Spatial and temporal aspects of visual performance in relation to light level and normal aging

The research contained in this thesis describes three studies designed to investigate the ability of the observer to detect stimuli defined by changes in luminance in space and/or time in mesopic conditions, including contrast sensitivity, temporal flicker sensitivity and visual acuity. The first two studies determined the effect of the aging of the retina on spatial and temporal contrast sensitivity at photopic and mesopic light levels. The literature states that older people experience losses of retinal neurons including rods, cones and ganglion cells. Furthermore, older people tend to have particular difficulties with vision at low light levels which can be attributed to greater loss of rods than cones, particularly at parafoveal eccentricities. Spatial and temporal contrast sensitivity was measured separately in two groups of participants, aged 20-73 (n=74) and 20-74 (n=80) years of age, respectively. Measures were taken to ensure that thresholds largely reflected age-related changes to the retina rather than the optics of the eye. Spectral content of the stimuli was restricted to the middle and long wavelength regions of the visual spectrum and the pupil was measured continuously so as to obtain participant-specific retinal illuminances for each condition. The HRindex was derived and calculated for each participant as a single number which summarized performance from photopic to mesopic light levels. As age increased both spatial and temporal contrast vision worsened and older participants showed particularly elevated thresholds at lower light levels when compared to younger participants. Spatial contrast thresholds show a steady linear decline with age, whereas temporal modulation thresholds were relatively stable up to 50 years of age and then demonstrated a rapid decline. These different trends of changes in performance with increasing age suggests that contrast and temporal HRindex may be measuring the aging of different retinal mechanisms. The normal limits of HRindex values were calculated which could be used in the future to detect abnormal performance. A secondary aim of the first two studies was to determine if binocular summation of spatial and temporal contrast thresholds declined with age, while accounting for differences in retinal illuminance between monocular and binocular conditions. For spatial contrast vision, binocular summation declined significantly with age and 18% showed binocular inhibition. However, the binocular summation of flicker signals did not change significantly with age and only 1% of participants showed binocular inhibition. Interocular differences cannot explain our results. The third study determined whether altering the scotopic/photopic luminous efficiency ratio could improve spatial acuity at mesopic light levels. This was achieved by altering the spectral power distribution of illuminating lights to increase the contribution of rods to vision at constant levels of photopic illumination. It was found that visual acuity at the fovea was improved by low levels of increased scotopic luminance, but peripheral acuity was improved by larger increases of scotopic luminance. The three studies demonstrate that the detection of luminance defined stimuli can be compromised in a number of external conditions such as low light levels, as well as due to internal changes caused by aging to the optics of the eye, retina and/or the central visual system

Micro-costing the provision of emotional support and information in UK eye clinics

Sight loss has wide ranging implications for an individual in terms of education, employment, mobility and mental health. Therefore there is a need for information and support to be provided in eye clinics at the point of diagnosis of sight threatening conditions, but these aspects of care are often missing from clinics. To meet these needs, some clinics employ an Eye Clinic Liaison Officer (ECLO) but the position has yet to be widely implemented. The aims of this study were:(1) To evaluate the forms of advice and emotional support in eye clinics provided by ECLOs.(2) To determine the cost of the ECLO service per patient

Flicker Sensitivity in Normal Aging-Monocular Tests of Retinal Function at Photopic and Mesopic Light Levels

Purpose: Aging can affect many aspects of visual performance. In general, the effects become more significant in those older than 40 to 50 years, with increased intersubject variability and stronger dependence on ambient illumination. This study aimed to establish how healthy aging of the retina affects the detection of 15-Hz flicker under photopic and mesopic lighting. Methods: We investigated 71 participants aged 20 to 75 years. Thresholds were measured for detection of 15-Hz flicker at the fovea (0°) and at an eccentricity of 4° in each of the four quadrants. The background luminance ranged from 0.6 to 60 cd/m2 and pupil size was measured continuously. Participants were excluded if they had signs/history of ocular disease, substantial interocular differences in flicker thresholds, or were unable to detect 100% flicker modulation in the high mesopic range. Results: Mesopic and photopic flicker thresholds were used to calculate an index, the health of the retina index, to determine the limits of flicker sensitivity in healthy aging. Log flicker thresholds changed bilinearly with age; they remained stable until 40 to 50 years, with a linear decline with increasing age. This bilinear pattern of the change in flicker thresholds with age is consistent across photopic and mesopic light levels. Conclusions: The health of the retina index captures the lowest threshold, usually obtained under photopic conditions, as well as the loss of flicker sensitivity with decreasing light level. The established limits of healthy aging may benefit from future studies in patients with ocular hypertension and/or glaucoma that are known to experience loss of flicker sensitivity

Capturing age-related changes in functional contrast sensitivity with decreasing light levels in monocular and binocular vision

Purpose: It is challenging to separate the effects of normal aging of the retina and visual pathways independently from optical factors, decreased retinal illuminance and early stage disease. This study determined limits to describe the effect of light level on normal, age-related changes in monocular and binocular functional contrast sensitivity. Methods: 95 participants aged 20 to 85 were recruited. Contrast thresholds for correct orientation discrimination of the gap in a Landolt C optotype were measured using a 4 four-alternative, forced-choice (4AFC) procedure at screen luminances from 34 to 0.12 cd/m2, at the fovea and parafovea (0° and ±4°). Pupil size was measured continuously. The Health of the Retina index (HRindex) was computed to capture the loss of contrast sensitivity with decreasing light level. Participants were excluded if they exhibited performance outside the normal limits of interocular differences or HRindex values, or signs of ocular disease. Results: Parafoveal contrast thresholds showed a steeper decline and higher correlation with age at the parafovea than the fovea. 83% of participants with clinical signs of ocular disease had HRindex values outside the normal limits. Binocular summation of contrast signals declined with age, independent of interocular differences. Conclusion: The HRindex worsens more rapidly with age at the parafovea, consistent with histological findings of rod loss and its link to age-related degenerative disease of the retina. The HRindex, and interocular differences could be used to screen for and separate the earliest stages of sub-clinical disease from changes caused by normal aging

Evaluation of an Emotional Support Service for the Visually Impaired

Purpose. To evaluate the impact of a facilitated peer group emotional support service on visual quality of life (VQoL). Methods. Consecutive participants in an emotional support service delivered to groups of up to 6 and facilitated by trained counsellors were recruited (n=29). The VCM1 instrument was administered to participants at the start of the service, at the end of the service, and 6 months after completion of the service. Results. For the group as a whole, VQoL significantly improved between the beginning of the service and the end (F(1, 23) =16.43, p=.000), but was no better than at the start six months later (F(1,23)=3.60, p=.07). However, those with poorer initial VQoL showed significantly greater improvements after six months (1.74±2.21 logits) than those with higher initial VQoL (-0.12±0.71 logits) (t(23)=2.89, p=.008). The effect size of the intervention for those with poor initial VQoL was 1.10 at the end of service, and 0.92 after six months. The items which became and remained easier were feeling lonely or isolated due to eyesight, feeling sad or low due to eyesight, and feeling worried about general safety outside the home. Conclusions. This facilitated peer group emotional support service significantly improves VQoL as assessed with the VCM1 over at least 6 months for those with poorer initial VQoL. Different interventions may be needed for those with initially good VQoL, and to improve other aspects of quality of life not influenced by the service