Biomedical subjects

C Mermoud

Publications and source records attributed to C Mermoud.

9 recordsLinked to original sources

PubMed2002

Reading with multiple preferred retinal loci: implications for training a more efficient reading strategy.

The reading strategies in individuals with central scotomas and more than one preferred retinal locus (PRL) were investigated using a scanning laser ophthalmoscope in order to understand the visual requirements that lead to the need to use more than one PRL during reading. It was found that: (1) PRL function can be deduced from variation in PRL usage for different size and length of isolated words; (2) each subject used two or more PRL to accomplish the functions of global viewing and discrimination, suggesting that these are two of the minimum requirements for reading; (3) reading strategies can change depending on the position of words in visual space; (4) line-changing strategies can revert to horizontal and vertical component movements. These findings have implications for improving reading performance through training in patients with central scotomas.

Adult↗

PubMed1999

Does visual sensitivity improve between 5 and 8 years? A study of automated visual field examination.

In 74 normal subjects (62 children aged 5-8 years and 12 adults), we tested the widely-held belief that visual sensitivity improves substantially during childhood. Maturation of the retino-striate pathways is generally invoked to account for age-related changes in visual sensitivity. We evaluated the extent to which attentional factors unduly emphasized the effect of age on the purely physiological mechanisms. After a specially-designed familiarization procedure, sensitivity was fully evaluated at two locations in the superior temporal field using a bracketing technique (Octopus 2000R). False-positive (FP) and false-negative (FN) catch-trials were interspersed with the sequence of stimuli. Analyses demonstrated that: (1) age affected sensitivity; and (2) the general level of attentiveness varied not only with age, but also among subjects in the same age group. We then estimated the extent to which improved visual sensitivity may reflect a concomitant evolution of vigilance. Firstly, controlled variance analyses indicated that factors for evaluating attentiveness (rate of FN responses, slope of the psychometric function at the median, and goodness of fit) were indeed much better predictors than age of the sensitivity measured. Secondly and more significantly, the grouping of subjects into homogeneous subgroups, on the basis of their attentional performance, showed that children as young as 5 years may have a visual sensitivity that is only marginally lower than that of adults.

Adult↗

PubMed1999

Full text reading with a central scotoma: pseudo regressions and pseudo line losses.

AIMS: To investigate the reading strategy of a patient with central scotoma, using several preferred retinal loci (PRL). METHODS: A 47 year old man with Stargardt's disease was asked to decipher texts projected onto his retina using a scanning laser ophthalmoscope. A recording of the fundus image, on which the projected texts were superimposed, was analysed frame by frame. RESULTS: The subject used a combination of three PRL, located above the scotoma and laterally to the left and right of it. He first used his left PRL to search for the beginning of a line, then switched to his right PRL, thus performing an apparent regression which was called "pseudo regression", to read the line with successive rightward saccades. To decipher a particularly difficult word, he switched to his upper PRL, showing an apparent line loss which was called ("pseudo line loss"), and then used his three PRL in combination. CONCLUSION: The patient used a complex, well structured reading strategy. These data showed that backward saccades and unexpected line losses, hitherto thought to be inappropriate and uneconomical, may in fact represent purposeful changes of PRL. It is thought that this is the first structured reading behaviour ever identified in such a condition. Such adaptive oculomotor behaviour should be taken into account when considering rehabilitation procedures.

Eye Movements↗

PubMed1998

Automated visual field examination in children aged 5-8 years. Part I: Experimental validation of a testing procedure.

In 106 children aged 5-8 years, we determined how much training was needed to stabilize the response strategy prior to actual visual field assessment and we evaluated the reliability and acceptable duration of automated static perimetry (Octopus 2000R). A specially designed familiarization procedure was used to train the children to: (1) gaze at the center of the visual field while paying attention to light stimuli projected onto the periphery and (2) press the buzzer only when light stimuli were perceived. The subsequent examination phase consisted of 15 successive identical blocks of 27 trials (12 stimulus trials, 12 false-positive catch-trials, and three false-negative catch-trials), and was stopped before the end if signs of fatigue appeared. Age had a marked influence both on endurance (the number of blocks performed increased significantly) and on response reliability (false-positive responses decreased between 5- and 6-year-olds). The increase in false-negative responses toward the end indicates that examination is no longer reliable, and should be stopped. We concluded that most children as young as five can undergo examination by automated static perimetry. Changes regarding learning, stimulus intensity and testing procedure are suggested in order to adapt the examination to age, level of vigilance and health condition of the children.

Age Factors↗

PubMed1998

Automated visual field examination in children aged 5-8 years. Part II: Normative values.

We determined normative values for the visual sensitivity threshold in 118 children aged 5-8 years, using automated static perimetry (Octopus 2000R, program 32). In addition, 17 normal adults were tested. The children first underwent a familiarization procedure. One week later, quantitative examination was performed according to a specially designed schedule divided into three phases. For each of the 76 points tested, mean thresholds and standard deviations were calculated as a function of age. In contrast to previous studies, sensitivity difference between adults and children over the central 30 degrees of the visual field emerged only for the youngest age groups (5- and 6-year olds). Both the response rate in false-negative trials, and values of a within-subject threshold variability index, suggested that 5- and 6-year-olds' higher thresholds were inflated by non physiological factors, such as vigilance and cognitive processes. For these ages, the data reported here should therefore be considered as an approximation of the upper level of the thresholds. In contrast, our results for 7- and 8 year-old children provided reliable normative values for light sensitivity across the visual field.

Adult↗

PubMed1996

Feasibility of automated visual field examination in children between 5 and 8 years of age.

AIMS: To investigate how young children develop the ability to undergo a visual field evaluation using regular automated perimetry. METHODS: The study included 42 normal girls aged 5, 6, 7, and 8 years. Twelve locations in the 15 degrees eccentricity were tested in one eye, using an Octopus 2000R perimeter with a two level strategy. False positive and false negative catch trials were presented. The examination was performed three times in succession. Before the examination procedure, a specially designed programme was conducted for progressive familiarisation. RESULTS: During the familiarisation procedure, it was found that all of the 5-year-old children, seven of the 6-year-old children, and three of the 7-year-old children were unable to perform immediately, and correctly, the instructions given during the familiarisation phase; these children took from 30 seconds to 3 minutes to comply with the examiner's requests. With the exception of one 5-year-old child, all tested subjects completed the planned procedure. The mean proportion of false negative answers in catch trials was 1.6%. The mean proportion of false positive answers was 12.2%. The quadratic dependency on age suggested by the averages was not significant (F(3,116) = 0.88; p = 0.45). Detection stimulus improved with age, as shown by the fact that probability of perceiving dim stimulus increases significantly (F(3,116) = 12.68; p < 0.0001). CONCLUSION: Children did remarkably well regarding both the duration of the examination and the reliability of the answers. A preliminary familiarisation phase with a specially designed adaptation programme was found to be mandatory with children aged 7 or under. To our knowledge, this is the first time that such an investigation has been performed.

Age Factors↗

PubMed1995

[Automated static perimetry in the child: methodologic and practical problems].

PURPOSE: In a pediatric population, the use of computerized static perimetry is known as particularly difficult. The specific difficulties which may occur when testing young subjects are stability of fixation, ability to maintain concentration, resistance throughout the procedure, and reliability of the answers. It seems important to investigate and to develop appropriate strategies for the examination of children aged 8 years and younger according to their ability to undergo visual field evaluation using automated static perimetry. PATIENTS AND METHODS: Eighty normal children aged 5 to 8 years old were evaluated using an Octopus 2000R perimeter, with a one-level strategy. Adaptation of the procedure were included. RESULTS: The analysis of answers and false-positive catch-trials showed that children as young as five years old did remarkably well regarding both the duration of the examination and the reliability of answers. CONCLUSIONS: Automated static perimetry examination can provide reliable results in children as young as five years old once a familiarization procedure has been conducted and if the duration of examination does not exceed the child's capacity to remain task focused.

Child↗

PubMed1995

Angioscotomata and morphological features of related vessels in automated perimetry.

AIMS: To determine principles which regulate the occurrence of angioscotomata in automated static perimetry, variations in light sensitivity were correlated with the location and diameter of neighbouring retinal vessels. METHODS: Ten normal eyes were tested with the Octopus 2000R, using a 0.431 degree light stimulus. Sensitivity was quantified in points located around the blind spot, according to a regular, 0.5 degree constant, grid pattern. From 336 to 443 locations were tested in each eye. The resulting printouts were superimposed on corresponding fundus photographs. At each tested point, the following five additional variables were evaluated: the diameters of the closest and the second closest vessel (in 0.1 degree units); the distances of the apparent location of the tested point to the closest and the second closest vessel (in 0.25 degree units); and the distance between the two closest vessels (in 0.25 degree units). Altogether, 3869 locations were tested and 23,214 values were quantified. RESULTS: The following two conditions were found to be related to a reduction in sensitivity: (1) proximity (< 0.25 degree) to a large vessel (> or = 0.5 degree in diameter); (2) proximity (< 0.25 degree) to one of two adjacent (< 0.5 degree distant), moderately large vessels (0.3 degree to 0.4 degree in diameter). In condition 1, sensitivity was 51.3% and specificity was 92.2%; in condition 2, sensitivity was 16.2% and specificity was 98.3%; and with a combination of conditions 1 and 2, sensitivity was 67.6% and specificity was 90.5%. Increase by 0.1 degree of an adjacent vessel which was 0.4 degree in diameter markedly affected light sensitivity. CONCLUSION: Modifications in vessel diameter are observed in a number of circumstances, including adaptive vascular response to changes in ambient conditions and obstructive disorders of retinal vessels. These findings indicate that changes in vessel diameter over time can result in fluctuation of sensitivity. It is concluded that, in contrast with what is commonly stated, when ocular media are unaltered and the subject's collaboration is adequate, temporal variations in measured thresholds do not necessarily reflect functional changes in nervous tissues in the visual pathways.

Adult↗

PubMed1990

[The Gray Scale of the Octopus N1 perimetry analysis program in neuro-ophthalmology].

The gray scale of the Octopus neuro-ophthalmologic program N1 shows the difference between actual values and age-related normality. This permits optimal visualization of slight relative scotomas. The interpolation algorithm is computed for the four individual quadrants of the visual field, enabling either lateral hemianopic or fascicular defects to be sharply delineated. In addition, the N1 program automatically provides a global, nonsectorial gray scale which is useful for demonstrating visual defects which are not delineated by either the horizontal or the vertical meridian.

Algorithms↗