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Biomedical subjects

I C Wood

Publications and source records attributed to I C Wood.

9 recordsLinked to original sources
PubMed1992

Computerized Arden grating technique for the measurement of the contrast sensitivity function.

We developed a computerized contrast sensitivity function (CSF) measurement technique using a computer graphics board to reproduce Arden grating type stimuli. The reliability of the procedure was examined by evaluating the standard deviation of repeated test differences. The validity of the procedure was tested by comparison with both a manual method of adjustment technique and with Regan low contrast letter charts. The procedure has been performed at a number of exposure speeds to account for the effect of reaction time and attention of the results. The optimum exposure time for the procedure has been found to be greater than or equal to 22 s. As a result of the benefits of automation the test is quick, produces test-retest correlation coefficients for the five spatial frequencies tested which are similar to those for the method of adjustment procedure (0.76 to 0.91 for the computerized test, 0.66 to 0.88 for the signal generator measurements), and produces values which correspond closely with the method of adjustment measurement. It has the advantages of utilizing hardware already available in many computer systems, having a constant mean luminance across the screen, and having a constant and optimized presentation time.

Adult↗
PubMed1992

Inter-observer variability in a computer-assisted optic nerve head assessment system.

A computer-assisted optic nerve head analysis system was used to measure parameters of the optic nerve head from one eye from each of 15 subjects. The subjects comprised three groups of five, being glaucomatous, ocular hypertensive, and normal. The 15 images produced were analysed in a randomized masked fashion by ten observers of varying levels of experience to test the inter-observer variability of the measurements. An analysis of variance demonstrated significant differences in the measurements made by the different observers. Fisher's F-test showed that all the parameters assessing the pallor area of the optic nerve head had significantly lower inter-image variance (reported previously) compared with inter-observer variance (at the 5% level). Variability in taking measurements of the pallor area of the optic nerve head is mainly due to observer variations rather than the image variations.

Glaucoma↗
PubMed1991

Computer-assisted optic nerve head assessment.

An IBM-compatible microcomputer-based system has been developed for the assessment of pallor area size, shape and degree of pallor in the optic nerve head. The system allows the instantaneous capture of optic nerve head images, and software analysis of these images produces measurements of the pallor area in about 2 min. The various methods of image analysis are presented. These are enhancement, thresholding, and digital filtering for edge detection. The results of their application to the images of the optic nerve head are shown. The results of the system's analysis on a particular optic nerve head are also shown. The potential uses and difficulties of such a system are discussed.

Algorithms↗
PubMed1991

Inter- and intra-image variability in computer-assisted optic nerve head assessment.

A computer-assisted system for optic nerve head analysis was used to measure one eye from each of 15 subjects. These comprised three groups of five, being glaucomatous, ocular hypertensive, and normal subjects. Each eye was imaged with the system 10 times. The 150 images produced were analysed in a randomized masked fashion to test the inter-image variability of the measurements. Linear pallor: disc ratios had mean coefficients of variation of 6.6% (normal), 4.8% (ocular hypertensive) and 2.6% (glaucomatous). This trend of reducing coefficient of variation from normal to ocular hypertensive to glaucomatous was reflected in other parameters also. Intra-image variability was assessed by analysing one image from each subject 10 times, in a randomized masked fashion. The mean coefficients of variation of the linear pallor: disc ratios were 6.3% (normal), 3.6% (ocular hypertensive) and 3.2% (glaucomatous). Fisher's F-test showed that no parameters had significantly lower intra-image rather than inter-image variance (at the 5% level). Variability is apparently due to operator variations rather than the image variations.

Glaucoma↗
PubMed1978

Contrast threshold of random dot stereograms in anisometropic amblyopia: A clinical investigation.

The contrast thresholds of random dot stereograms were obtained for both anisometropic amblyopic and normal patients. The elevation of the contrast threshold found in both amblyopic and non-amblyopic eyes of the anisometropes reflects the relative strength of the binocular inhibition mechanism present. These findings were related to the standard clinical tests used in this investigation and other recent psychophysical and physiological investigations.

Amblyopia↗
PubMed1976

Stereopsis measured by random-dot patterns--a new clinical test.

Comparative measures are presented of stereo-acuity by random-dot stereograms using a phase difference haploscope and a Titmus stereogram. Using two groups of fifteen subjects each, one with full binocular vision and the other of small-angle strabismic amblyopes, greater discrimination between subject groups was found with the random-dot stereograms. It is concluded that random-dot stereograms produced by crossed Polaroid would be a more effective clinical means of determining stereo-acuity.

Amblyopia↗
PubMed1976

An acquired color defect of the opponent-color system.

An acquired unilateral color defect in a 22-year-old man has been investigated with standard clinical tests and by using techniques which, it is thought, test specifically for the sensitivity of the luminance and opponent-color systems. The spectral sensitivity of the defective left eye, using 1 degree 200 ms. test flashes on a white background, has a single broad peak at about 550 nm. and resembles the photopic luminosity curve; in contrast, the normal curve, measured in the same conditions, has three peaks at about 440, 520, and 600 nm. However, the subject's spectral sensitivity curve for detecting 20 Hz. flicker is quite normal and is similar to his curve for 200 ms. flashes. It has recently been proposed that the three peaks of the normal curve for 200 ms. flashes reflect the activity of the opponent-color system, whereas the single peak for flicker detection is related to the luminance system. The preceding observations may thus be interpreted in terms of a specific loss of the subject's opponent-color system and this would explain his poor color discrimination. His luminance system appears to be normal, and evidence is presented for the maintained function of red- and green-sensitive (but not blue-sensitive) cones. The spectral sensitivity of the subject's right eye is nearly normal, suggesting a precortical origin of the defect; however, there seems to be some abnormality in this eye, indicating a less developed form of the same defect.

Adult↗
PubMed1975

The accommodative response in amblyopia.

The accommodative response of normal and amblyopic subjects was measured over a range of stimulus values from two to seven D with a laser optometer incorporating the Badal system. The stimulus and response were found to be linearly related for both normal and amblyopic eyes, but the response of the amblyopic eye to the higher values of stimulus was reduced.

Accommodation, Ocular↗