normal and experimental rats.

Abstract

Optokinetic nystagmus (OKN) is a reflexive eye movement initiated by the motion of visual stimuli in the field of vision. The head-tracking movement associated with OKN is commonly used as a measure of visual function in rodents. To record OKN responses in normal and experimental rats, a simple and inexpensive apparatus has been developed. This setup uses two tablet screens to display the OKN visual stimulus consisting of high contrast black and white stripes generated using the OKN Stripes Visualization Web Application, a freely available software. The rat is placed inside a clear Plexiglass holder that limits movement so that the rat's head continuously faces the OKN display screen. The position of the rat holder can be changed to adjust the distance between the rat and the display screen. A micro-camera positioned above the rat holder is used to record the rat's visual activities. These recordings can be used for quantitative assessments. Based on the presence or absence of clear head-tracking, the OKN responses at different spatial frequencies can be determined. The collected data demonstrates a novel technique for reliable measurement of visual acuity in normal and retinal degenerate rats.

Introduction

When the eye is exposed to sustained full-field visual motion, a distinct pattern of fast and smooth tracking eye movements and low-acceleration head movements emerge in the direction of visual motion, called optokinetic nystagmus (OKN)^1,2. The neurological pathway of OKN passes from the retina to the lateral geniculate body, occipital lobe, and cerebellar flocculus and connects to the ocular motor neurons³. Neural damage anywhere along these neural pathways may lead to changes in the OKN responses. The OKN response is used as a tool to assess cerebral symmetry, psychogenic blindness, a....

Protocol

All animal procedures were performed in compliance with the experimental guidelines approved by the regional authorities and accepted by the Institutional Animal Care and Use Committee (IACUC) at the University of Southern California (USC), and conformed to the Association for Research in Vision and Ophthalmology (ARVO) Statement for the Use of Animals in Ophthalmic and Vision Research and the European directive 2010/63/EU on the protection of animals used for scientific purposes.

NOTE: The rats used in this study are pigmented retinal degenerate Royal College of Surgeons (RCS) rats and Long Evans (LE) rats. Figure 3

Results

The OKN testing was performed using retinal degenerate (RD) Royal College of Surgeons (RCS) rats and age-matched normal Long Evans (LE) rats. The LE rats (n = 4), were used for establishing the baseline data to determine visual acuity scores in normal rats using the new setup. Statistical analysis was carried out using Microsoft excel (mean ± standard deviation). LE rats exhibited robust head-tracking at spatial frequencies from 0.15 c/d to 0.33 c/d. To evaluate the reliability and effectiveness of the new OKN apparatus .......

Discussion

OKN is a reflexive saw tooth motion of the eyes in response to a drifting stimulus, which is used as a tool to assess visual acuity in human subjects³. In animals, including primates and rodents, OKN testing is used as a quantitative measurement of visual function. The present study describes a novel, inexpensive OKN apparatus that can be easily set up in research laboratories for OKN behavioral testing in rats. OKN assessments in rodents were performed by different approaches. Previously, an inte.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
iPad Mini	Apple	A1489	Two iPad Minis are used to display the OKN Stripes Visualization Software.
Micro-camera/Micro-Camera Attachment	Lanon	B097H6WWDS	The micro-camera is used to record the experiment. The micro-camera attachment connects to the desk and holds the camera facing the rat. The head tracking responses are recorded and assessed at varying distances, spatial frequencies, and directions.
Plexiglass Tube/Rat Holder	Best Acrylics	B07KMF31MC	The Plexiglass Tube is used to restrain the rat, with their head exposed, for the duration of the experiment. The tube is attached to another vertical plexiglass tube attachment to stabilize the rat holder during the experiment. The entire apparatus was designed and constructed in the lab.
Plexiglass Tube Attachment	Best Acrylics	B07KMF31MC	This attachment holds the rat holder in front of the iPad screens, and allows the distance between the rat and iPads to be manipulated.
Screen Holders	Kabcon	B08JLRPKQ1	Two screen holders are used to hold the iPads up in order to display the OKN Stripes Visualization Software to the rat.
OKN Stripes Visualization Web Application	The MIT License (MIT) Copyright (c) 2016 Anton Yakushin	https://antonyakushin.github.io/okn-stripes-visualization/	This application is a freely available softeware to display visual stimuli (black and white stripes) at different frequencies