The relative loss of chromatic and achromatic sensitivity in primary open angle glaucoma and the normal ageing process

Primary open angle glaucoma is a progressive and relatively common disease. Damage to the retinal ganglion cells causes characteristic structural changes in the optic nerve head, progressive loss of visual function and eventually blindness. Early detection of this disease is therefore desirable. It has been suggested that the assessment of impaired visual function in glaucoma can be made more sensitive by the selective isolation of specific stimulus attributes. An important aim of this investigation was to establish how the processing of colour or luminance contrast signals is affected differently in glaucoma. Chromatic sensitivity was measured using a computerised colour display that employs isoluminant colour-defined stimuli buried in dynamic luminance contrast noise, stimulus conditions that isolate the use of colour signals and reveal loss of chromatic sensitivity. The characterisation of chromatic sensitivity loss in a group of POAG and at risk subjects was determined by measuring chromatic displacement (CD) thresholds along 12 directions in CIE - xy chromaticity chart, which allowed fitting CD ellipses. The analysis of the pattern of CD loss at different stages of the disease, both at the fovea and 7 deg, reveals the earliest signs of damage to be found at the paracentral location (7 deg). A non-selective CD loss with a characteristic increase in variance is observed early in the disease. As damage progresses foveal sensitivity is also progressively affected showing a greater B/Y relative loss, which becomes similar and even exceeded by the R/G loss when the disease is established. For moderate and advanced stages of the disease, the relative loss becomes greater for the R/G thresholds at both foveal and 7 deg. The test showed an overall success rate of 71% in identifying cases correctly. In addition, moving, colour-defined stimuli designed to isolate either the transient luminance channel or the R/G and B/Y chromatic colour opponent mechanisms were used to find evidence of preferential damage for detection of one or the other of these stimulus attributes. Findings in patients with POAG and normal subjects of similar and younger age were compared. The relative increase of chromatic (R/G and B/Y) and achromatic thresholds was determined with ageing and glaucomatous damage. Although both mechanisms were significantly affected by POAG damage, the chromatic thresholds showed greater relative increase. The R/G and B/Y chromatic thresholds increased differently as a function of the severity of visual field loss. The B/Y sensitivity showed the greatest loss in early glaucoma subjects, however the R/G mechanism showed a faster rate of threshold increase and a better correlation with severity of field loss than B/Y thresholds. Ageing affected significantly both the chromatic (R/G and B/Y) and achromatic mechanisms. Chromatic threshold increases were on average twice the increase observed in the achromatic mechanism for foveal and parafoveal measurements. The rate of increase, as a function of age, in chromatic thresholds (along R/G and B/Y mechanisms) showed an accelerated fashion from the 5th-6th decade onwards. Meanwhile the achromatic thresholds increased at a slower, linear rate throughout life. In spite of the initial, more rapid increase along the B/Y colour opponent system (particularly for foveal thresholds), there were no significant differences between the rate of ageing for R/G and B/Y mechanisms. The largest age-related loss of chromatic sensitivity occurs in the lower hemifield for the B/Y mechanism. In conclusion, both the glaucomatous damage and the ageing process lead to reduction in both R/G and B/Y chromatic sensitivity. The relative B/Y versus R/G chromatic loss in POAG depends on the severity of glaucomatous damage. The first signs of chromatic discrimination loss in the patients at risk of suffering POAG appear in the paracentral locations (7 deg) and are characterised by a non-selective loss of chromatic sensitivity and an increased inter- and within- subject variability. The relative age-related loss of R/G and B/Y sensitivity is mostly non- selective and independent of stimulus location

Eye movements during visual search in patients with glaucoma

Background: Glaucoma has been shown to lead to disability in many daily tasks including visual search. This study aims to determine whether the saccadic eye movements of people with glaucoma differ from those of people with normal vision, and to investigate the association between eye movements and impaired visual search. Methods: Forty patients (mean age: 67 [SD: 9] years) with a range of glaucomatous visual field (VF) defects in both eyes (mean best eye mean deviation [MD]: –5.9 (SD: 5.4) dB) and 40 age-related people with normal vision (mean age: 66 [SD: 10] years) were timed as they searched for a series of target objects in computer displayed photographs of real world scenes. Eye movements were simultaneously recorded using an eye tracker. Average number of saccades per second, average saccade amplitude and average search duration across trials were recorded. These response variables were compared with measurements of VF and contrast sensitivity. Results: The average rate of saccades made by the patient group was significantly smaller than the number made by controls during the visual search task (P = 0.02; mean reduction of 5.6% (95% CI: 0.1 to 10.4%). There was no difference in average saccade amplitude between the patients and the controls (P = 0.09). Average number of saccades was weakly correlated with aspects of visual function, with patients with worse contrast sensitivity (PR logCS; Spearman’s rho: 0.42; P = 0.006) and more severe VF defects (best eye MD; Spearman’s rho: 0.34; P = 0.037) tending to make less eye movements during the task. Average detection time in the search task was associated with the average rate of saccades in the patient group (Spearman’s rho = −0.65; P < 0.001) but this was not apparent in the controls. Conclusions: The average rate of saccades made during visual search by this group of patients was fewer than those made by people with normal vision of a similar average age. There was wide variability in saccade rate in the patients but there was an association between an increase in this measure and better performance in the search task. Assessment of eye movements in individuals with glaucoma might provide insight into the functional deficits of the disease

Relationship between visual field loss and contrast threshold elevation in glaucoma

BACKGROUND: There is a considerable body of literature which indicates that contrast thresholds for the detection of sinusoidal grating patterns are abnormally high in glaucoma, though just how these elevations are related to the location of visual field loss remains unknown. Our aim, therefore, has been to determine the relationship between contrast threshold elevation and visual field loss in corresponding regions of the peripheral visual field in glaucoma patients. METHODS: Contrast thresholds were measured in arcuate regions of the superior, inferior, nasal and temporal visual field in response to laser interference fringes presented in the Maxwellian view. The display consisted of vertical green stationary laser interference fringes of spatial frequency 1.0 c deg(-1 )which appeared in a rotatable viewing area in the form of a truncated quadrant extending from 10 to 20° from fixation which was marked with a central fixation light. Results were obtained from 36 normal control subjects in order to provide a normal reference for 21 glaucoma patients and 5 OHT (ocular hypertensive) patients for whom full clinical data, including Friedmann visual fields, had been obtained. RESULTS: Abnormally high contrast thresholds were identified in 20 out of 21 glaucoma patients and in 2 out of 5 OHT patients when compared with the 95% upper prediction limit for normal values from one eye of the 36 normal age-matched control subjects. Additionally, inter-ocular differences in contrast threshold were also abnormally high in 18 out of 20 glaucoma patients who had vision in both eyes compared with the 95% upper prediction limit. Correspondence between abnormally high contrast thresholds and visual field loss in the truncated quadrants was significant in 5 patients, borderline in 4 patients and absent in 9 patients. CONCLUSION: While the glaucoma patients tested in our study invariably had abnormally high contrast thresholds in one or more of the truncated quadrants in at least one eye, reasonable correspondence with the location of the visual field loss only occurred in half the patients studied. Hence, while contrast threshold elevations are indicative of glaucomatous damage to vision, they are providing a different assessment of visual function from conventional visual field tests

Optometría : manual de exámenes clínicos

Este texto de exámenes clínicos optométricos ha sido desarrollado en forma de manual para poder ser consultado de forma rápida y sencilla durante la práctica de la optometría. Asimismo, también puede servir de guía para aquellos que se inician en esta profesión.2a e

Visión binocular : diagnóstico y tratamiento

Este libro está dirigido a todos los profesionales del campo de la optometría que quieran profundizar en la visión binocular. También está indicado para los alumnos de tercer curso de Optometría, tanto en asignaturas troncales como optativas. Sus contenidos están divididos en capítulos que pueden ser leídos de forma independiente, aunque es recomendable comprender el presente texto como una unidad. Su estructura abarca desde las disfunciones binoculares más frecuentes al estrabismo, la ambliopía y la optometría pediátrica, pasando por las diversas opciones de tratamiento, incluida la terapia visual

A stacked record of relative geomagnetic paleointensity for the past 270 kyr from the western continental rise of the Antarctic Peninsula

Paleomagnetic and rock magnetic investigations were carried out on four gravity cores recovered from the western continental rise of the Antarctic Peninsula during the SEDANO II cruise of RV OGS-Explora. The studied cores, each about 6.5 m-long, were collected at a depth of 3700–4100 m below the sea level, on the distal gentle side of sediment Drift 7, and consist of very fine-grained sediments spanning through various glacial–interglacial cycles. Detailed analysis of the paleomagnetic and rock magnetic data allowed to reconstruct relative paleointensity (RPI) records (NRM20 mT/ARM20 mT) for each core.We established a refined age model for the studied sequences by correlating individual SEDANO RPI curves to the global RPI stack SINT-800 [Y. Guyodo, J.-P. Valet, Global changes in intensity of the Earth's magnetic field during the past 800 kyr, Nature 399 (1999) 249–252]. The individual normalized SEDANO RPI records are in mutual close agreement; they were thus merged in a RPI stacking curve spanning the last 270 kyr and showing a low standard deviation. This study also points out that RPI records may provide a viable tool to date otherwise difficult-to-date sedimentary sequences, such as those deposited along peri-Antarctic margins. The new RPI chronology indicates that the sampled sedimentary sequence is younger than previously thought and allows a new high-resolution correlation to oxygen isotope stages. Furthermore, we recognized variations in the rock magnetic parameters that appear to be climatically-driven, with changes in the relative proportion of two magnetic mineral populations with distinct coercivities. Rock magnetic and lithological trends observed in the SEDANO cores indicate that during the climatic cycles of the Late Pleistocene this sector of the peri-Antarctic margin was subjected to subtle, yet identifiable, environmental changes, confirming a relatively higher instability of theWest Antarctic ice sheet with respect to the East Antarctic counterpart