The determination of the central static visual acuity, presentation of a modified Landolt C chart

1991 ◽  
Vol 78 (3-4) ◽  
pp. 219-223 ◽  
Author(s):  
G. H. Jonkers ◽  
J. Burger
Keyword(s):  
Visual Acuity ◽  
Landolt C

Color stimuli perception in presence of light scattering

2006 ◽  
Vol 23 (3-4) ◽  
pp. 597-601 ◽  
Author(s):  
MARIS OZOLINSH ◽  
MICHÉLE COLOMB ◽  
GATIS IKAUNIEKS ◽  
VARIS KARITANS
Keyword(s):  
Visual Acuity ◽  
Light Scattering ◽  
Luminance Contrast ◽  
White Background ◽  
Color Contrast ◽  
Entire Area ◽  
Red Color ◽  
Blue Component ◽  
Different Color ◽  
Landolt C

Perception of different color contrast stimuli was studied in the presence of light scattering: in a fog chamber in Clermont-Ferrand and in laboratory conditions where light scattering of similar levels was obtained, using different light scattering eye occluders. Blue (shortest wavelength) light is scattered in fog to the greatest extent, causing deterioration of vision quality especially for the monochromatic blue stimuli. However, for the color stimuli presented on a white background, visual acuity in fog for blue Landolt-C optotypes was higher than for red and green optotypes on the white background. The luminance of color Landolt-C optotypes presented on a LCD screen was chosen corresponding to the blue, green, and red color contributions in achromatic white stimuli (computer digital R, G, or B values for chromatic stimuli equal to RGB values in the achromatic white background) that results in the greatest luminance contrast for the white–blue stimuli, thus advancing the visual acuity for the white-blue stimuli. Besides such blue stimuli on the white background are displayed with a uniform, spatially unmodulated distribution of the screen blue phosphor emission over the entire area of the screen including the stimulus C optotype area. It follows that scattering, which has the greatest effect on the blue component of screen luminance, has the least effect on the perception of white–blue stimuli.

Visual Acuity Affected by Size Perception Based on Convergence Cue

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 354-354
Author(s):  
H Shinoda ◽  
M Ikeda
Keyword(s):  
Visual Acuity ◽  
Visual System ◽  
Retinal Image ◽  
White Paper ◽  
Retinal Size ◽  
Size Perception ◽  
Convergence Angle ◽  
Threshold Size

Increasing (or decreasing) the convergence angle can shrink (or expand) the perceived size of an object without changing its retinal size (Oyama, 1974 Perception & Psychophysics16 175 – 182). Here we address the question whether such a change in perceived size affects visual acuity. We investigated the effects of perceived size on the legibility of letters, using a telestereoscope consisting of four mirrors to control the observer's convergence angle while keeping the size of the retinal image constant. The targets were photocopies of ordinary Japanese books containing both types of Japanese characters, kana and kanji. The former is a phonetic character and simpler than the latter. Letters were printed in black on white paper. First, we demonstrated that letters do become more legible (illegible) as perceived size expands (shrinks), although their retinal size does not change. Then, we measured the size of the convergence angle at which letters became legible. The ‘threshold’ size of the convergence angle was obtained for several retinal sizes (0.1 to 0.2 deg) of letters, and for kana and kanji, respectively. Four subjects participated in the experiment. The result shows that the threshold convergence angle for legibility decreases as the retinal size of letters decreases, so that the minimum retinal size of legible letters depends linearly on the convergence angle. The results implicate contributions from higher levels of the visual system to the determination of visual acuity.

The Accuracy of Drivers' Judgments of the Effects of Headlight Glare on Their Own Visual Acuity

Perception ◽  
10.1068/p7814 ◽  
2014 ◽  
Vol 43 (11) ◽  
pp. 1203-1213 ◽  
Author(s):  
Ashley A Stafford Sewall ◽  
Stephanie A Whetsel Borzendowski ◽  
Richard A Tyrrell
Keyword(s):  
Visual Acuity ◽  
Older Drivers ◽  
Visual Performance ◽  
High Beam ◽  
Disability Glare ◽  
Landolt C

Drivers' judgments of the magnitude of disability glare caused by high-beam headlights may not match actual declines in visual performance. This study investigated younger and older drivers' beliefs about their own visual performance in the presence of headlight glare. Eleven older drivers and seventeen younger drivers judged the distance at which they would just be able to recognize the orientation of a white Landolt C if it were present adjacent to the headlamps of a stationary opposing vehicle at night. The younger participants were generally accurate in their estimates of the recognition distance of the stimulus, while older participants significantly overestimated both their own acuity and the effect of glare on their vision. From this study, we see that older drivers' judgments about the disabling effects of oncoming headlights may be systematically inaccurate. These misperceptions about headlight glare may help explain why drivers tend to underuse high beams.

A Modification of Goldmann’s Apparatus for the Objective Determination of the Visual Acuity

1951 ◽  
Vol 122 (6) ◽  
pp. 368-374 ◽  
Author(s):  
M.A. Bouman ◽  
Ten Doesschate ◽  
G.J. du Marchie Sarvaas
Keyword(s):  
Visual Acuity ◽  
Objective Determination

Visual Acuity at Hyperbaric Air Pressure

1976 ◽  
Vol 43 (3) ◽  
pp. 983-986 ◽  
Author(s):  
N. A. M. Schellart
Keyword(s):  
Visual Acuity ◽  
Pressure Chamber ◽  
Air Pressure ◽  
Considerable Reduction ◽  
Open Sea ◽  
Landolt C

The visual acuity of five divers in a dry pressure chamber was measured with a Landolt C test. Only one of them showed a significant reduction at 7.0 atm. These results contrast sharply with open sea experiments, which show a considerable reduction at much lower pressures (Baddeley, 1968). It is suggested that besides stresses, luminance differences, also turbidity, as a function of depth may account for the discrepancy.

scholarly journals Contrast Ratios, Colour Elements, and Polarities in Visual Acuity Measurements

2018 ◽  
Vol 7 (3.11) ◽  
pp. 89
Author(s):  
Ai Hong Chen ◽  
Nurulain Muhamad
Keyword(s):  
Visual Acuity ◽  
Contrast Ratio ◽  
Rank Test ◽  
Friedman Test ◽  
Contrast Polarity ◽  
Signed Rank ◽  
Wilcoxon Signed Rank Test ◽  
Signed Rank Test ◽  
Lower Contrast ◽  
Landolt C

This study was aimed to investigate the effects of contrast ratios, colour elements, and polarities on visual acuity measurements. The visual acuities of 18 subjects were measured using 6 different modifications of the Landolt C chart in a 4-metre LogMAR design: (M1) black-on-white [contrast ratio: 0.8]; (M2) white-on-black [contrast ratio: 0.8]; (M3) black-on-white [contrast ratio: 0.5]; (M4) yellow-on-green [contrast ratio: 0.8]; (M5) yellow-on-green [contrast ratio: 0.5]; and (M6) black-on-yellow [contrast ratio: 0.8]. Comparative analysis was performed to examine the effects of the three aforementioned parameters on visual acuity measurements. The visual acuities were found to be significantly different between the contrast ratios of 0.5 and 0.8, regardless of whether colour elements were present (black-on-white) or otherwise (yellow-on-green) [Friedman test: c2 (3) = 24.24, p < 0.05]. Interestingly, the LogMAR score was found to be significantly different between the yellow-on-green and black-on-yellow chart designs when the contrast ratio remained constant at 0.8 [Wilcoxon signed-rank test: z = 2.950, p < 0.05]. However, the effect of contrast polarity (positive/ negative) on visual acuity was not significant when the contrast ratio was fixed at 0.8 [Wilcoxon signed-rank test: z = 0.318, p > 0.05].  A lower contrast ratio and mid-range wavelength colour reduced visual acuity. The effect of contrast polarity without colour elements on visual acuity was negligible.  

Patient‐specific determination of change in ocular spherical aberration to improve near and intermediate visual acuity of presbyopic eyes

2018 ◽  
Vol 12 (4) ◽  
pp. e201800259 ◽  
Author(s):  
Naren Shetty ◽  
Shruti Kochar ◽  
Prajakta Paritekar ◽  
Pablo Artal ◽  
Rohit Shetty ◽  
...  
Keyword(s):  
Visual Acuity ◽  
Spherical Aberration ◽  
Patient Specific ◽  
Specific Determination

Visual acuity as measured with Landolt C chart and Early Treatment of Diabetic Retinopathy Study (ETDRS) chart

2010 ◽  
Vol 249 (4) ◽  
pp. 601-605 ◽  
Author(s):  
Hsi-Kung Kuo ◽  
Ming-Tse Kuo ◽  
Ing-Soo Tiong ◽  
Pei-Chang Wu ◽  
Yung-Jen Chen ◽  
...  
Keyword(s):  
Visual Acuity ◽  
Diabetic Retinopathy ◽  
Early Treatment ◽  
Landolt C
Sign in / Sign up

Export Citation Format

Share Document