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Los Angeles Ophthalmological Society
1409
SOCIETY PROCEEDINGS glaucoma. Gonioscopy has aided in our understanding of the pathologic processes of the visible angle and helps in planning the medical and surgical management of cases in which the chamber angle is concerned. CIRCULATORY ASPECTS OF THE GLAUCOMA PROBLEM
DR. J O H N N. EVANS delivered the annual
Mark J. Schoenberg Memorial Lecture. He discussed certain aspects of ocular circulation. He called attention to the fact that the aqueous and the vitreous might be termed the "fourth circulation." (The "third circulation" was a term created by Harvey Cushing in referring to the cerebrospinal system fluid.) He presented illustrations from original work which lent strength to the idea that the vitreous is probably much more active in a nutritive and dynamic sense than is usually recognized. He suggested that the remains of the vitreous vascular fetal system may act as cleavage planes to help conduct the aqueous element of the vitreous to the posterior drainage system by way of the perivascular spaces. He pointed out that the choroid in health is much thicker than we are led to believe from the study of histologie preparations. He discussed the possible mechanism of vitreous-chamber fluid pressure associated with the rapid changes in volume of the choroid which take place in nervous shock, and so forth. The mechanism taking part in such changes is related to the action of the so-called capillary sphincter muscles, the structure which he described in a communication about a year ago. He stressed the point that therapeutic and surgical measures should be designed especially for the'relief of vitreous pressures in cases of glaucoma. Dr. Evans illustrated his paper with numerous slides from original studies. (The lecture •will be published in an early issue of the JOURNAL.)
Bernard Kronenberg, Recording Secretary.
LOS ANGELES OPHTHALMOLOGICAL SOCIETY December, 1948 DR. WILLIAM ENDRES, chairman T H E TEXTBOOK RETINA AND THE REAL ONE
DR. GORDON L. WALLS of Berkeley
(by
invitation) presented an illustrated lecture correcting many of the errors and half truths concerning the retina as described in most textbooks. The retina does not end at the ora serrata, but at the margin of the pupil. In lowly vertebrates the sensory retina degenerates if the opticus is cut, but a new retina. regenerates from the ciliary epithelium, which is actually retinal tissue. The retina is not a mere part of a sensory organ. It is the visual sense organ, and more. All other parts of the globe are as much accessory as are extraglobar orbital structures. The retina is homologous with the whole thickness of the brain wall, and is more a sense organ since it contains its own associational systems mediating facilitative and inhibitional phenomena, and can almost "think." The retinal layers traditionally taught have no meaning. Functionally, the retina has only four layers: (1) the purely nutritive pigment epithelium; (2) the visual-cell layer; (3) the layer of internuncial neurons; and (4) the ganglion, so thinly distributed that it forms a "layer." At either side of the internuncial layer, funneling and spreading of excitation and inhibition are mediated by the horizontal and amacrine cells and by the diffuse dendrites of large bipolar and ganglion cells. Rods and cones are neither nerve cells nor neuro-epithelium, but modified ependymal cells which were formerly flagellated, as is shown by their cytogenesis as well as by their situation in the developing optic cup. The rods are not historically older than the cones, as is generally taught (and as is
1410
SOCIETY PROCEEDINGS
assumed in the Ladd-Franklin theory of color vision). But the first cones did not mediate color vision—nor did the first rods contain visual purple, which is by no means a primitive visual photochemical but an ingenious one which conveniently decolorizes in bright light (preventing dazzlement). Cones have secondarily given rise to rods, and vice versa, through evolutionary transmutations. The two are not immutable structural types. Pure-cone, diurnal animals have had nocturnal descendants with duplex and even pure-rod retinas. Human cones were derived from lemuroid rods and are not homologous with cones outside of the Primates. Human cones are not conical. Adequate micrologic methods show their outer segments to be cylindrical and as long as those of rods. Moreover, each cone outer segment is ensheathed by (and possibly continuous with) a tubular process from the nearest pigment-epithelium cell. This trophic arrangement, demanded by the elevated metabolism of the cones (as opposed to rods), explains why vision never returns perfectly after a detachment is repaired. The cones are not most numerous in the extramacular fundus and fewest at the ora; nor are the rods most numerous at the ora. 0sterberg found the densest rod population in a zone only S to 6 mm. from the fovea. The rods are actually denser here (160,000/sq. mm.) than are the cones in the fovea. What the textbooks call the "macula" is actually the area centralis. The fovea, properly, is the depression in this area. The macula lutea is by definition the region containing a yellow pigment. With a purple filter described by Walter Miles, the macular pigmentation can be seen entoptically. It is found to be actually smaller than the foveal pit, though textbooks describe the fovea as occupying a small portion of the macula. The human area centralis may have a diameter of 10 to 12 degrees, the foveal pit 6 to 7 degrees, the macula lutea 2 to 2.5 degrees; and, the rod-free spot is only 50
minutes of arc in diameter. The cones in this spot are slenderized to promote acuity and elongated to preserve their sensitivity. The center-to-center separation of adjacent foveal cones is 24 to 28 seconds, which happens to be about the value of the smallest resolution thresholds reported for Landolt-ring targets. But this is mere coincidence. Resolution thresholds may be made as small as desired with parallel-line targets, simply by increasing the thickness of the lines. The resolution target then intergrades with one presenting a bright line on a black field, and for such a line there is no minimal visible width. Resolution of lines does not require an unstimulated row of cones between stimulated rows, hence is not limited by the diameter of one cone. It is only necessary that the rows of cones be differentially stimulated; so, it is the intensity-discrimination function that sets the limit upon visual acuity: in resolution, one is discriminating intensities within the diffraction retinal image of the target. The conception of the mental image as being made up of dots, each contributed by a cone, is fallacious and outmoded. The "retinal local signs" so important in space perception are neither retinal nor local, but cortical and directional. The stimulation of a retinal point arouses a cortical point which now has information regarding oculocentric direction but not of distance, hence not of place. Space is more finely graduated than is the visual-cell mosaic (as vernier and motion acuities show), since the multiplication of paths between the cones and the cortex makes a great number of cortical elements correspond to two adjacent cones. Differential illumination of these cones can cause activity to "peak" in any one of many cortical cells, so that the spatial point may be directionalized between the produced axes of adjacent cones. Visual space is thus made subjectively "continuous." Orwyn H. Ellis, Recorder.
SOCIETY PROCEEDINGS glaucoma. Gonioscopy has aided in our understanding of the pathologic processes of the visible angle and helps in planning the medical and surgical management of cases in which the chamber angle is concerned. CIRCULATORY ASPECTS OF THE GLAUCOMA PROBLEM
DR. J O H N N. EVANS delivered the annual
Mark J. Schoenberg Memorial Lecture. He discussed certain aspects of ocular circulation. He called attention to the fact that the aqueous and the vitreous might be termed the "fourth circulation." (The "third circulation" was a term created by Harvey Cushing in referring to the cerebrospinal system fluid.) He presented illustrations from original work which lent strength to the idea that the vitreous is probably much more active in a nutritive and dynamic sense than is usually recognized. He suggested that the remains of the vitreous vascular fetal system may act as cleavage planes to help conduct the aqueous element of the vitreous to the posterior drainage system by way of the perivascular spaces. He pointed out that the choroid in health is much thicker than we are led to believe from the study of histologie preparations. He discussed the possible mechanism of vitreous-chamber fluid pressure associated with the rapid changes in volume of the choroid which take place in nervous shock, and so forth. The mechanism taking part in such changes is related to the action of the so-called capillary sphincter muscles, the structure which he described in a communication about a year ago. He stressed the point that therapeutic and surgical measures should be designed especially for the'relief of vitreous pressures in cases of glaucoma. Dr. Evans illustrated his paper with numerous slides from original studies. (The lecture •will be published in an early issue of the JOURNAL.)
Bernard Kronenberg, Recording Secretary.
LOS ANGELES OPHTHALMOLOGICAL SOCIETY December, 1948 DR. WILLIAM ENDRES, chairman T H E TEXTBOOK RETINA AND THE REAL ONE
DR. GORDON L. WALLS of Berkeley
(by
invitation) presented an illustrated lecture correcting many of the errors and half truths concerning the retina as described in most textbooks. The retina does not end at the ora serrata, but at the margin of the pupil. In lowly vertebrates the sensory retina degenerates if the opticus is cut, but a new retina. regenerates from the ciliary epithelium, which is actually retinal tissue. The retina is not a mere part of a sensory organ. It is the visual sense organ, and more. All other parts of the globe are as much accessory as are extraglobar orbital structures. The retina is homologous with the whole thickness of the brain wall, and is more a sense organ since it contains its own associational systems mediating facilitative and inhibitional phenomena, and can almost "think." The retinal layers traditionally taught have no meaning. Functionally, the retina has only four layers: (1) the purely nutritive pigment epithelium; (2) the visual-cell layer; (3) the layer of internuncial neurons; and (4) the ganglion, so thinly distributed that it forms a "layer." At either side of the internuncial layer, funneling and spreading of excitation and inhibition are mediated by the horizontal and amacrine cells and by the diffuse dendrites of large bipolar and ganglion cells. Rods and cones are neither nerve cells nor neuro-epithelium, but modified ependymal cells which were formerly flagellated, as is shown by their cytogenesis as well as by their situation in the developing optic cup. The rods are not historically older than the cones, as is generally taught (and as is
1410
SOCIETY PROCEEDINGS
assumed in the Ladd-Franklin theory of color vision). But the first cones did not mediate color vision—nor did the first rods contain visual purple, which is by no means a primitive visual photochemical but an ingenious one which conveniently decolorizes in bright light (preventing dazzlement). Cones have secondarily given rise to rods, and vice versa, through evolutionary transmutations. The two are not immutable structural types. Pure-cone, diurnal animals have had nocturnal descendants with duplex and even pure-rod retinas. Human cones were derived from lemuroid rods and are not homologous with cones outside of the Primates. Human cones are not conical. Adequate micrologic methods show their outer segments to be cylindrical and as long as those of rods. Moreover, each cone outer segment is ensheathed by (and possibly continuous with) a tubular process from the nearest pigment-epithelium cell. This trophic arrangement, demanded by the elevated metabolism of the cones (as opposed to rods), explains why vision never returns perfectly after a detachment is repaired. The cones are not most numerous in the extramacular fundus and fewest at the ora; nor are the rods most numerous at the ora. 0sterberg found the densest rod population in a zone only S to 6 mm. from the fovea. The rods are actually denser here (160,000/sq. mm.) than are the cones in the fovea. What the textbooks call the "macula" is actually the area centralis. The fovea, properly, is the depression in this area. The macula lutea is by definition the region containing a yellow pigment. With a purple filter described by Walter Miles, the macular pigmentation can be seen entoptically. It is found to be actually smaller than the foveal pit, though textbooks describe the fovea as occupying a small portion of the macula. The human area centralis may have a diameter of 10 to 12 degrees, the foveal pit 6 to 7 degrees, the macula lutea 2 to 2.5 degrees; and, the rod-free spot is only 50
minutes of arc in diameter. The cones in this spot are slenderized to promote acuity and elongated to preserve their sensitivity. The center-to-center separation of adjacent foveal cones is 24 to 28 seconds, which happens to be about the value of the smallest resolution thresholds reported for Landolt-ring targets. But this is mere coincidence. Resolution thresholds may be made as small as desired with parallel-line targets, simply by increasing the thickness of the lines. The resolution target then intergrades with one presenting a bright line on a black field, and for such a line there is no minimal visible width. Resolution of lines does not require an unstimulated row of cones between stimulated rows, hence is not limited by the diameter of one cone. It is only necessary that the rows of cones be differentially stimulated; so, it is the intensity-discrimination function that sets the limit upon visual acuity: in resolution, one is discriminating intensities within the diffraction retinal image of the target. The conception of the mental image as being made up of dots, each contributed by a cone, is fallacious and outmoded. The "retinal local signs" so important in space perception are neither retinal nor local, but cortical and directional. The stimulation of a retinal point arouses a cortical point which now has information regarding oculocentric direction but not of distance, hence not of place. Space is more finely graduated than is the visual-cell mosaic (as vernier and motion acuities show), since the multiplication of paths between the cones and the cortex makes a great number of cortical elements correspond to two adjacent cones. Differential illumination of these cones can cause activity to "peak" in any one of many cortical cells, so that the spatial point may be directionalized between the produced axes of adjacent cones. Visual space is thus made subjectively "continuous." Orwyn H. Ellis, Recorder.