- Email: [email protected]
The Tools of Visual Testing
866
AMERICAN JOURNAL OF OPHTHALMOLOGY
not mean that there is a large "saccadic dead zone" of radius 17-30 min of arc; rather some of the responses are drifts, or se quences of tiny saccades that can only be detected by contact lens techniques. "Sac cadic suppression" is not necessarily a marked effect and saccades are not based simply on the retinal position of the tar get—-the eye responds to cues delivered dur ing saccades (dark-adapted eye, no back ground) and makes allowance for any other saccadic movement that happens to inter vene between a cue and its eventual re sponse. Smooth pursuit movements are not necessarily "reflex matching of eye to tar get velocity." Smooth pursuit may form part of a strategy to reduce predictable large position error during the latent period re quired for saccade. Such smooth eye move ments may even be in the opposite direc tion to a smoothly moving target. It is quite clear that the oculomotor system is not a simple servo-mechanism. H U M A N LENS CURVATURE
M. Howcroft and J. A. Parker (Toronto) Twenty-six pairs of frozen cadaver lenses were sectioned and photographed. Aspheric and spheric conic functions were then calcu lated for the anteroposterior cross-sectional profiles using a program for least squares fit to a conic section. A test of inter- vs. intrasubject variabil ity for the spheric functions was significant at a level of .01. The mean aspheric radius was 8 mm for the anterior surface of the lens and 5.5 mm for the posterior surface. Corresponding values for the spheric radius were 8.9 mm and 5.9 mm. The functions derived showed the anterior of the lens to be hyperbolic and the posterior parabolic. THE
TOOLS OF VISUAL
TESTING
J. A. Parker (Toronto) The indications and methods of testing
NOVEMBER, 1974
visual acuity, field, color, adaptation, ocu lar circulation, and electrophysiology provide the clinician with an insight into the loca tion of disease and to its extent, i.e., focal or diffuse. Serial testing provides a sensi tive index of progression or resolution of disease. These tests combined with the ge netic history and visible pathology allow the clinician to establish a diagnosis or prog nosis. ANALYZING THE ELECTRORETINOGRAM
J. A. Orpin (Toronto) Some of the peaks in the electroretino gram arise from quite different groups of cells. There are many feedback mechanisms at play both ionic and humoral associated with the firing of the amacrine, bipolar, and ganglion cells. Two techniques developed in our labora tory aid in the assessment of the electro retinogram. These are electrical filtering to determine how the energy is distributed in the frequency spectrum, and total energy computation to determine the efficiency with which the retina releases its electrochemical energy. Clinically we have obtained the follow ing findings which tended to verify those of other workers in the field: a diminished electroretinogram usually represents pro found and widespread macular degeneration. Findings suggestive of macular degenera tion are low b-wave, disappearance of the oscillatory potentials, and reduced energy content in the frequency range 8-40 Hz and also around 140 Hz. Most macular degener ation patients had electroretinographic changes regardless of whether their visual acuity was good or poor. The electroretino gram is usually normal if only the choroid, pigment epithelium, or rods and cones are damaged. P. K.
BASU
AMERICAN JOURNAL OF OPHTHALMOLOGY
not mean that there is a large "saccadic dead zone" of radius 17-30 min of arc; rather some of the responses are drifts, or se quences of tiny saccades that can only be detected by contact lens techniques. "Sac cadic suppression" is not necessarily a marked effect and saccades are not based simply on the retinal position of the tar get—-the eye responds to cues delivered dur ing saccades (dark-adapted eye, no back ground) and makes allowance for any other saccadic movement that happens to inter vene between a cue and its eventual re sponse. Smooth pursuit movements are not necessarily "reflex matching of eye to tar get velocity." Smooth pursuit may form part of a strategy to reduce predictable large position error during the latent period re quired for saccade. Such smooth eye move ments may even be in the opposite direc tion to a smoothly moving target. It is quite clear that the oculomotor system is not a simple servo-mechanism. H U M A N LENS CURVATURE
M. Howcroft and J. A. Parker (Toronto) Twenty-six pairs of frozen cadaver lenses were sectioned and photographed. Aspheric and spheric conic functions were then calcu lated for the anteroposterior cross-sectional profiles using a program for least squares fit to a conic section. A test of inter- vs. intrasubject variabil ity for the spheric functions was significant at a level of .01. The mean aspheric radius was 8 mm for the anterior surface of the lens and 5.5 mm for the posterior surface. Corresponding values for the spheric radius were 8.9 mm and 5.9 mm. The functions derived showed the anterior of the lens to be hyperbolic and the posterior parabolic. THE
TOOLS OF VISUAL
TESTING
J. A. Parker (Toronto) The indications and methods of testing
NOVEMBER, 1974
visual acuity, field, color, adaptation, ocu lar circulation, and electrophysiology provide the clinician with an insight into the loca tion of disease and to its extent, i.e., focal or diffuse. Serial testing provides a sensi tive index of progression or resolution of disease. These tests combined with the ge netic history and visible pathology allow the clinician to establish a diagnosis or prog nosis. ANALYZING THE ELECTRORETINOGRAM
J. A. Orpin (Toronto) Some of the peaks in the electroretino gram arise from quite different groups of cells. There are many feedback mechanisms at play both ionic and humoral associated with the firing of the amacrine, bipolar, and ganglion cells. Two techniques developed in our labora tory aid in the assessment of the electro retinogram. These are electrical filtering to determine how the energy is distributed in the frequency spectrum, and total energy computation to determine the efficiency with which the retina releases its electrochemical energy. Clinically we have obtained the follow ing findings which tended to verify those of other workers in the field: a diminished electroretinogram usually represents pro found and widespread macular degeneration. Findings suggestive of macular degenera tion are low b-wave, disappearance of the oscillatory potentials, and reduced energy content in the frequency range 8-40 Hz and also around 140 Hz. Most macular degener ation patients had electroretinographic changes regardless of whether their visual acuity was good or poor. The electroretino gram is usually normal if only the choroid, pigment epithelium, or rods and cones are damaged. P. K.
BASU