Louise L. Sloan

Congenital Achromatopsia: A Report of 19 Cases*

Studies were made of the visual functions of subjects with complete and incomplete achromatopsia, with particular emphasis on measurements of the rates of dark adaptation in a parafoveal region of the retina and at the fovea. When adequate preadaptation to a high luminance is achieved, the dark-adaptation curves reveal the presence of some form of photopic receptors in addition to the normal scotopic rods. Both types of receptor are present, not only in the paracentral retina, but also at the fovea.

The photopic acuity-luminance function with special reference to parafoveal vision

Abstract The linear relation between decimal acuity and log luminance, well established for the fovea, is also found for parafoveal areas of the retina. The parafoveal acuity-luminance function has a slower rate of change of acuity with log luminance and reaches maximal acuity at a lower luminance. Changes in retinal organization and their effects on the density of functional receptor units probably contribute to the observed regional differences.

Variation of acuity with luminance in ocular diseases and anomalies

SummaryStudies of the acuity-luminance function are reported for patients with reduced acuity resulting from optic nerve lesions, suppression amblyopias and retinal lesions of various sorts. The findings in all patients of the first two groups and in some of those with retinal lesions can be attributed almost entirely to the use of parafoveal or paramacular regions of the retina. The excentric viewing area is associated with a reduced rate of change of acuity with log luminance similar to that observed in the normal para-central retina. In some patients with retinal pathology involving the macular area the entire acuity-log I graph is shifted to the right on the intensity axis. As a result these patients require very high light intensities to attain their best visual acuity.RésuméLes variations de lacuité visuelle en fonction de la luminance ont été étudiées chez des patients atteints de lésions du nerf optique, damblyopie strabique ou de lésions rétiniennes diverses. Chez tous les malades des deux premiers groupes et chez certains appartenant au troisième les résultats sexpliquent prèsquentièrement par lutilisation de la région parafovéale ou paramaculaire. Chez certains patients du troisième groupe dont la macula est touchée, la courbe est déplacée vers la droite sur laxe des intensités et une très forte intensité lumineuse est nécessaire pour atteindre la meilleure acuité.ZusammenfassungDie Veränderungen der Sehschärfe bei wechselnder Leuchtdichte wurde bei Patienten mit Sehnervenleiden, Schielamblyopie und Netzhauterkrankungen verschiedener Art untersucht. Bei allen Kranken der ersten zwei Gruppen und bei einigen der dritten Gruppe lassen sich die Resultate durch die Benutzung der parafoveolären oder paramakularen Netzhautgegend erklären. Bei einzelnen Patienten der dritten Gruppe, bei denen die Makulagegend pathologisch verändert war, ist die Kurve auf der Intensitätenaxe nach rechts verschoben und es werden sehr starke Lichtintensitäten benötigt, um die bestmögliche Sehkraft zu erreichen.

Area and luminance of test object as variables in projection perimetry: Clinical studies of photometric dysharmony

Abstract The relationship between area and threshold luminance of the projected test object was measured for the standard background of the Goldmann perimeter, in normal eyes and in eyes with field defects associated with various forms of ocular disease or anomaly. Photometric dysharmony, characterized by a significantly greater increase in threshold for small than for large test objects, was noted in some cases. The findings do not support the hypothesis that photometric dysharmony is produced by retinal edema, since it was absent or slight in all patients with central serous retinopathy and was marked in some patients with achromatopsia. Its absence in congenital night blindness and in pigmentary degeneration of the retina suggests that photometric dysharmony occurs only when there is impairment of the cone receptor mechanism. When it is present, early field defects should be more easily detected by a decrease in size than by a decrease in luminance of the test object.

Color Signal Systems for the Red-Green Color Blind.* An Experimental Test of the Three-Color Signal System Proposed by Judd

An experimental investigation is made of Judd’s proposed three-color code for instrument panel lights. The adequacy of these specifications is tested using both normal and color-deficient subjects. It is shown that if certain specific limiting conditions are met as to the luminance, subtense, and chromaticity of the light signals, all normal observers and a majority of color-deficient observers can make the necessary identifications. The possible explanations for the poor performance of some, but not all, protanopes are discussed.

Recognition of Red and Green Point Sources by Color-Deficient Observers*

Determinations are made of the minimal intensities in mile-candles at which color-deficient observers could distinguish red and green point sources falling within or just outside the chromaticity limits proposed by Judd. For colors within these limits the minimal intensities are closely related to scores on the Air Forces Color Threshold Test. When slightly yellower greens are included the task is more difficult for the color-deficient observer.

Optical Magnification for Subnormal Vision: Historical Survey*†

Early attempts to provide optical magnification to compensate for subnormal visual acuity used small galilean telescopes, mounted in spectacle frames, giving magnifications ranging from 1.3 to 3×. They were seldom helpful in distance vision because of the restricted field, change of apparent distance, and inadequate magnification. Many used them only for reading, and obtained additional magnification from a reading cap of high dioptric power which permitted a close viewing distance. After about 1955, the interest in telescopic magnifiers was almost entirely replaced by two other developments. One emphasized the use of simple reading spectacles of high power. A second involved the search for inexpensive optical aids such as jeweller’s loupes, thread counters, magnifiers for inspection of coins or stamps, and similar devices developed for the normal eye. Trial-and-error prescription of these devices as reading aids was later superseded by more-systematic procedures based on measurement and classification of the available aids as to magnifying power and type. This led to the development of new optical aids to supplement those already available. Examination procedures were also devised to assist in selection of aids of the required power and type for each user.

Comparison of the Nagel Anomaloscope and a Dichroic Filter Anomaloscope

The Nagel Anomaloscope and a simple filter anomaloscope were used in testing 103 subjects with deficient color perception for red and green. The filter anomaloscope differentiates the deuteranomalous (DA) and the protanomalous types (PA), but does not distinguish types of defect among dichromats.A small number of subjects seemed to have a transitional defect between anomalous trichromasy and dichromasy. Evidence is presented suggesting that many if not all of these are actually dichromats, who give atypical responses because differences in saturation are mistaken for differences in hue.The two instruments agreed closely in their classifications of subjects as to type and degree of defect. The filter anomaloscope is the simpler in procedure and in interpretation of results.

New Methods of Rating and Prescribing Magnifiers for the Partially Blind

The conventional formula for the increase in size of the retinal image provided by a simple magnifier is M=D/4. This formula is based on arbitrary assumptions as to the accommodative powers exerted when the observer views a near object with and without the magnifier. Since these assumptions do not apply in a majority of cases, the conventional ratings of magnification are of limited use in the prescribing of reading aids for patients with subnormal vision. More realistic formulas are proposed which are applicable to many special cases, and which take account of the fact that the increase in size of the retinal image may depend upon the way in which the magnifier is used.It is shown that the dioptric power of the magnifier required by a given patient is determined primarily by (a) his visual acuity and (b) his near point of distinct vision. A simple test of near-acuity for meaningful text is described which gives direct and valid information as to the increase in size of the retinal image required for useful reading vision. Further studies are needed to determine the best method of measuring the accommodative powers of patients with subnormal vision.

Aniseikonia and the Howard-Dolman test.

The effects of artificial aniseikonic errors on the moving-rod type of depth-perception test were studied in two subjects. Aniseikonia in the horizontal meridian produced a constant error in the setting of the movable rod whose direction and magnitude varied with the direction and magnitude of the aniseikonia. In the Howard-Dolman test the constant errors were only one-third to one-half those predicted from the binocular disparity. In a modified test in which opposing monocular cues were eliminated, the settings showed the expected constant errors of about 65 mm for each one percent difference in the size of the ocular images. The mean variation about the average position of subjective equidistance showed considerable day-to-day variation.