Abstract

Volume.123 Number.3

Physiology of Vision and Clinical Practice in Ophthalmology
Masayuki Horiguchi
Department of Ophthalmoloy, Fujita Health University School of Medicine

Ocular physiology is extremely important for understanding clinical ophthalmology. For many years, we have been researching on how the retina takes in light and converts it into visual images and on how the visual center analyzes that information. Furthermore, in clinical practice, we have been considering physiological approaches for surgery and diagnosis based on such knowledge. Here we will introduce the results of our research thus far.
I. Basic electrophysiology
1. Recording retinal intracellular potentials
The method of recording the potential of individual cells by inserting microelectrodes into retinal cells has been a major driving force for advancements in retinal physiology. We used the retina of Xenopus laevis to record the potential of horizontal cells and demonstrated how rods inhibit cones via horizontal cells in the dark. The silent substitution method was introduced to retinal electrophysiology in this study, thereby contributing greatly to later research in electrophysiology.
2. Patch clamping on retinal neurons
Microelectrodes are sealed onto the cell membrane, and not inside the retinal cell, to record channels on the membrane. We used patch clamping on fragments of the retina obtained during vitreous surgery, such as that for retinal detachment, and discovered that human rods and bipolar cells have sodium channels and that rods generate spikes when strong light stimuli are off.
II. Clinical electrophysiology
We have conducted many studies. The effects of the recently developed inverted internal limiting membrane (ILM) flap technique on the retina and the effects of vitreous surgery on electroretinography will be introduced.
III. Clinical psychophysics
1. Visual test of the macular hole
Macular holes are circular holes formed by foveal dehiscence of the retina; thus, the fixation point is unstable. We devised a method of testing visual acuity by presenting many Landolt rings, and successfully measured visual acuity around the macular hole.
2. Migration of the macular hole visual cells
The Watzke-Allen test consists of observing distortions due to migration of visual cells by the hole with a slit beam. The slit beam is enlarged gradually to seek the threshold value to measure the range of visual cell migration. The result of this test showed that horizontal and vertical migrations were different in the holes of ≥ 80%, indicating, along with results of optical coherence tomography, that many macular holes were not perfect circles.
3. Image distortion of the epimacular membrane
Image distortion and macropsia of the epimacular membrane have been previously studied using the Amsler's chart, M-CHARTS, and the new aniseikonia test. In a study, the authors found many patients with bilateral image distortion despite having an epimacular membrane in only one eye, which suggested, with high likelihood, that the visual center is involved in the image distortion.
IV. Clinical ophthalmology (surgery and diagnosis)
1. Intraocular surgery using tissue staining
Intraocular surgery requires the visualization of transparent tissues; thus, only improvements in microscope lighting are not always sufficient. We devised a method to use indocyanine green to improve visibility by staining the cranial sac for dissection in mature cataract surgery. It was the first time that a method of tissue staining was reported in ophthalmology, and this technique has since been applied to many other intraocular surgeries.
2. Optical fiber-free intravitreal surgery system (OFFISS) and wide-angle view system
We also developed a method of performing vitreous surgery under microscope lighting and the wide-angle view system that uses this system. Many wide-angle view systems used today are based on this principle.
3. Wide-angle ultrasonography test
Unlike magnetic resonance imaging (MRI), it is impossible to obtain an image of the entire eyeball using the standard B-mode for ophthalmology. Therefore, we invented a device that enables imaging of the entire eyeball. It is difficult to use MRI for cross-sectional analysis of the eyeballs of patients. The wide-angle ultrasonography test can be used to study the relationships between eyeball shape and ocular diseases.
Nippon Ganka Gakkai Zasshi (J Jpn Ophthalmol Soc) 123: 226-259, 2019.

Key words
Visual physiology, Macular hole, Epimacular membrane, Microscopic surgery, Echogram
Reprint requests to
Masayuki Horiguchi, M.D., Ph.D. Department of Ophthalmology, Fujita Health University School of Medicine. 1-98 Dengakugakubo, Kutsukake-cho, Toyoake-shi, Aichi-ken 470-1192, Japan