The notion that forces from the eyelids can alter the shape of the cornea has been proposed for many years. In recent times, there has been a marked improvement in our ability to measure and define the corneal shape, allowing subtle changes in the cornea to be measured. These improvements have led to the findings that pressure from the eyelids can cause alterations in corneal shape following everyday visual tasks such as reading. There are also theories to suggest that pressure from the eyelids may be involved in the aetiology of corneal astigmatism. In this program of research, a series of experiments were undertaken to investigate the influence of the eyelids on the shape of the cornea. In the first experiment, an investigation into the diurnal variation of corneal shape was carried out by measuring corneal topography at three different times (approximately 9 am, 1 pm and 5 pm) during the day over three days of the week (Monday, Tuesday and Friday). Highly significant diurnal changes were found to occur in the corneal topography of 15 of the 17 subjects. This change typically consisted of horizontal bands of distortion in the superior, and to a lesser extent, inferior cornea, increasing throughout the day (and returning to baseline the next morning). These changes appeared to be related to forces from the eyelids on the anterior cornea. Some changes were also found in corneal astigmatism. Corneal astigmatism power vector J0 (astigmatism 90/180°) was found to increase slightly over the course of the week. Whilst the changes in astigmatism were small in magnitude, this result leaves open the possibility that pressure from the eyelid may cause changes in corneal astigmatism. If pressure from the eyelids is involved in the aetiology of corneal astigmatism, then one may expect associations to exist between certain characteristics of the eyelids and corneal shape. An experiment was then undertaken to explore these possible associations. We defined the average morphology of the palpebral fissure in different angles of vertical gaze for 100 young normal subjects. This was achieved through analysis of digital images that were captured in primary gaze, 20° downgaze and 40° downgaze. Parameters defining the size, position, angle and contour of the eyelids were determined. Highly significant changes were found to occur in the palpebral fissure with downward gaze. The palpebral aperture narrows in downward gaze, and the angle of the eyelids changes from being slightly upward slanted in primary gaze, to being slightly downward slanted in downward gaze. The eyelid margin contour also flattens significantly in downward gaze. The average topography of the central and peripheral cornea was also defined for this same population. A technique was used that allowed the capture and subsequent combination of topography data from both the central and the peripheral cornea. The use of this technique provided a large corneal topography map, with data extending close to the limbus for each subject. Marked flattening was found to occur in the peripheral cornea and a conic section was found to be a poor descriptor of corneal contour in the periphery (i.e. greater than 6 mm diameter). Corneal astigmatism was also found on average to reduce in the periphery. However a number of distinct patterns of peripheral corneal astigmatism were noted in the population. Corneal astigmatism in the peripheral cornea was either found to remain stable (59% of subjects), increase (10% of subjects) or reduce (31% of subjects) in magnitude in comparison to the amount of central corneal astigmatism. We also investigated associations between the parameters defining the palpebral fissure and parameters describing corneal shape in this population of subjects. A number of highly significant associations were found between the morphology of the palpebral fissure in primary gaze and the shape of the cornea. A general tendency was found for subjects with wider horizontal palpebral fissure widths to exhibit larger corneas and also flatter central corneal powers. There were also highly significant associations found between the angle of the eyelids and the axis of corneal astigmatism, but not the magnitude of corneal astigmatism. The associations found between corneal astigmatism and palpebral fissure morphology is further evidence supporting the hypothesis that pressure from the eyelids is involved in the aetiology of corneal astigmatism. The results of these investigations have shown that corneal changes as a result of eyelid forces occur in the majority of young subjects tested over the course of a normal working day. The average morphology of the palpebral fissure and topography of the central and peripheral cornea has also been defined in detail for a large population of young subjects. Significant associations were found between corneal astigmatism and the morphology of the palpebral fissure. Whilst these results support a model of corneal astigmatism development based on eyelid morphology, they do not prove causation. Further research including measurement of eyelid pressure and corneal rigidity may aid in understanding the exact aetiology of the magnitude and axis of corneal astigmatism.

A relação trabalho e visão é tão remota que determinou a adaptação da espécie humana ao meio em que está inserida. Demonstrou-se que trabalhar em um ambiente confortável, sem doenças ocular, favorece o desempenho visual e aumenta a produtividade. Conhecer os efeitos do monitor de computador (VDT) sobre o sistema visual significa planejar melhor o ambiente de trabalho e a atividade laboral para se obter máximo conforto e produtividade. Este estudo teve como objetivo geral analisar as alterações do piscar, do filme lacrimal e da superfície ocular induzidas pelo uso de monitor de computador (VDT). Para sua realização efetivou-se um estudo transversal, descritivo, observacional, analítico, realizado na Volkswagen do Brasil, São José dos Pinhais (PR), tendo como amostra, a população de funcionários do setor administrativo que utiliza VDT, com idade acima de 18 anos, sem doenças da superfície ocular, sistema palpebral e lacrimal. O ambiente de trabalho foi caracterizado pela temperatura, grau de umidade, velocidade do ar e iluminamento. Preencheram os critérios de inclusão 108 funcionários (idade média 34,1±7,88 anos e tempo mínimo de utilização do VDT 6 horas/dia). Foram avaliados as sintomatologias, filmagem da face para mensuração do tempo entre piscadas na situação de conversação, exame do olho externo e biomicroscopia das pálpebras, conjuntiva e córnea, filmagem videoceratoscópica para determinar tempo de ruptura do filme lacrimal, avaliação da quantidade de lágrima do lago lacrimal pelo Zone-Quick Phenol Red Thread tear test, avaliação do epitélio corneano pelo teste da lissamina verde, filmagem da face dos sujeitos para mensuração do tempo entre piscadas em leitura de VDT. Ao final da jornada de trabalho, foram feitas a reavaliação do tempo de ruptura do filme lacrimal da quantidade de lágrima e a avaliação do epitélio corneano. Compararamse o tempo entre as piscadas em conversação e em uso de VDT e o tempo de ruptura do filme lacrimal, antes e ao final da jornada de trabalho. A comparação desses tempos classificou os sujeitos como expostos, com tempo médio de ruptura do filme lacrimal menor que o tempo médio entre piscadas e não expostos com tempo médio de ruptura do filme lacrimal maior que o tempo médio entre piscadas. Nas condições do estudo, em jornada de trabalho com tempo mínimo de 6 horas de uso de VDT, houve aumento da exposição da superfície ocular causada pelo aumento do tempo entre piscadas. O aumento da exposição da superfície ocular foi causado pela diminuição do tempo de ruptura do filme lacrimal constatado ao final da jornada de trabalho. O tempo entre piscadas na situação de leitura em VDT que foi significantemente maior que na situação de conversação. O tempo de ruptura do filme lacrimal, ao final da jornada de trabalho, foi significativamente menor que em seu início. A exposição ocular observada durante a jornada de trabalho com usuários de VDT, nas condições deste estudo, não causou alteração epitelial detectável ao teste da lissamina verde. Não houve alteração do volume lacrimal em olhos com exposição, antes da jornada de trabalho com VDT, nem houve alteração do volume lacrimal em olhos com exposição ocular, após a jornada de trabalho com VDT. / The relationship between work and vision is so remote that has determined the adaptation of human beings to the environment in which they are inserted. It has been demonstrated that working in a pleasant environment, without any ocular disease, has favored visual performance and increased productivity. Knowing the effects of video terminal display (VDT) on the visual system helps plan labor environments and labor activities more effectively so that optimal comfort and productivity are obtained. This transversal study, performed at Volkswagen do Brasil, São José dos Pinhais, PR, has the objective to investigate the influence of VDT labor activities on blinking, tear film and ocular surface, ocular exposure and amount of tear in the lacrimal lake. The population sample comprised VDT administrative department employees older than 18, without diseases on the ocular surface, tear film and blinking system. The evaluation of the working environment included measurements of temperature, humidity, air speed and lighting. One hundred and eight employees met the study criteria (mean age 34.1±7.88 and minimal VDT use time of 6 hours/day). Several evaluations were performed: the ocular surface symptomatology; the measurement of the blink time in conversation situations; the examination of the ocular surface and lacrimal film; a videokeratoscopy to establish the tear film break-up time; evaluation of the amount of tears of the lacrimal lake by means of the Zone-Quick Phenol Red Thread tear test; evaluation of the corneal epithelium by means of the lissamine green test; and determination of the blink time in VDT reading situations. At the end of the working period, the amount of tears and the corneal epithelium structure were re-evaluated. Comparisons between the blink time in conversation and VDT reading situations were performed before and at the end of the working day. The comparison data obtained classifies the subjects into two categories: exposed, with a tear film break-up time shorter than the mean time between blinks; and non-exposed, with tear film break-up time longer than the mean time between blinks. The findings obtained reveal that there was an increase in the ocular surface exposure caused by the increase in the time between blinks during the working period and increase of the ocular surface exposure caused by the decrease in the tear film break-up time determined at the end of the working day. The time between blinks at VDT reading situations was significantly longer than at conversation situations. The tear film break-up time at the end of the working day was significantly shorter than at the beginning. The ocular exposure during the VDT use has not caused epithelium alterations detectable at the lissamine green test. There were no alterations in the amount of tears in the eyes which underwent ocular exposure after VDT use situations.

A relação trabalho e visão é tão remota que determinou a adaptação da espécie humana ao meio em que está inserida. Demonstrou-se que trabalhar em um ambiente confortável, sem doenças ocular, favorece o desempenho visual e aumenta a produtividade. Conhecer os efeitos do monitor de computador (VDT) sobre o sistema visual significa planejar melhor o ambiente de trabalho e a atividade laboral para se obter máximo conforto e produtividade. Este estudo teve como objetivo geral analisar as alterações do piscar, do filme lacrimal e da superfície ocular induzidas pelo uso de monitor de computador (VDT). Para sua realização efetivou-se um estudo transversal, descritivo, observacional, analítico, realizado na Volkswagen do Brasil, São José dos Pinhais (PR), tendo como amostra, a população de funcionários do setor administrativo que utiliza VDT, com idade acima de 18 anos, sem doenças da superfície ocular, sistema palpebral e lacrimal. O ambiente de trabalho foi caracterizado pela temperatura, grau de umidade, velocidade do ar e iluminamento. Preencheram os critérios de inclusão 108 funcionários (idade média 34,1±7,88 anos e tempo mínimo de utilização do VDT 6 horas/dia). Foram avaliados as sintomatologias, filmagem da face para mensuração do tempo entre piscadas na situação de conversação, exame do olho externo e biomicroscopia das pálpebras, conjuntiva e córnea, filmagem videoceratoscópica para determinar tempo de ruptura do filme lacrimal, avaliação da quantidade de lágrima do lago lacrimal pelo Zone-Quick Phenol Red Thread tear test, avaliação do epitélio corneano pelo teste da lissamina verde, filmagem da face dos sujeitos para mensuração do tempo entre piscadas em leitura de VDT. Ao final da jornada de trabalho, foram feitas a reavaliação do tempo de ruptura do filme lacrimal da quantidade de lágrima e a avaliação do epitélio corneano. Compararamse o tempo entre as piscadas em conversação e em uso de VDT e o tempo de ruptura do filme lacrimal, antes e ao final da jornada de trabalho. A comparação desses tempos classificou os sujeitos como expostos, com tempo médio de ruptura do filme lacrimal menor que o tempo médio entre piscadas e não expostos com tempo médio de ruptura do filme lacrimal maior que o tempo médio entre piscadas. Nas condições do estudo, em jornada de trabalho com tempo mínimo de 6 horas de uso de VDT, houve aumento da exposição da superfície ocular causada pelo aumento do tempo entre piscadas. O aumento da exposição da superfície ocular foi causado pela diminuição do tempo de ruptura do filme lacrimal constatado ao final da jornada de trabalho. O tempo entre piscadas na situação de leitura em VDT que foi significantemente maior que na situação de conversação. O tempo de ruptura do filme lacrimal, ao final da jornada de trabalho, foi significativamente menor que em seu início. A exposição ocular observada durante a jornada de trabalho com usuários de VDT, nas condições deste estudo, não causou alteração epitelial detectável ao teste da lissamina verde. Não houve alteração do volume lacrimal em olhos com exposição, antes da jornada de trabalho com VDT, nem houve alteração do volume lacrimal em olhos com exposição ocular, após a jornada de trabalho com VDT. / The relationship between work and vision is so remote that has determined the adaptation of human beings to the environment in which they are inserted. It has been demonstrated that working in a pleasant environment, without any ocular disease, has favored visual performance and increased productivity. Knowing the effects of video terminal display (VDT) on the visual system helps plan labor environments and labor activities more effectively so that optimal comfort and productivity are obtained. This transversal study, performed at Volkswagen do Brasil, São José dos Pinhais, PR, has the objective to investigate the influence of VDT labor activities on blinking, tear film and ocular surface, ocular exposure and amount of tear in the lacrimal lake. The population sample comprised VDT administrative department employees older than 18, without diseases on the ocular surface, tear film and blinking system. The evaluation of the working environment included measurements of temperature, humidity, air speed and lighting. One hundred and eight employees met the study criteria (mean age 34.1±7.88 and minimal VDT use time of 6 hours/day). Several evaluations were performed: the ocular surface symptomatology; the measurement of the blink time in conversation situations; the examination of the ocular surface and lacrimal film; a videokeratoscopy to establish the tear film break-up time; evaluation of the amount of tears of the lacrimal lake by means of the Zone-Quick Phenol Red Thread tear test; evaluation of the corneal epithelium by means of the lissamine green test; and determination of the blink time in VDT reading situations. At the end of the working period, the amount of tears and the corneal epithelium structure were re-evaluated. Comparisons between the blink time in conversation and VDT reading situations were performed before and at the end of the working day. The comparison data obtained classifies the subjects into two categories: exposed, with a tear film break-up time shorter than the mean time between blinks; and non-exposed, with tear film break-up time longer than the mean time between blinks. The findings obtained reveal that there was an increase in the ocular surface exposure caused by the increase in the time between blinks during the working period and increase of the ocular surface exposure caused by the decrease in the tear film break-up time determined at the end of the working day. The time between blinks at VDT reading situations was significantly longer than at conversation situations. The tear film break-up time at the end of the working day was significantly shorter than at the beginning. The ocular exposure during the VDT use has not caused epithelium alterations detectable at the lissamine green test. There were no alterations in the amount of tears in the eyes which underwent ocular exposure after VDT use situations.