ON THE VARIABILITY OF CRITICAL ILLUMINATION FOR FLICKER FUSION AND INTENSITY DISCRIMINATION

From the data of experiments with bees in which threshold response is employed as a means of recognizing visual discrimination between stripes of equal width alternately illuminated by intensities I1 and I2, it is shown that the detectable increment of intensity ΔI, where ΔI = I2 - I1, is directly proportional to σI2 (I1 being fixed). From tests of visual acuity, where I1 = 0 and the width of the stripes is varied, σI2 = kI2 + const.; here I2 = ΔI, and ΔI/I2 = 1. When the visual excitability of the bee is changed by dark adaptation, λI ≡ kΔI (= k' σΔI) = k'' I + const. For the measurements of critical illumination at threshold response to flicker, σI2 (= σΔI) = k I2 = k' ΔI + const. The data for critical illumination producing threshold response to flicker in the sun-fish Lepomis show for the rods σI2 = K I2 for the cones σI2 = K'(I2 + const.). The data thus indicate that in all these experiments essentially the same visual function is being examined, and that the recognition of the production of a difference in effect by alternately illuminated stripes takes place in such a way that d (ΔI)/d (σI2) = const., and that ΔI is directly proportional to I (or "I2," depending on the nature of the experiment). It is pointed out that the curve for each of the cases considered can be gotten equally well if mean I or σI is plotted as a function of the independent variable involved in the experiment. Certain consequences of these and related facts are important for the treatment of the general problem of intensity discrimination.

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THE INFLUENCE OF LIGHT ADAPTATION ON SUBSEQUENT DARK ADAPTATION OF THE EYE

The Journal of General Physiology ◽

10.1085/jgp.20.6.831 ◽

1937 ◽

Vol 20 (6) ◽

pp. 831-850 ◽

Cited By ~ 177

Author(s):

Selig Hecht ◽

Charles Haig ◽

Aurin M. Chase

Keyword(s):

Visual Acuity ◽

Maximal Function ◽

Dark Adaptation ◽

Light Adaptation ◽

Intensity Discrimination ◽

Human Eye ◽

Rod Function ◽

Cone Adaptation

The course of dark adaptation of the human eye varies with the intensity used for the light adaptation which precedes it. Preadaptation to intensities below 200 photons is followed only by rod adaptation, while preadaptation to intensities above 4000 photons is followed first by cone adaptation and then by rod adaptation. With increasing intensities of preadaptation, cone dark adaptation remains essentially the same in form, but covers an increasing range of threshold intensities. At the highest preadaptation the range of the subsequent cone dark adaptation covers more than 3 log units. Rod dark adaptation appears in two types—a rapid and a delayed. The rapid rod dark adaptation is evident after preadaptations to low intensities corresponding to those usually associated with rod function. The delayed rod dark adaptation shows up only after preadaptation to intensities which are hundreds of times higher than those which produce the maximal function of the rods in flicker, intensity discrimination, and visual acuity. The delayed form remains essentially constant in shape following different intensities of preadaptation. However, its time of appearance increases with the preadaptation intensity; after the highest preadaptation, it appears only after 12 or 13 minutes in the dark. These two modes of rod dark adaptation are probably the expression of two methods of formation of visual purple in the rods after its bleaching by the preadaptation lights.

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THE VARIABILITY OF INTENSITY DISCRIMINATION BY THE HONEY BEE IN RELATION TO VISUAL ACUITY

The Journal of General Physiology ◽

10.1085/jgp.16.5.787 ◽

1933 ◽

Vol 16 (5) ◽

pp. 787-793 ◽

Cited By ~ 4

Author(s):

Ernst Wolf ◽

W. J. Crozier

Keyword(s):

Visual Acuity ◽

Honey Bee ◽

Power Function ◽

Intensity Discrimination ◽

Frequency Of Occurrence ◽

Threshold Response ◽

The Difference

Variation in the determined magnitudes of the difference in brightness between alternating members of a system of stripes requisite for the elicitation of a threshold response in bees shows that the intensity of excitation, as a function of width of stripe and of intensity of illumination, is determined by the intensity of illumination and by the frequency of occurrence of divisions between bright and less bright bars. The variation of ΔI is limited by the intensity of excitation, so that the curves relating P.E. (ΔI/I) have the same form in relation to I as do the curves for ΔI/I. The limiting rule according to which P.E. ΔI is a power function of I for stripes of maximum usable width is departed from more and more markedly, for lower intensities, as narrower stripes are employed.

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Night vision in barn owls: Visual acuity and contrast sensitivity under dark adaptation

Journal of Vision ◽

10.1167/12.13.4 ◽

2012 ◽

Vol 12 (13) ◽

pp. 4-4 ◽

Cited By ~ 24

Author(s):

J. Orlowski ◽

W. Harmening ◽

H. Wagner

Keyword(s):

Visual Acuity ◽

Contrast Sensitivity ◽

Dark Adaptation ◽

Night Vision ◽

Barn Owls

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Natural History of Idiopathic Epiretinal Membrane in Eyes with Good Vision Assessed by Spectral-Domain Optical Coherence Tomography

Ophthalmologica ◽

10.1159/000437058 ◽

2015 ◽

Vol 234 (2) ◽

pp. 91-100 ◽

Cited By ~ 12

Author(s):

Ik Soo Byon ◽

Gang Yun Pak ◽

Han Jo Kwon ◽

Kyong Ho Kim ◽

Sung Who Park ◽

...

Keyword(s):

Optical Coherence Tomography ◽

Visual Acuity ◽

Natural History ◽

Visual Function ◽

Epiretinal Membrane ◽

Membrane Separation ◽

Early Stage ◽

Optical Coherence ◽

Idiopathic Epiretinal Membrane ◽

History Of

Purpose: To investigate the natural history of idiopathic epiretinal membrane (ERM) in eyes with good visual function using optical coherence tomography (OCT). Methods: Sixty-two eyes of 58 patients with idiopathic ERM, visual acuity of 20/40 or better, and no significant metamorphopsia were included. The best corrected visual acuity (BCVA), central macular thickness (CMT), membrane configuration, and ellipsoid zone signal data over 24 months were retrospectively analyzed. Based on OCT findings, ERM configurations were categorized as global attachment (GA), partial attachment (PA), pseudohole, and vitreomacular traction (VMT). Results: The mean BCVA and CMT did not change significantly between baseline and 24 months. GA, PA, pseudohole, and VMT types were observed in 33, 19, 9, and 1 eye at baseline, and in 20, 22, 10, and 1 eye at 24 months, respectively. A membrane configuration change was noted in 24 eyes (38.7%) during follow-up, and the distribution shifted from GA to the other types (p < 0.001). Six eyes had visual loss due to membrane progression, and 4 eyes had spontaneous membrane separation. Of the 10 eyes with progression or separation, 6 were of the PA type. Conclusions: Although the BCVA remains stable over 2 years in most idiopathic ERM eyes with good visual function at baseline, the membrane configuration may change, affecting visual acuity. The GA type would be an early stage, and the PA type is prone to changes in visual acuity.

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The Cockroach DCMD Neurone: I. Lateral Inhibition and the Effects of Light- and Dark-adaptation

Journal of Experimental Biology ◽

10.1242/jeb.99.1.61 ◽

1982 ◽

Vol 99 (1) ◽

pp. 61-90 ◽

Cited By ~ 1

Author(s):

DONALD H. EDWARDS

Keyword(s):

Lateral Inhibition ◽

Dark Adaptation ◽

Light Adaptation ◽

Absolute Intensity ◽

Recurrent Network ◽

Light Spot ◽

Movement Detector ◽

Threshold Response ◽

Inhibitory Network ◽

Local Background

1. The responses of the cockroach descending contralateral movement detector (DCMD) neurone to moving light stimuli were studied under both light- and dark-adapted conditions. 2. With light-adaptation the response of the DCMD to two moving 2° (diam.) spots of white light is less than the response to a single spot when the two spots are separated by less than 10° (Fig. 2). 3. With light-adaptation the response of the DCMD to a single moving light spot is a sigmoidally shaped function of the logarithm of the light intensity (Fig. 3a). With dark-adaptation the response of a DCMD to a single moving light spot is a bell-shaped function of the logarithm of the stimulus intensity (Fig. 3b). The absolute intensity that evokes a threshold response is about one-and-a-half log units less in the dark-adapted eye than in the light-adapted eye. 4. The decrease in the DCMD's response that occurs when two stimuli are closer than 10°, and when a single bright stimulus is made brighter, indicates that lateral inhibition operates among the afferents to the DCMD. 5. It is shown that this inhibition cannot be produced by a recurrent lateral inhibitory network. A model of the afferent path that contains a non-recurrent lateral inhibitory network can account for the response/intensity plots of the DCMD recorded under both light-adapted and dark-adapted conditions. 6. The threshold intensity of the DCMD is increased if a stationary pattern of light is present near the path of the moving spot stimulus. This is shown to be due to a peripheral tonic lateral inhibition that is distinct from the non-recurrent lateral inhibition described earlier. 7. It is suggested that the peripheral lateral inhibition acts to adjust the threshold of afferents to local background light levels, while the proximal non-recurrent network acts to enhance the acuity of the eye to small objects in the visual field, and to filter out whole-field stimuli.

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Arteriovenous malformations in the optic apparatus: systematic literature review and report of four cases

Journal of Neurosurgery ◽

10.3171/2021.1.jns204162 ◽

2021 ◽

pp. 1-11

Author(s):

Visish M. Srinivasan ◽

Phiroz E. Tarapore ◽

Stefan W. Koester ◽

Joshua S. Catapano ◽

Caleb Rutledge ◽

...

Keyword(s):

Visual Acuity ◽

Visual Field ◽

Visual Function ◽

Arteriovenous Malformations ◽

Vascular Malformations ◽

Visual Fields ◽

Optic Tract ◽

Visual Disturbance ◽

Visual Field Defects ◽

Subtotal Resection

OBJECTIVE Rare arteriovenous malformations (AVMs) of the optic apparatus account for < 1% of all AVMs. The authors conducted a systematic review of the literature for cases of optic apparatus AVMs and present 4 cases from their institution. The literature is summarized to describe preoperative characteristics, surgical technique, and treatment outcomes for these lesions. METHODS A comprehensive search of the English-language literature was performed in accordance with established Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to identify all published cases of AVM in the optic apparatus in the PubMed, Web of Science, and Cochrane databases. The authors also searched their prospective institutional database of vascular malformations for such cases. Data regarding the clinical and radiological presentation, visual acuity, visual fields, extent of resection, and postoperative outcomes were gathered. RESULTS Nine patients in the literature and 4 patients in the authors’ single-surgeon series who fit the inclusion criteria were identified. The median age at presentation was 29 years (range 8–39 years). Among these patients, 11 presented with visual disturbance, 9 with headache, and 1 with multiple prior subarachnoid hemorrhages; the AVM in 1 case was found incidentally. Four patients described prior symptoms of headache or visual disturbance consistent with sentinel events. Visual acuity was decreased from baseline in 10 patients, and 11 patients had visual field defects on formal visual field testing. The most common visual field defect was temporal hemianopia, found in one or both eyes in 7 patients. The optic chiasm was affected in 10 patients, the hypothalamus in 2 patients, the optic nerve (unilaterally) in 8 patients, and the optic tract in 2 patients. Six patients underwent gross-total resection; 6 patients underwent subtotal resection; and 1 patient underwent craniotomy, but no resection was attempted. Postoperatively, 9 of the patients had improved visual function, 1 had no change, and 3 had worse visual acuity. Eight patients demonstrated improved visual fields, 1 had no change, and 4 had narrowed fields. CONCLUSIONS AVMs of the optic apparatus are rare lesions. Although they reside in a highly eloquent region, surgical outcomes are generally good; the majority of patients will see improvement in their visual function postoperatively. Microsurgical technique is critical to the successful removal of these lesions, and preservation of function sometimes requires subtotal resection of the lesion.

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IX.—On the Toothing of Un-round Discs which are intended to Roll upon each other

Transactions of the Royal Society of Edinburgh ◽

10.1017/s0080456800090645 ◽

1877 ◽

Vol 28 (1) ◽

pp. 191-195

Author(s):

Edward Sang

Keyword(s):

General Problem ◽

The Sun ◽

Turn On ◽

Angular Velocities

The construction of the toothed wheels used in machinery gives rise to some very interesting investigations in the geometry of motion. The general problem is so to shape the contours as that they shall remain in contact while the wheels turn on their centres with uniform angular velocities.The inquiry becomes more extensive when the velocities of the wheels are to be variable; as, for example, when we seek to imitate the revolutions of the planets round the sun, and for that purpose introduce the equation of the centre.In these cases the wheels are supposed to turn on fixed centres; but we may still farther extend the scope of our researches by removing the centres and subjecting the discs to the single condition that they roll upon each other.If two discs A and B touch at the point S, and if they so move as that the point of contact shifts equally along the two boundaries, they are said to roll on each other; that is to say, if we measure equal distances ST, SV along the two boundaries, the points T and V will come together in the course of the movements.

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Prognostic factors for postoperative visual outcome in surgically treated suprasellar meningiomas

Medicinski pregled ◽

10.2298/mpns1606146g ◽

2016 ◽

Vol 69 (5-6) ◽

pp. 146-152 ◽

Cited By ~ 2

Author(s):

Desanka Grkovic ◽

Sofija Davidovic

Keyword(s):

Visual Acuity ◽

Tumor Size ◽

Visual Function ◽

Tumor Resection ◽

Visual Outcome ◽

Duration Of Symptoms ◽

Postoperative Visual Acuity ◽

Preoperative Visual Acuity ◽

History Of ◽

Meningioma Surgery

Introduction. The prognosis of postoperative visual acuity in patients with surgically treated suprasellar meningiomas is influenced not only by the size and precise localization of meningiomas in the optochiasmatic region and their compressive effect, but also by certain parameters, such as the age of patient, duration of symptoms, and preoperative visual acuity. The purpose of this study was to analyze the influence of these factors on postoperative visual acuity in the patients with surgically treated optochiasmatic meningioma as well as to determine their prognostic value in the recovery of visual function after surgery. Material and Methods. The study sample consisted of 43 patients operated for suprasellar meningioma. All tumors were diagnosed by computed tomography or nuclear magnetic resonance scans. Visual acuity was analyzed both before surgery and six months after surgery. The effects of age, preoperative visual loss, duration of visual symptoms and tumor size on visual outcome were analyzed. Results. Postoperative improvement of visual acuity was observed in 50% of eyes (68.4% of patients). Visual outcome was better in the younger patients. The patients with better preoperative visual acuity had better postoperative visual acuity outcome. Chances of achieving better postoperative visual function and favorable tumor resection outcome were inversely proportional to the increased length of history of disease and tumor size. Conclusion. Postoperative visual acuity prognosis in suprasellar meningioma surgery was favorably affected by the mean duration of symptoms of less than 24 months, tumor size less than 30 mm, and preoperative visual acuity loss below 0.1.

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