Gaze and pupil changes during navigation in age-related macular degeneration.

BACKGROUND: The central visual field is particularly affected in age-related macular degeneration (AMD), and this can impinge on a variety of functional tasks, including navigation, which can affect activities of daily living. It has been difficult to assess navigational function under standardised conditions. The aim of this study is to examine gaze function and pupil diameter during navigation in patients with AMD. METHODS: This study was designed as an observational case-control investigation. 34 patients with AMD and 23 controls were recruited. We simulated a walking journey using video projection and monitored patients using automated eye tracking. Visual acuity, fixation count, fixation duration and pupil diameter were recorded while subjective measurements included recorded voice comments. RESULTS: The pupil diameters were significantly greater in the AMD group compared with the control group in both easy and difficult segments of navigation (p=0.002). Fixation counts were significantly higher in the AMD group during difficult segments of navigation (p=0.001). The differences in both pupil diameter and fixation count correlated with subject visual acuity. CONCLUSIONS: Fixation count is a marker of difficult navigational environments in patients with AMD. The combination of video projection and eye tracking to assess visual navigation function is a useful clinical tool and an adjunct to current investigation tools in AMD intervention studies providing objective clinical measures under standardised settings.

Quality of life and relative importance: a comparison of time trade-off and conjoint analysis methods in patients with age-related macular degeneration.

AIM: To investigate the relative priorities in quality of life (QoL) in patients with age-related macular degeneration (AMD). METHODS: Measures of visual function, QoL and utility associated with visual loss were obtained from 122 patients with AMD classified according to macular morphology. The two methods of utility assessment were time trade-off (TTO) and conjoint analysis (CA), which have been recommended by the UK's National Institute of Clinical Excellence as techniques for the assessment of healthcare priorities. RESULTS: Results show that the two methods for assessing utility are poorly related: TTO relates moderately to visual function and disease severity but CA does not. CA identified two different subgroups of patients: one with outdoor mobility and the other with reading as their main priority. CONCLUSION: Further work is needed and caution required in interpreting data obtained using these methodologies for determining their relative importance in vision-related QoL studies.

A prospective study of visual function and quality of life following PDT in patients with wet age related macular degeneration.

AIMS: (1) A prospective study to assess visual function measures and quality of life (QoL) in patients with wet age related macular degeneration (AMD) treated with photodynamic therapy (PDT). (2) To assess if PDT prevents severe visual loss (loss of six or more lines of distance visual acuity) in the treated eye. METHODS: 48 of 51 recruited patients with predominantly classic subfoveal choroidal neovascularisation (CNV) secondary AMD who were treated with PDT were followed up for 1 year. Assessment included distance and near visual acuity, contrast sensitivity, vision related quality of life and fluorescein angiography. Photodynamic therapy using Visudyne was carried out according to standard protocol. Patients were followed up every 3 months and treatment repeated if there was significant leakage from CNV. RESULTS: At the 12 month follow up, 71% (n = 34) of the patients lost less than three lines of best corrected distance visual acuity. Although there were significant decreases in some of the QoL items tested, patients were significantly less anxious and more independent outdoors at the 12 month follow up. CONCLUSION: This study is in keeping with published literature with PDT preventing severe visual loss in two thirds of treated patients with predominantly classic CNV.

Retention of corneal epithelial cells following Goldmann tonometry: implications for CJD risk.

AIMS: To assess the adequacy of current decontamination methods for the Goldmann tonometer in the context of variant Creutzfeldt-Jakob disease (vCJD). METHODS: Reusable Goldmann tonometer prisms were used to perform applanation tonometry on different groups of patients. Following tonometry, retained materials were collected from the tonometer prism head and examined using cytological methods. The used tonometers were subjected to a series of conditions to evaluate their effect on the residual cell numbers found on the tonometer heads. These included wiping alone and wiping or washing followed by disinfection of the tonometer prism. The effect on cell counts of drying the prism overnight was studied, as well as drying overnight and then wiping and disinfecting. All disinfections were performed with sodium hypochlorite (0.05% w/v). RESULTS: The cytology specimens of 69 patients were studied. Patients using eye drops regularly desquamated significantly more corneal epithelial cells with Goldmann tonometry than patients not using regular eye drops. The mean number of cells was 156 (range 0-470) for patients using eye drops and 14 (4-57) for patients not using eye drops (p = 0.004). Wiping or washing the tonometer head reduced the cell number significantly but neither method completely eliminated cells. The two methods were not significantly different (p=0.3). Drying left a large number of cells (23-320 cells). CONCLUSIONS: Retained corneal epithelial cells, following the standard decontamination routine of tonometer prisms, may represent potential prion infectivity. Manual cleaning was the most important step in reducing epithelial cell retention.

Visual function in multiple sclerosis.

126 patients with multiple sclerosis and normal visual acuity were submitted to a battery of tests of visual function. The investigation included visual evoked potential, contrast sensitivity by three methods, and a segment of the Farnsworth-Munsell 100 Hue test. 22 of the patients gave a history of unilateral acute optic neuritis and in these the abnormalities were greater in degree. Contrast sensitivity emerged as the most useful test and was abnormal in 92.2% of eyes. Visual evoked potential was delayed in 35.6% and colour vision was abnormal in less than a third. In general, contrast sensitivity was depressed at all frequencies and most of the abnormalities could be identified by testing at a single frequency of 4 cycles/degree.

The clinical significance of change.

Clinicians frequently make judgements about the clinical importance of a change in "score" on visual function tests obtained from patients on successive visits. Almost no normative data for assessing the significance of change in performance on routinely used clinical tests exists, and the importance of collecting such data is emphasized. A description of how normative data for the significance of change can be collected is given, using the Farnsworth-Munsell 100 hue test as an example. Although there are always limitations to estimates of error variance, the importance of determining the precision of clinical tests, for guiding rational decision making, is stressed.

Clinical inferences and decisions--III. Utility assessment and the Bayesian decision model.

It is accepted that errors of misclassifications, however small, can occur in clinical decisions but it cannot be assumed that the importance associated with false positive errors is the same as that for false negatives. The relative importance of these two types of error is frequently implied by a decision maker in the different weighting factors or utilities he assigns to the alternative consequences of his decisions. Formal procedures are available by which it is possible to make explicit in numerical form the value or worth of the outcome of a decision process. The two principal methods are described for generating utilities as associated with clinical decisions. The concept and application of utility is then expanded from a unidimensional to a multidimensional problem where, for example, one variable may be state of health and another monetary assets. When combined with the principles of subjective probability and test criterion selection outlined in Parts I and II of this series, the consequent use of utilities completes the framework upon which the general Bayesian model of clinical decision making is based. The five main stages in this general decision making model are described and applications of the model are illustrated with clinical examples from the field of ophthalmology. These include examples for unidimensional and multidimensional problems which are worked through in detail to illustrate both the principles and methodology involved in a rationalized normative model of clinical decision making behaviour.

Prediction of diabetic retinopathy from clinical variables and color vision data.

Predictions about the onset of retinopathy in 295 diabetic patients, all originally having no evidence of retinopathy, have been made in a longitudinal study over 7 yr. Out of many color vision tests and clinical variables, the best individual predictor was a measure of yellow-blue discrimination, using an anomaloscope. The other predictors of significance were the degree of blood glucose control and the duration of diabetes. Although the predictions from a linear logistic model were significant in classifying the diabetic subjects into those whose fundus will remain normal and those in whom it will develop retinopathy, the number of misclassifications was substantial. An examination of the goodness of fit between the data and the model suggested a criterion value (P) of around P = 0.3 for the probability that a patient develops retinopathy. At this value, the probability of being normal for an individual classed as normal was 0.82, and the probability of developing retinopathy for an individual classed as having retinopathy was 0.54.

Rod-cone interaction: some indirect evidence.

A group of diabetic patients were found to have losses in green-blue colour discrimination and significantly early transition times in dark adaptation. Analysis showed that the green-blue losses were significantly related to early transition time. Pre-receptoral factors cannot account for these results but selective degeneration of the blue cone mechanism can. The results are in agreement with a proposal of rod-blue cone linkage after Trezona (1970).

Peripheral vision in children.

A comparison of peripheral vision in adults and children showed that children had reduced sensitivity in a standard visual field examination. The constriction of the visual field amounted to 0.4 log units at 30 degrees excentricity in a static perimetric test. This loss was maintained in a spatial forced choice experiment without foreknowledge of target location. However, in a temporal forced choice experiment with foreknowledge of target position the difference between children and adults was reduced to 0.1 log units. It is thought, therefore, that the former visual loss in children is due to the nature of the task rather than to deficiencies in the visual mechanisms.