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PubMed1997

Wavelength-dependent magnification and polychromatic image quality in eyes corrected for longitudinal chromatic aberration.

Theoretical calculations using a simple model eye in combination with achromatizing lenses or artificial pupils show that correcting wavelength-dependent refractive error or its effects can exaggerate wavelength-dependent magnification by up to a factor of 7. These calculations are confirmed experimentally, and their effects on retinal image quality are modeled. Because of the increased wavelength-dependent magnification, gains in polychromatic image quality produced by correcting wavelength-dependent refractive error (or minimizing its effects with small pupils) are generally restricted to a small region of the retina.

Color Perception↗
PubMed2005

Ocular manifestations of multiple sclerosis.

PURPOSE OF REVIEW: Multiple sclerosis is an autoimmune demyelinating disorder of the nervous system that is commonly manifested by visual system involvement and that may initially present with ophthalmologic symptoms. This paper reviews recent findings regarding the ocular manifestations in multiple sclerosis. RECENT FINDINGS: Manifestations of multiple sclerosis in the eye include both the afferent and efferent visual pathways. Optic neuritis, the most common ocular manifestation of multiple sclerosis, may be the initial clinical disease manifestation. Recent long-term follow-up data show that most patients with demyelinating optic neuritis have an excellent prognosis for recovery of central visual acuity. Evidence is emerging, however, for significant and broad reduction in both contrast sensitivity and color perception in multiple sclerosis patients despite near-normal visual acuities. Ocular motor deficits in multiple sclerosis include internuclear ophthalmoplegia and nystagmus, resulting in diplopia, oscillopsia, blurred visual, loss of stereopsis, and reading fatigue. Multiple sclerosis also may be associated with ocular inflammatory diseases, in particular pars planitis and retinal periphlebitis. SUMMARY: Ocular findings may be initial manifestations of multiple sclerosis and may predict additional demyelinating events. Recognizing these syndromes and signs will help clinicians to properly evaluate the patient, formulate an appropriate differential diagnosis, be able to discuss the prognosis with the patient, and help develop an effective therapeutic plan.

Eye Diseases↗
PubMed1984

Variations of colour vision in a New World primate can be explained by polymorphism of retinal photopigments.

The squirrel monkey (Saimiri sciureus) exhibits a polymorphism of colour vision: some animals are dichromatic, some trichromatic, and within each of these classes there are subtypes that resemble the protan and deutan variants of human colour vision. For each of ten individual monkeys we have obtained (i) behavioural measurements of colour vision and (ii) microspectrophotometric measurements of retinal photopigments. The behavioural tests, carried out in Santa Barbara, included wavelength discrimination, Rayleigh matches, and increment sensitivity at 540 and 640 nm. The microspectrophotometric measurements were made in London, using samples of fresh retinal tissue and a modified Liebman microspectrophotometer: the absorbance spectra for single retinal cells were obtained by passing a monochromatic measuring beam through the outer segments of individual rods and cones. The two types of data, behavioural and microspectrophotometric, were obtained independently and were handed to a third party before being interchanged between experimenters. From all ten animals, a rod pigment was recorded with lambda max (wavelength of peak absorbance) close to 500 nm. In several animals, receptors were found that contained a short-wave pigment (mean lambda max = 433.5 nm): these violet-sensitive receptors were rare, as in man and other primate species. In the middle- to long-wave part of the spectrum, there appear to be at least three possible Saimiri photopigments (with lambda max values at about 537,550 and 565 nm) and individual animals draw either one or two pigments from this set, giving dichromatic or trichromatic colour vision. Thus, those animals that behaviourally resembled human protanopes exhibited only one pigment in the red-green range, with lambda max = 537 nm; other behaviourally dichromatic animals had single pigments lying at longer wavelengths and these were the animals that behaviourally had higher sensitivity to long wavelengths. Four of the monkeys were behaviourally judged to be trichromatic. None of the latter animals exhibited the two widely separated pigments (close to 535 and 567 nm) that are found in the middle- and long-wave cones of macaque monkeys.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1999

The clinical and functional measurement of cortical (in)activity in the visual brain, with special reference to the two subdivisions (V4 and V4 alpha) of the human colour centre.

We argue below that, at least in studying the visual brain, the old and simple methods of detailed clinical assessment and perimetric measurement still yield important insights into the organization of the visual brain as a whole, as well as the organization of the individual areas within it. To demonstrate our point, we rely especially on the motion and colour systems, emphasizing in particular how clinical observations predicted an important feature of the organization of the colour centre in the human brain. With the use of data from functional magnetic resonance imaging analysed by statistical parametric mapping and independent component analysis, we show that the colour centre is composed of two subdivisions, V4 and V4 alpha the two together constituting the V4 complex of the human brain. These two subdivisions are intimately linked anatomically and act cooperatively. The new evidence about the architecture of the colour centre might help to explain why the syndrome, cerebral achromatopsia, produced by lesions in it is so variable.

Carbon Monoxide Poisoning↗
PubMedDate not supplied

Generalization of learning in three-and-a-half-month-old infants on the basis of amodal relations.

Infants of 3.5 months (N = 124) were given the opportunity to learn to relate two objects and their natural, distinctive sounds during a training phase. The objects and sounds were united by temporal synchrony and amodal audiovisual information specifying object composition. Infants then participated in one of three types of transfer tests (requiring low, moderate, or high degrees of generalization) to measure the extent to which intermodal knowledge generalized to a new task and across events (familiar events; change in color/shape; change in substance, motion, and color/shape). Results indicated that infants tested with the familiar events and with events of a new color/shape showed learning and transfer of knowledge. In contrast, infants tested with events of a new substance, motion, and color/shape showed no generalization of learning. Thus, infants of 3.5 months appear to show a moderate degree of generalization of intermodal knowledge across events. Although this knowledge is not restricted to the events of original learning, it cannot yet be flexibly extended across a variety of contexts.

Auditory Perception↗
PubMed2002

Color naming and the phototoxic effects of sunlight on the eye.

Many languages have no basic color term for "blue." Instead, they call short-wavelength stimuli "green" or "dark". We show that this cultural, linguistic phenomenon could result from accelerated aging of the eye because of high, chronic exposure to ultraviolet-B (UV-B) in sunlight (e.g., phototoxic lens brunescence). Reviewing 203 world languages, we found a significant relationship between UV dosage and color naming: In low-UV localities, languages generally have the word "blue"; in high-UV areas, languages without "blue" prevail. Furthermore, speakers of these non-"blue" languages often show blue-yellow color vision deficiency. We tested our phototoxicity hypothesis in a color-naming experiment, using computerized, colorimetric simulations of Munsell colors as viewed through clear and brunescent lenses. As predicted, our young subjects used "blue" as in English when the simulated lens was clear, but named colors as in tropical languages when the lens was dense. Our within-subjects design precludes a cultural explanation for this result.

Adolescent↗
PubMed2005

The molecular basis of variation in human color vision.

Common variation in red-green color vision exists among both normal and color-deficient subjects. Differences at amino acids involved in tuning the spectra of the red and green cone pigments account for the majority of this variation. One source of variation is the very common Ser180Ala polymorphism that accounts for two spectrally different red pigments and that plays an important role in variation in normal color vision as well as in determining the severity of defective color vision. This polymorphism most likely resulted from gene conversion by the green-pigment gene. Another common source of variation is the existence of several types of red/green pigment chimeras with different spectral properties. The red and green-pigment genes are arranged in a head-to-tail tandem array on the X-chromosome with one red-pigment gene followed by one or more green-pigment genes. The high homology between these genes has predisposed the locus to relatively common unequal recombination events that give rise to red/green hybrid genes and to deletion of the green-pigment genes. Such events constitute the most common cause of red-green color vision defects. Only the first two pigment genes of the red/green array are expressed in the retina and therefore contribute to the color vision phenotype. The severity of red-green color vision defects is inversely proportional to the difference between the wavelengths of maximal absorption of the photopigments encoded by the first two genes of the array. Women who are heterozygous for red and green pigment genes that encode three spectrally distinct photopigments have the potential for enhanced color vision.

Color Perception↗
PubMed2005

Long-term macular function in eyes with central serous chorioretinopathy.

BACKGROUND: This study aimed to investigate the long-term effects of central serous chorioretinopathy (CSCR) on macular function. METHODS: Sixty-two eyes of 31 patients were included in this study. All patients were diagnosed with unilateral CSCR at the Retina Unit of the Ophthalmology Department, Trakya University Medical Faculty, and had a post-attack bilateral visual acuity of 6/6 and a follow-up period of a minimum of 6 months. Visual function was assessed using the Amsler grid, 40-hue colour discrimination test, visual field examination by means of Octopus automatic perimeter and Cambridge contrast sensitivity tests. RESULTS: Of the 31 patients, 71% were men and 29% were women, with a mean age of 39.3 +/- 7.6 years. The patients had a mean follow-up period of 50.6 +/- 40.5 months after the acute attack. Metamorphopsia was observed in 67.7% of the cases with CSCR. A colour discrimination defect was found in 48.4% of the CSCR eyes and in 54.8% of the fellow eyes. As compared with the fellow eyes, the mean deviation in the central 10 degrees of visual field was significantly higher (t = 2.9, P = 0.007) and the mean contrast sensitivity score was significantly lower (t = -3.2, P = 0.004) in the CSCR eyes. DISCUSSION: Patients with unilateral CSCR were observed to have long-term bilateral colour discrimination defects, and eyes with clinical CSCR were determined to have central relative scotoma and loss of contrast sensitivity.

Adult↗
PubMed2002

Protan colour vision deficiency and road accidents.

BACKGROUND: Protans are precluded from holding a commercial driver's licence in Australia because they have a substantially reduced ability to see red lights and have more road accidents involving signal lights. This exclusion has been in place since 1994 but is likely to be abandoned following a current review of medical standards for commercial drivers. This paper reviews the level of risk of road accidents due to protan colour vision deficiency. It also addresses the question of whether it is fair to regard all protans as having a higher risk of road accident because some protans might have a sensitivity to red light that is as good as that of some people with normal colour vision. METHODS: Data of two studies by Verriest and co-workers are re-analysed to estimate the degree of overlap of the protan and colour normal distributions of sensitivity to red light. RESULTS: Field trial data show that protans have a very reduced visual range for red signals compared to colour normal observers but there is considerable variability among both classes of observers and the distributions do overlap. However, some variability is due to differences in observers' choices of a detection criterion, their speed of response and the measurement method. A laboratory study of the spectral sensitivity of protan and colour normal subjects that largely removes these sources' variability shows that all protans have a sensitivity to red light that is less than that of the least sensitive colour normal. CONCLUSION: It is reasonable to conclude that all protans, regardless of the severity of their defect, have a lesser ability to see red signals than colour vision normal observers and for that reason will have a higher risk of road accident.

Accidents, Traffic↗
PubMed2003

Does the Farnsworth D15 test predict the ability to name colours?

BACKGROUND: The Farnsworth D15 test is designed to categorise colour vision deficiency as severe or moderate. The level of difficulty of the test was set so that those who passed it should be able to recognise surface colour codes, such as those used for electrical wiring. The test is widely used to provide advice to patients with abnormal colour vision and is often used for occupational selection when reliable recognition of surface colour codes is required. However, there has been only one previous study of the correlation between performance at the D15 test and the naming of surface colour codes and there has been no study of whether a person who passes the D15 can reliably name surface colours. METHODS: One hundred and two people aged 11 to 65 years with abnormal colour vision were recruited from consecutively presenting optometric patients and were asked to name the colours of fabric, paint and cotton thread samples. There were 10 colours in each class of material and the samples were presented in a large (five to 10 degree angular subtense) and small size (2.5 deg and a single thread). The errors made were compared to those made by an age-matched control group of equal size with normal colour vision. RESULTS: The correlations between the Farnsworth D15 colour confusion index and colour naming errors were 0.62 for the large stimuli and 0.73 for the small stimuli. Its sensitivity and specificity identifying those who made more errors than the worst performing colour normal person were 0.80 and 0.69 (large stimuli) and 0.75 and 0.71 (small stimuli). A Nagel anomaloscope range of less than 35 scale units provides essentially the same sensitivity and specificity. CONCLUSIONS: About 40 per cent of those with abnormal colour vision can name the main colours correctly under good visibility conditions. The D15 test is an imperfect predictor of those who can name surface colour codes correctly but it does provide useful information for general counselling. It is not suitable as a single test for occupational selection because it will pass 20 per cent who cannot name surface colours correctly and fail 30 per cent who can. In occupations in which recognition of surface colour codes is of critical importance, it may be best not to select people with abnormal colour vision because of the lack of a colour vision test that is a perfect predictor of the ability to recognise surface colours.

Adolescent↗
PubMed2005

Five cricketers with abnormal colour vision.

Five cricketers with abnormal colour vision, all of whom had mild deuteranomaly, reported occasions when they had lost sight of the ball when the background was the green grass of the playing field or the green of grassy banks or trees surrounding the playing field. While these five cricketers demonstrate that mild deuteranomaly does not preclude playing cricket successfully at a competitive level, their responses to questions at interview suggest that those with more severe forms of abnormal colour vision may be at a disadvantage. This conclusion is consistent with the under-representation of abnormal colour vision in a sample of first class county cricketers in England reported by Goddard and Coull (BMJ 1994; 309 1684-1685).

Adult↗
PubMedDate not supplied

What does it look like and what can it do? Category structure influences how infants categorize.

Despite a large body of research demonstrating the kinds of categories to which infants respond, few studies have directly assessed how infants' categorization unfolds over time. Four experiments used a visual familiarization task to evaluate 10-month-old infants' (N = 98) learning of exemplars characterized by commonalities in appearance or function. When learning exemplars with a common function, infants initially responded to the common feature, apparently forming a category, and only learned the individual features with more extensive familiarization. When learning exemplars with a common appearance, infants initially learned the individual features and apparently only formed a category with more extensive familiarization. The results are discussed in terms of models of category learning.

Association Learning↗