Evaluation of the color vision acuity pattern of undergraduates of health courses in a Brazilian university / Avaliação do padrão de acuidade visual para cores de acadêmicos da área de saúde em Universidade brasileira

ABSTRACT Objective: The goal of the study is to analyze the color vision acuity pattern in undergraduates of health courses and to discuss the impact of these diseases in this population. Color deficiencies interfere significantly in the daily routine of professionals in the health area who need to discern different color hues in several situations of their everyday practice. Methods: Sixty-four volunteers, undergraduates of health courses of the Federal University of Alfenas (UNIFAL-MG), participated in the study. One man was excluded because he did not fit the inclusion criteria. Two groups were analyzed according to sex with the Farnsworth Munsell 100-Hue test. Results: There were no significant differences between the eyes and between the groups analyzed. The color vision acuity pattern is between 35 and 40, according to the Total Error Score. The gender issue does not influence the general pattern of the color vision acuity of the health courses undergraduates when those with color vision disorders are removed. Conclusion: Screenings and guidance should be given to undergraduates of health courses so that, aware of their condition of presenting some type of color disorder, they shall make the appropriate decision on which career to follow so that such limitation does not interfere with the quality of their daily life.

RESUMO Objetivo: O objetivo do estudo é analisar a acuidade visual média para cores de estudantes da área de saúde e discutir o impacto das doenças que a afetam nessa população. Deficiências cromáticas interferem de forma significativa no dia a dia de profissionais da área da saúde que necessitam de discernir diferentes matizes em diversas situações de sua prática profissional. Métodos: Participaram da pesquisa 64 voluntários, estudantes de cursos da área de saúde da Universidade Federal de Alfenas, sendo que 1 homem foi excluído por não se adequar aos critérios de inclusão. Dois grupos foram analisados, de acordo com o sexo, com o teste de Farnsworth Munsell 100-Hue. Resultados: Não houve diferenças significativas entre os olhos e entre os grupos analisados. O padrão de visão de cores encontra-se entre 35 e 40, de acordo com a Pontuação do Erro Total. A questão de gênero não influencia no padrão geral da qualidade de visão de cores de estudantes da área de saúde, quando retirados aqueles que apresentam distúrbios da visão cromática. Conclusão: Devem ser realizadas triagens e orientação para estudantes de cursos da área de saúde para que, cientes da sua condição de apresentar algum tipo de distúrbio cromático, possam tomar a decisão adequada sobre qual carreira seguir para que tal limitação não interfira na qualidade de sua vida diária.

Psicofísica visual em caso de toxoplasmose ocular congênita / Visual psychophysics of congenital ocular toxoplasmosis case

Resumo A toxoplasmose ocular congênita é uma manifestação da infecção pelo parasita Toxoplasma gondii que ocorrer por meio placentário. Essa doença pode provocar importantes sequelas visuais. Este trabalho descreve um estudo de caso que utilizou avaliação psicofísica visual para descrever alterações funcionais decorrentes da toxoplasmose ocular congênita. A avaliação foi realizada em paciente de 30 anos, sexo masculino, residente em São Luís (MA), hígido com histórico da mãe ter apresentado infecção por toxoplasmose no período gestacional. Somente aos 26 anos foi feita uma avaliação médica detalhada que descreveu lesão na fóvea do olho direito. Na avaliação clínica clássica e na avaliação psicofísica visual, o paciente apresentou visão normal para o olho esquerdo. O olho direito apresentou baixa acuidade visual (valor decimal: 0,028), campo visual com escotomas localizados até 20º de ângulo visual e alteração da visão de cor. O estudo fornece informações médicas seguras e relevantes para o diagnóstico de toxoplasmose ocular congênita utilizando testes eficazes, de baixo custo e boa portabilidade, possibilitando uma alternativa de diagnóstico funcional para ser aplicada em locais de difícil acesso pelo interior do Brasil.

Abstract Congenital ocular toxoplasmosis is a manifestation of infection by the parasite Toxoplasma gondii that occurs through the placenta. This disease can lead to important visual sequelae. This paper describes a case report that uses visual psychophysics for the alterations of congenital ocular toxoplasmosis. The evaluation was performed in a 30-year-old man, a resident of São Luís (MA), with a history of his mother have had toxoplasmosis in the gestational period. Only at 26 years-old he did the detailed medical evaluation that described a lesion the fovea of the right eye. In the classic clinical examination and in visual psychophysical evaluation, the patient presented normal vision for the left eye. The right eye had low visual acuity (decimal value: 0.028), visual field with scotomas up to 20º of visual angle and alteration of color vision. The study offers safe and relevant medical information for the diagnosis of congenital ocular toxoplasmosis using a low-cost evaluation and with good portability, allowing a functional diagnostic alternative to be applied in places difficult to access in the interior of Brazil.

The Application of a New Maximum Color Contrast Sensitivity Test to the Early Prediction of Chiasma Damage in Cases of Pituitary Adenoma: The Pilot Study

PURPOSE: Our objective was to estimate the maximum color contrast sensitivity (MCCS) thresholds in individuals with chiasma opticum damage. METHODS: The pilot study tested 41 people with pituitary adenoma (PA) and 100 age- and gender-matched controls. Patients were divided into two groups according to PA size, PA ≤1 cm or PA >1 cm. A new MCCS test program was used for color discrimination. RESULTS: The mean total error score (TES) of MCCS was 1.8 in the PA ≤1 cm group (standard deviation [SD], 0.38), 3.5 in the PA >1 cm group (SD, 0.96), and 1.4 in the control group (SD, 0.31; p 1 cm (p < 0.01). In PA patients with normal VA, the TES was 2.35 times worse than that of healthy persons (p < 0.01).

Functional Magnetic Resonance Imaging Findings in Meares-Irlen Syndrome: A Pilot Sudy

PURPOSE: To investigate patterns of functional magnetic resonance imaging (fMRI) activation during sentence reading before and after wearing color-tinted lenses. METHODS: A total of 15 Meares-Irlen syndrome patients with a mean age of 23.4 years (range, 13 to 42 years) with no history of neurological or psychiatric disorders were scanned using a 3T MR scanner (Siemens, Tim-Trio, Germany). Each patient underwent two sessions of fMRI imaging (before and after MISViS color-tinted lens application). The fMRI paradigm included a block design of 20 seconds of rest (cross), 20 seconds of activation (sentence reading), and ten blocks (a total of 200 echo-planar image volumes) repeated for each session. Data preprocessing and analyses were performed using the SPM8 software package. RESULTS: The reading speed of patients improved more than 20% while wearing the selected lenses. When compared to the before-lens session, the after-lens session identified significant regions of activation in the left middle and superior temporal gyri (paired t-test; maximal z score, 5.38; Montreal Neurological Institute coordinate, -60 / -39 / 0; threshold at p < 0.05; corrected for multiple comparisons using family-wise error). No region of activation at the same threshold was found in the before-lens session as compared to the after-lens session. CONCLUSIONS: In the current study, we confirmed activation in the left middle and superior temporal gyri during sentence reading after wearing color-tinted lenses. These results could explain the effectiveness of color-tinted lenses in patients with Meares-Irlen syndrome.

Chromatic spatial contrast sensitivity estimated by visual evoked cortical potential and psychophysics

The purpose of the present study was to measure contrast sensitivity to equiluminant gratings using steady-state visual evoked cortical potential (ssVECP) and psychophysics. Six healthy volunteers were evaluated with ssVECPs and psychophysics. The visual stimuli were red-green or blue-yellow horizontal sinusoidal gratings, 5° × 5°, 34.3 cd/m2 mean luminance, presented at 6 Hz. Eight spatial frequencies from 0.2 to 8 cpd were used, each presented at 8 contrast levels. Contrast threshold was obtained by extrapolating second harmonic amplitude values to zero. Psychophysical contrast thresholds were measured using stimuli at 6 Hz and static presentation. Contrast sensitivity was calculated as the inverse function of the pooled cone contrast threshold. ssVECP and both psychophysical contrast sensitivity functions (CSFs) were low-pass functions for red-green gratings. For electrophysiology, the highest contrast sensitivity values were found at 0.4 cpd (1.95 ± 0.15). ssVECP CSF was similar to dynamic psychophysical CSF, while static CSF had higher values ranging from 0.4 to 6 cpd (P < 0.05, ANOVA). Blue-yellow chromatic functions showed no specific tuning shape; however, at high spatial frequencies the evoked potentials showed higher contrast sensitivity than the psychophysical methods (P < 0.05, ANOVA). Evoked potentials can be used reliably to evaluate chromatic red-green CSFs in agreement with psychophysical thresholds, mainly if the same temporal properties are applied to the stimulus. For blue-yellow CSF, correlation between electrophysiology and psychophysics was poor at high spatial frequency, possibly due to a greater effect of chromatic aberration on this kind of stimulus.

Efficiency of information coding in various L/M retinal cone ratios

Previous evidence has shown that the number of L and M cones in retina varies significantly between subjects. However, it is not clear how the variation of L/M ratio changes the behavioral performance of the subject. A model of transformation of data from retina to visual cortex for evaluation of various L/M cones ratios is presented. While L/M cone ratios close to 1 brings the best performance for one of postreceptoral [magnocellular] channels, we showed that the performance in the second channel [parvocells] will improve when the ratio furthers away from 1. effects of different ratios of S were also explored

A study on reproducing silicone shade guide for maxillofacial prostheses matching Indian skin color.

AIM: The value and success of a well-fitting and anatomically correct prosthesis are compromised if the color does not match the adjoining tissues. The use of powder colors to help develop a simplified silicone shade guide to aid in the fabrication of silicone facial prostheses for Indian patients has been described here. MATERIALS AND METHODS: Ten powder pigments were used to fabricate the silicone samples for three different subjects having light, medium and dark complexions who were separated into three groups depending on the value of their shades. Four-step wedge silicone samples with thickness variations of 1, 2, 4 and 6mm were fabricated. Visual assessment of the samples was done by four evaluators to check the agreement of color match. Data was statistically analyzed using kappa coefficients. RESULTS: The kappa values were found to be 0.09-0.44 for a light skin tone, -0.11 to 0.77 for medium skin and 0.44 to 0.85 for dark skin tones. This study showed that the samples of dark skin tone matched the skin tone well and showed a statistically good agreement. To further test the validity of these shade guides, facial silicone veneers were fabricated for three patients having light, medium and dark complexion. The color matching showed satisfactory results. CONCLUSION: The silicone veneers matched the skin color of all three patients. Hence, this shade guide will help clinicians to obtain a good intrinsic shade and minimize extrinsic coloration.

Discriminação de cores em profissionais da área técnica de empresa de material fotográfico / Color vision discrimination in employees of a photographic laboratory

OBJETIVO: Avaliar a discriminação de cores em profissionais da área técnica de empresa de material fotográfico. MÉTODOS: Foram incluídos 47 profissionais (37 homens) com idades variando de 18 a 41 anos (média 27,2 ± 5,6 anos), alocados em área técnica especializada em calibração e assistência de máquinas de revelação de fotos em 1 hora. O tempo de trabalho nesta atividade variou de 1 mês a 18 anos. O grupo controle constituiu de 22 voluntários (5 homens) com idades variando de 18 a 55 anos (Média 25,0 ± 10,6 anos). A discriminação de cores foi avaliada com o teste Farnsworth-Munsell 100-Hue. Os critérios de inclusão para os dois grupos foram: acuidade visual com a melhor correção óptica e > 0,1 logMAR, fundo de olho normal, ausência de doenças hereditárias, sintomas visuais ou cirurgia ocular prévia. RESULTADOS: Vinte e quatro (51 por cento) profissionais do laboratório fotográfico apresentaram discriminação superior, comparados a 18 por cento dos voluntários. Vinte (42 por cento) apresentaram discriminação de cores dentro da média e 3 (7 por cento) apresentaram discriminação inferior. O índice de erros foi estatisticamente menor no grupo de profissionais quando comparado ao grupo controle (T=968.000, P=0,011). Não houve correlação entre o tempo de atividade na profissão e os resultados da discriminação de cores. CONCLUSÕES: Os profissionais da área técnica da empresa fotográfica mostraram discriminação de cores superior à do grupo controle.

PURPOSE: The objective of this study was to evaluate chromatic discrimination in employees of a photographic laboratory. METHODS: A total of 47 professional employees of the technical area devoted to calibration and technical assistance for one-hour photo machines (37 men), aged 18 to 41 years (mean of 27.2 ± 5.6 years). The period working in this function ranged from one month to 18 years. Twenty-two normal volunteers (5 men) aged 18-55 years (mean of 25.0 ± 10.6 years) were tested as a control group. Color discrimination was evaluated by the Farnsworth-Munsell 100-Hue test. The inclusion criteria were visual acuity > 0.1 logMAR, normal fundus, absence of hereditary eye disease, absence of visual symptoms or ocular surgery. RESULTS: Twenty-four people (51 percent) of the professional group presented superior color discrimination when compared to 18 percent of the control group. Twenty people (42 percent) presented average discrimination and 3 (7 percent) presented inferior discrimination. Color vision discrimination was statistically better in professionals when compared to controls (T=968.000, P=0.011). There was no correlation between the period working in the function and color discrimination. CONCLUSIONS: Technical professionals working in a photographic laboratory showed better color discrimination than controls.

Comparative evaluation of megadose methylprednisolone with dexamethasone for treatment of primary typical optic neuritis.

AIM: To compare the efficacy of intravenous methylprednisolone and intravenous dexamethasone on visual recovery and evaluate their side-effects for the treatment of optic neuritis. MATERIALS AND METHODS: Prospective, randomized case-controlled study including 21 patients of acute optic neuritis presenting within eight days of onset and with visual acuity less then 20/60 in the affected eye who were randomly divided into two groups. Group I received intravenous dexamethasone 200 mg once daily for three days and Group II received intravenous methylprednisolone 250 mg/six-hourly for three days followed by oral prednisolone for 11 days. Parameters tested were pupillary reactions, visual acuity, fundus findings, color vision, contrast sensitivity, Goldmann visual fields and biochemical investigations for all patients at presentation and follow-up. RESULTS: Both groups were age and sex-matched. LOGMAR visual acuity at presentation was 1.10 +/- 0.52 in Group I and 1.52 +/- 0.43 in Group II. On day 90 of steroid therapy, visual acuity improved to 0.28 +/- 0.33 in Group I and 0.36 +/- 0.41 in Group II ( P =0.59). At three months there was no statistically significant difference in the color vision, contrast sensitivity, stereoacuity, Goldman fields and the amplitude and latency of visually evoked response between the two groups. The concentration of vitamin C, glucose, sodium, potassium, urea and creatinine were within the reported normal limits. CONCLUSION: Intravenous dexamethasone is an effective treatment for optic neuritis. However, larger studies are required to establish it as a safe, inexpensive and effective modality for the treatment of optic neuritis.

Estudo eletrorretinográfico de visão cromática / Electroretinographic study of chromatic vision

OBJETIVO: O objetivo deste estudo é descrever o traçado eletrorretinográfico no gambá sul-americano (Didelphis aurita) obtido com estímulo cromático de comprimento de onda seletivo. O eletrorretinograma é o registro das variações de voltagem nas células retinianas, desencadeadas por estímulo luminoso. O eletrorretinograma representa a atividade elétrica combinada de diferentes células, e sofre variações dependendo da fisiologia retiniana e do método de exame. MÉTODOS: Foram registrados os eletrorretinogramas de seis animais em adaptação ao escuro utilizando filtros cromáticos Kodak Wratten®, e registrada a sensibilidade espectral para comprimentos de onda específicos nas faixas de cores do azul, verde, amarelo, laranja e vermelho. RESULTADOS: Os resultados eletrorretinográficos mais consistentes foram obtidos quando o animal foi estimulado por faixas espectrais seletivas, ao invés de luz branca; e são consistentes com a curva de absorbância das opsinas descritas em fotorreceptores de marsupiais. Estudos prévios sugeriram a tricromacia dos marsupiais por microespectrofotometria de opsinas e imuno-histoquímica de retina. Esse fundamento morfológico não tinha demonstração fisiológica eletrorretinográfica, até este estudo. CONCLUSÃO: O gambá sul-americano tem se mostrado interessante como animal experimental no estudo comparativo da fisiologia visual em mamíferos, especialmente no estudo filogenético da visão cromática. Os marsupiais apresentam um modelo retiniano que superpõe os sistemas fotópico e escotópico; e o gênero Didelphis conserva características encontradas em fósseis do período pleoceno. Portanto, o sistema visual de um marsupial resgata características dos primórdios da evolução dos mamíferos, até o desenvolvimento dos padrões retinianos modernos.

PURPOSE: To describe the electroretinogram of the South-American opossum (Didelphis aurita) obtained by chromatic stimulus of specific wavelengths. The electroretinogram records voltage variations of retinal cells triggered by light stimulation. The electroretinogram represents the combination of electric activity of many different cells and varies according to retinal physiology and examination methods. METHODS: We recorded the electroretinogram of six animals in dark adaptation using chromatic Kodak Wratten® filters, and recorded the spectral sensitivity to specific wavelengths in the spectrum of blue, green, yellow, orange and red light bands. RESULTS: The most consistent electrorretinographic results were obtained when the animals were stimulated by selective spectral bands instead of white light. These results are consistent with the absorbance curve of the opsins described in marsupial photoreceptors. Previous studies using microspectrophotometry of opsins and retinal immunohistochemistry suggested marsupial trichromacy. This morphologic knowledge has not before been physiologically demonstrated by electroretinographic methods. CONCLUSION: The South-American opossum has proven to be an interesting experimental animal for comparative visual physiology studies among other mammals, especially studies on phylogenetic of chromatic vision. The opossum represents a retinal model that superimposes both the photopic and scotopic systems; and the Didelphis genus shows few changes when compared to the fossils of the Pleocene period. Therefore the marsupial's visual system retrieves characteristics from ancient mammal evolution to the retinal patterns found in modern mammals.

Sentido cromático: tipos de defeitos e testes de avaliação clínica / Chromatic sense: types of defects and clinical evaluation tests

A avaliação do senso cromático tem grande valor na clínica oftalmológica, tanto para diagnóstico dos defeitos congênitos (daltonismo), como para diagnóstico e acompanhamento dos defeitos adquiridos. Diversos testes clínicos podem ser aplicados para esse fim. Porém, é necessário conhecermos a proposta e a sensibilidade de cada um deles, pois existem grandes variações de resultados, dependendo da doença que se procura diagnosticar, se congênita ou adquirida. Buscamos com este trabalho revisar os tipos de defeitos da sensibilidade cromática e fornecer informações sobre os principais testes utilizados, bem como sua melhor aplicação. Enfatizamos, ainda, a importância da padronização da iluminação do ambiente onde são aplicados esses testes.

Evaluation of the chromatic sense has a great value in ophthalmic practice, both for diagnosis of the congenital defects (daltonism), as well as for diagnosis and follow-up of acquired defects. Many clinical tests are available to be used for this purpose. However it is necessary to know the details and sensitivity of each test, since there are many variations in the results, depending on the searched condition, if congenital or acquired pathologies. Our goal is to review the types of defects of the chromatic sense and provide information about the main current available tests and their best purpose. We further emphasize the importance of standard illumination procedure in the application of the tests.

Avaliação da função visual em pacientes com distrofia de cones / Visual function assessment in patients with cone dystrophy

OBJETIVO: Avaliar a função visual pela eletrorretinografia de campo total e pela acuidade visual em pacientes com distrofia de cones. MÉTODOS: Um grupo de 23 pacientes (16 do sexo feminino e 7 do sexo masculino) com distrofia de cones foi avaliado no Laboratório de Eletrofisiologia Visual Clínica do Departamento de Oftalmologia da Universidade Federal de São Paulo. A avaliação constou de: sinais e sintomas, acuidade visual medida pela tabela ETDRS ou de Snellen e função retiniana pela eletrorretinografia de campo total. As amplitudes pico-a-pico (µV) e o tempo de culminação da onda-b (ms) foram comparadas com normas descritas na literatura. RESULTADOS: A acuidade visual no melhor olho variou de 0,07 a 3,00 logMAR (20/25-MM a 10 cm), com média de 0,85±0,64 logMAR (20/140). A média da amplitude pico-a-pico das respostas escotópicas de bastonetes foi de 144,29±80,05 µV com média do tempo de culminação da onda-b de 92,85±9,02 ms (normal para a idade). A média da amplitude pico-a-pico para respostas fotópicas de cones foi de 5,06±8,59 µV (reduzida para a idade) com média do tempo de culminação da onda-b de 43,4±14,5 ms (atrasado para a idade) nos pacientes com resposta detectável e para as respostas do flicker, a amplitude foi de 5,00±9,00 µV (reduzida para a idade) com média do tempo de culminação da onda-b de 32,90±12,87 ms (atrasado para a idade). CONCLUSÃO: A acuidade visual média encontrada neste grupo de pacientes com distrofia de cones foi de 0,85 logMAR (20/140). A fotofobia foi o sintoma mais freqüente juntamente com a baixa de visão e deficiência de visão de cores. Em 10/23 pacientes o diagnóstico foi feito pela eletrorretinografia, devido à ausência de alterações fundoscópicas.

Color vision in the comb frequency domain

In 1982, Horace Barlow considered the question of human trichromacy in the context of information theory: according to the Sampling Theorem, three types of receptors covering the visible spectrum (400-700 nm) might be sufficient to reconstruct the color signal. Although Barlow was led to reject the direct application of the Sampling Theorem to explain color dimensionality, the theoretical framework offers a fresh point of view for analyzing the color system in conjunction with the physical characteristics of natural color signals. This review aims to illustrate that if the strict mathematical reconstruction (as implied by the Sampling Theorem) is replaced by a pragmatic approximation of color signals, then trichromacy, with its subsequent opponent-color process, could be regarded as an optimization of color constancy abilities in the spectral environment of primates. Higher dimension systems (tetrachromacy) found in other species can also serve the purpose of color constancy optimization in environments where color signals exhibit a finer spectral structure.

O perfil oftalmológico dos candidatos à carterira de motorista na cidade de Pelotas - RS / Ophthalmological profile of the candidates for driving license in Pelotas city - RS

Objetivo: Estudar a acuidade visual dos candidatos a condutores de veículos da cidade de Pelotas e sua associação com as características sociodemográficas dos candidatos. Métodos; Foram examinados 1.010 candidatos a condutores em um serviço médico autorizado pelo Detran. Avaliou-se a acuidade visual, com e sem correção, bem como a sua relação com a visão de cores, sexo, idade e profissão dos entrevistados, por meio da análise de freqüências e de teste para associação. Resultados: Deste contingente 73,0 por cento eram do sexo masculino, 65,0 por cento tinham idade entre 18 e 45 anos, 51,4 por cento ocupavam o setor de serviços e 25,0 por cento utilizavam meio de correção visual: Sob o ponto de vista oftalmológico, 0,5 por cento dos entrevistados não poderiam dirigir veículos automotores e 4,7 por cento só poderiam obter habilitação para condução veicular; nas categorias A e B. Mostrou-se associada à acuídade visual baixa a maior longevidade. Conclusão: Baseado nos resultados, sugere-se menor intervalo de tempo para reavaliação visual dos motoristas das categorias C, D e E.

Discromatopsias congênitas e condução de veículos / Congenital dyschromatopsias and driving

Objetivo: Apresentar a importância do uso da tabela de Ishihara para o diagnóstico das discromatopsias congênitas e avaliação da incidência em motoristas, observando-se os erros mais comuns no teste da Caixa de Cores. Além disso, abordar a relação entre discromatopsias congênitas, condução de veículo e acidentes de tráfego. Métodos: Foram examinados 523 motoristas, seguindo as normas da resolução 734/89 do Contran. Os motoristas foram submetidos ao teste de cores com a Tabela de lshihara, e os que tinham discromatopsias foram submetidos ao teste da Caixa de Cores, com luzes dispostas como em um semáforo. Resultados: Encontrou-se uma incidência de discromatopsias de 5,5 por cento (29 pacientes). Destes, 3 pacientes foram excluídos do estudo, 16 possuíam o grau forte e 10, o grau moderado. Desse último grupo, 7 apresentaram-se com deuteranomalia e 3 com protanomalia. Dos 7 com deuteranomalia, 3 apresentaram alterações no teste da Caixa de Cores. Dos 3 com protanomalia, 1 paciente teve exame alterado. Dos pacientes de grau forte, 14 possuíam deuteranopia e 2 protanopia, sendo que todos apresentaram alterações no teste da Caixa de Cores. Conclusão: Todos os pacientes com discromatopsias de grau forte e metade dos pacientes com grau moderado cometeram erros no teste da Caixa de Cores. Conclui-se que não haveria necessidade de ser realizado o teste para diferenciar as cores, desde que se faça o uso da tabela de lshihara para diagnosticar as discromatopsias congênitas.

Wave onset in central gray matter - its intrinsic optical signal and phase transitions in extracellular polymers

The brain is an excitable media in which excitation waves propagate at several scales of time and space. ''One-dimensional'' action potentials (millisecond scale) along the axon membrane, and spreading depression waves (seconds to minutes) at the three dimensions of the gray matter neuropil (complex of interacting membranes) are examples of excitation waves. In the retina, excitation waves have a prominent intrinsic optical signal (IOS). This optical signal is created by light scatter and has different components at the red and blue end of the spectrum. We could observe the wave onset in the retina, and measure the optical changes at the critical transition from quiescence to propagating wave. The results demonstrated the presence of fluctuations preceding propagation and suggested a phase transition. We have interpreted these results based on an extrapolation from Tasaki's experiments with action potentials and volume phase transitions of polymers. Thus, the scatter of red light appeared to be a volume phase transition in the extracellular matrix that was caused by the interactions between the cellular membrane cell coat and the extracellular sugar and protein complexes. If this hypothesis were correct, then forcing extracellular current flow should create a similar signal in another tissue, provided that this tissue was also transparent to light and with a similarly narrow extracellular space. This control tissue exists and it is the crystalline lens. We performed the experiments and confirmed the optical changes. Phase transitions in the extracellular polymers could be an important part of the long-range correlations found during wave propagation in central nervous tissue

Comparison of the incidence of colour blindness between sections of Libyan and Indian populations.

Incidence of Red-Green colour blindness was studied in a Libyan population and was then compared with the same in two samples of Indian population. The incidence of the Red-Green colour defect was found to be 2.209% amongst the males and 0.0% amongst the females in the Libyan study. However, the incidence was only 1.841% amongst the ethnic Libyan males. This incidence was comparable with those reported from other African countries like Congo and Uganda. The incidence of Red-Green colour defect amongst the Indian males was found to be 2.295% while it was 0.840% amongst the Indian females.

Electrophysiological measurements of spectral sensitivities: a review

Spectral sensitivities of visual systems are specified as the reciprocals of the intensities of light (quantum fluxes) needed at each wavelength to elicit the same criterion amplitude of responses. This review primarily considers the methods that have been developed for electrophysiological determinations of criterion amplitudes of slow-wave responses from single retinal cells. Traditional flash methods can require tedious dark adaptations and may yield erroneous spectral sensitivity curves which are not seen in such modifications as ramp methods. Linear response methods involve interferometry, while constant response methods involve manual or automatic adjustments of continuous illumination to keep response amplitudes constant during spectral scans. In DC or AC computerized constant response methods, feedback to determine intensities at each walvelength is derived from the response amplitudes themselves. Although all but traditional flash methods have greater or lesser abilities to provide on-line determinations of spectral sensitivities, computerized constant response methods are the most satisfatory due to flexibility, speed and maintenance of a constant adaptation level.