The charge exchange recombination spectroscopy diagnostic on the upgraded Lithium Tokamak eXperiment (LTX-ß).

The Lithium Tokamak eXperiment has undergone an upgrade to LTX-ß, a major part of which is the addition of neutral beam injection (NBI). NBI has allowed for a new charge exchange recombination spectroscopy (CHERS) system to be installed in order to measure impurity concentrations, ion temperature, and toroidal velocity. Previously on LTX measuring these parameters relied on passive spectroscopy and inversion techniques and had large uncertainty. The CHERS system has 52 total views, split into four groups of 13, half facing toward the beam and half symmetrically facing away from the beam, so the background non-beam related emission can be simultaneously subtracted. Both sets of views sample a major radius of 27-59 cm, with resolution through the beam of 1.5-2.5 cm. LTX-ß is expected to have its magnetic axis near 35 cm, with minor radii of 18-23 cm. Three separate spectrometers will be used for the diagnostic, giving the system great flexibility to simultaneously measure emission from multiple impurity lines. The viewing optics are f/1.8, allowing all of the spectrometers to be fully illuminated. Design and calibration of the system as well as the advantages of various configurations of the spectrometers will be highlighted.

Assessing the reliability, discriminative ability, and validity of disability glare tests.

PURPOSE: To gather information regarding the reliability, discriminative ability, and validity of disability glare tests. METHODS: The following glare tests were evaluated: the Miller-Nadler, Vistech MCT8000, Berkeley, van den Berg Straylightmeter, and the Brightness Acuity Tester used with the Pelli-Robson and Regan charts. Three test evaluation criteria were used: (1) repeatability--comparing test scores on two visits; (2) discriminative ability--the tests' ability to differentiate between young and old subjects and between old normal and cataract subjects; (3) validity--comparing cataract test scores with the reference standard of the van den Berg Straylightmeter. Three subject groups were evaluated: young normals (n = 24, mean age 24.3 +/- 3.3 yr), older normals (n = 22, mean age 66.0 +/- 6.2 yr), and early cataract (n = 33, mean age 70.6 +/- 8.1 yr). RESULTS AND CONCLUSIONS: Data indicate that contrast sensitivity or low contrast acuity measured in the presence of glare are superior to disability glare scores in assessing cataract patients with normal neural function. Under glare conditions, contrast sensitivity and low contrast acuity scores from the Pelli-Robson, Regan, and Berkeley tests provide similarly reliable, discriminative, and valid measures of visual assessment in cataract. The Miller-Nadler glare tester poorly detects and measures subtle changes in the ocular media, such as early cataract, because of its large step sizes at low contrast thresholds. The poor reliability of the Vistech MCT8000 limits its usefulness. The study suggests that unless good chart design and psychophysics are used, the geometry and intensity of the glare source are of little importance.

Confirmation of the validity of the psychophysical light scattering factor.

PURPOSE: To reevaluate the validity of the light scatter factor (LSF) formula of Paulsson and Sjöstrand, LSF = L/E (M2/M1-1), where L is the target luminance, E is the illuminance of the glare source at the eye, and M2 and M1 are modulation contrast thresholds measured with and without the glare source, respectively. This equation has recently been deemed invalid by Yager, Yuan, and Mathews. METHOD: Ratios of contrast thresholds with and without glare were measured for three glare illuminance levels for each of three stimulus luminances. This results in five different ratios of L/E, spanning a range of 1.60 log units. RESULTS: The data show an excellent fit to the Paulsson and Sjöstrand equation, and the LSF scores conform well to previously published normative values. CONCLUSION: The light scatter factor equation of Paulsson and Sjöstrand is confirmed as valid without resorting to the need for correction factors based on variables such as pupil size.

Development of a reading speed test for potential-vision measurements.

PURPOSE: Previous studies suggest that optimal reading speed is unaffected by cataract, yet is significantly reduced in age-related macular degeneration (ARMD ). This raises the question of whether a reading speed test could be developed to assess potential vision after cataract surgery. METHODS: Nineteen subjects with cataract, 15 with ARMD, and 13 control subjects with normal, healthy eyes read Bailey-Lovie word charts aloud, and subsequently, critical print size and optimal reading speed were calculated. Measurements were also taken with the charts in reversed-contrast polarity and after pupillary dilation. RESULTS: Although the subjects with cataract had reduced word acuity and increased critical print size, optimal reading speed was similar to that of the control group at a mean of approximately 100 wpm. Optimal reading speed in the subjects with ARMD was substantially worse (mean of 39 wpm). Reversing the contrast polarity of the charts slightly increased the word acuity and optimal reading speed of the subjects with cataract. CONCLUSIONS: The results suggest that optimal reading speed would be useful as a potential-vision test. The proposed test would use text size of at least 1.32 degrees (1.2 log minimum angle of resolution [logMAR]), and pupil dilation would be unnecessary. A reading test with black letters on a white background would be adequate, because charts with reversed-contrast polarity made minimal difference in reading speed.

Factors affecting light-adapted pupil size in normal human subjects.

PURPOSE: To investigate the effect of age, gender, refractive error, and iris color on light-adapted pupil size in humans. METHODS: Pupil diameters of 91 subjects (age range, 17 to 83 years) with normal, healthy eyes were measured using an objective infrared-based continuous recording technique. Five photopic ocular illuminance levels were used (2.15 to 1050 lumens m-2), and the accommodative status of each subject was precisely controlled at a constant level. RESULTS: Pupil size decreased linearly as a function of age at all illuminance levels. Even at the highest illuminance level, there was still a significant effect of age upon pupil size. The rate of change of pupil diameter with age decreased from 0.043 mm per year at the lowest illuminance level to 0.015 mm per year at the highest. In addition, the variability between pupil sizes of subjects of the same age decreased by a factor of approximately two as luminance was increased over the range investigated. Pupil size was found to be independent of gender, refractive error, or iris color (P > 0.1). CONCLUSIONS: Of the factors investigated, only chronologic age had a significant effect on the size of the pupil. The phenomenon of senile miosis is present over a wide range of ocular illuminance levels.

Magnification perimetry.

PURPOSE: The authors used a method of spatial scaling to quantify the eccentricity-related decline in differential light sensitivity as a function of visual field meridian and age. METHODS: Differential light threshold at the fovea was measured in two groups of subjects of differing age (young mean age, 23.6 yr; standard deviation, 2.4 yr; elderly mean age, 69.6 yr; standard deviation, 6.2 yr) using a Goldmann size I stimulus moving across fixation at 1 degree/sec. With luminance kept constant, eccentricity thresholds for kinetic stimuli of increasing magnification were then measured. The results were analyzed in terms of the E2 value, which specifies the eccentricity at which the stimulus size must double to maintain performance equivalent to that at the fovea. RESULTS: For the young subjects, eccentricity thresholds increased linearly with an increase in stimulus diameter for most meridians. E2 varied between 5-12 degrees, depending on the meridian, and showed the same meridional trend as that of retinal ganglion cell distribution, although the magnitudes of E2 were different. For the elderly subjects, the eccentricity thresholds increased in a nonlinear manner with the stimulus diameter. CONCLUSIONS: Further factors, such as spatial summation, must also determine the eccentricity dependence of the differential light threshold because ganglion cell density decreases at a much faster rate than the differential light threshold. The most marked effects of age on differential light sensitivity occur at the fovea and beyond 20 degrees in the peripheral field, with a relative sparing in the pericentral area.

Demographic characteristics of the vision-disabled elderly.

PURPOSE: To profile certain demographic features of the low-vision population in Ontario, Canada. METHODS: Sixty-six optometrists or optometry centers, 8 ophthalmologists, and 23 Canadian National Institute for the Blind rehabilitation worker teams were recruited to the study. They were required to report on their low-vision examinations during a 3-year period. RESULTS: Reports from 4744 low-vision examinations were received. Of the patients examined, 71% were over age 65 (subsequently called seniors or elderly), and 55% were over age 75. Ninety percent of all the patients lived in households and 10% lived in institutions. Seniors made up 71% of the patients living in households and 88% of the patients living in institutions. Most of the seniors were women (65%), and 57% had functional limitations in addition to low vision, most commonly limitations in mobility, hearing, or agility. Age-related maculopathy was the primary diagnosis in 75% of seniors, and the most common secondary diagnosis was cataract (46%). The main objective for most elderly low-vision patients was to gain improvement in personal reading (75%). CONCLUSIONS: The vast majority of low-vision patients were elderly, the largest number being 75 to 84 years old. When older senior low-vision patients (> or = 85 years) were compared with younger seniors (65 to 74 years), the older seniors were more likely to be women, more likely to have additional functional limitations, more likely to live in an institution, and more likely to have age-related maculopathy and cataract. Whether some elderly low-vision patients may be helped by cataract surgery needs to be determined.

N100 evoked potential latency variation and startle in schizophrenia.

The contribution of evoked potential (EP) latency jitter, a measure of CNS temporal variability, on startle and EP gating defects in schizophrenic subjects has not been characterized. The amplitude of the N100/P200 EP complex (peak to trough) derived using a time-locked averaging procedure, N100 EP latency jitter derived from single trial analysis, acoustic startle response and clinical symptoms were measured in 51 schizophrenic subjects. N100 latency jitter was inversely correlated with N100/P200 EP amplitude in both cross-sectional and longitudinal analysis. Subjects with elevated EP gating ratios (>0.5) had similar latency jitter values for initial (S1) and test (S2) stimuli, while subjects with a low gating ratio (0-0.5) had a lower level of S1 latency jitter. Temporal variability thus plays a significant and complex role in previously reported sensory gating deficits in schizophrenic subjects.

Visual acuity versus letter contrast sensitivity in early cataract.

Large and small letter contrast sensitivity and visual acuity were assessed in 37 elderly eyes (mean VA -0.01 logMAR, Snellen 6/6) and their lens opacities were categorised and graded using the LOCS III system. Large letter contrast sensitivity was often not reduced in cataract from age-matched normal values and provided limited information. Small letter contrast sensitivity was shown to be a more sensitive measure of early cataract than visual acuity and large letter contrast sensitivity. Its usefulness may be limited by its strong correlation with visual acuity (r2 = 0.70), which is the standard and traditional measure of vision in cataract.

Refractive error changes in cortical, nuclear, and posterior subcapsular cataracts.

AIMS: To determine the effect of the three main morphological types of cataract on refractive error. METHODS: Data were prospectively collected from 77 subjects (age 67 (SD 8) years) with one morphological type of cataract. 34 had cortical, 21 had nuclear, and 21 had posterior subcapsular cataract. 22 subjects with clear lenses (60 (7) years) were recruited as controls. The spherical equivalent and astigmatic vector change between spectacle correction and optimal refraction were calculated. RESULTS: The cortical cataract group showed a significant astigmatic change of 0.71 (0.67) D (mean (1 SD)) compared to the control group (0.24 (0.20) D), with 24% outside the 95% confidence limit (0.63 D). The nuclear cataract group showed a significant myopic shift of -0.38 (0.60) D compared to the control group (+0.02 (0.21) D), with 52% beyond the minus 95% confidence limit (-0.39 D). CONCLUSION: A quarter of subjects with cortical cataract showed larger changes in astigmatism than subjects with clear lenses. This is probably because of the localised refractive index changes along cortical spoke opacities within the pupillary area. The well known myopic shift of nuclear cataract was also demonstrated.

Improvements in clinical and functional vision and perceived visual disability after first and second eye cataract surgery.

AIMS: To determine the improvements in clinical and functional vision and perceived visual disability after first and second eye cataract surgery. METHODS: Clinical vision (monocular and binocular high and low contrast visual acuity, contrast sensitivity, and disability glare), functional vision (face identity and expression recognition, reading speed, word acuity, and mobility orientation), and perceived visual disability (Activities of Daily Vision Scale) were measured in 25 subjects before and after uncomplicated cataract surgery (10 first eye surgery and 15 second eye surgery) and in 10 age matched controls. RESULTS: Significant improvements were found after surgery in clinical and functional vision and perceived visual disability. Greater improvements were found after first eye surgery than after second eye surgery. However, first eye surgery did not return all scores to age matched normal levels. There were significant improvements in several of the tests measured after second eye surgery, and all postoperative values were similar to those from age matched normals. CONCLUSIONS: Significant improvements in clinical, functional, and perceived vision are obtained by cataract surgery. The improvements in objective measures of functional vision found in this study support previous findings of improvements in patients' perceived functional vision. In addition, these data provide support to the necessity of second eye surgery in some patients to improve certain aspects of visual function to age matched normal levels.

Ultraviolet-induced lenticular fluorescence: intraocular straylight affecting visual function.

Ultraviolet radiation (UVR) excitation of fluorophores within the crystalline lens results in intraocular straylight. These fluorescent emissions are known to increase with age. The visual effect of this increase in fluorescent straylight has not previously been published. In this study, the visual deficit associated with UV-induced lenticular fluorescence was measured for 61 normal subjects between the ages of 21 and 80 yr of age using the Regan visual acuity charts at varying levels of contrast. UVR was shown to decrease low contrast acuity and this loss increased linearly with age.

A comparison of sampling efficiency and internal noise level in young and old subjects.

Contrast detection in different levels of external visual noise allows a given loss in contrast sensitivity to be attributed to either an increase in the internal noise of the visual system, a decrease in sampling efficiency, or both. Sampling efficiency indicates how effectively the available stimulus information is utilized by the visual system. The aim of this study is to investigate the effect of normal ageing on sampling efficiency and internal noise. Contrast thresholds for sine-wave gratings of 6 c/deg were measured in the presence of four (including zero) levels of externally added visual noise in young and older healthy observers. Results showed that sampling efficiencies were significantly lower for the older group compared to the younger, while the internal noise showed no significant change. The implications of the data for the relative contribution of the optical and neural systems on visual function loss with ageing are discussed. Our results suggest that the neural system plays a major role in the loss of contrast sensitivity with ageing in normal, healthy eyes.

Effect of a cataract simulation on clinical and real world vision.

AIMS/BACKGROUND: Many reports have indicated that some patients with cataract can retain good visual acuity but complain of significant visual problems. This is the first in a series of papers trying to determine what causes these symptoms and whether other clinical tests can predict the real world vision loss. METHODS: The effect of a cataract simulation with a similar angular distribution of light scatter as real cataract on clinical (visual acuity, contrast sensitivity, and disability glare) and real world vision (face recognition, reading speed, and mobility orientation) was investigated. RESULTS: The simulation had a relatively small effect on visual acuity (6/6 with the simulation), but much larger effects on contrast sensitivity and low contrast acuity with and without glare. The simulation had no effect on high luminance and high contrast real world tasks, such as mobility orientation in room light and optimal reading speed. A small, but significant deterioration was found for the slightly lower contrast task of face and expression recognition. However, under low luminance conditions, substantial defects in mobility orientation were obtained (despite 6/6 acuity). CONCLUSIONS: Although the relative effect of the cataract simulation on acuity and contrast tasks is not typical of the average cataract, it can be found in those cataract patients with visual problems despite good visual acuity. This corroborates the suggestion that it is large amounts of wide angle light scatter (forward and/or backward) which are at least partly responsible for visual disability in cataract patients with good visual acuity. A patient's reported visual disability may depend on the percentage of time he or she spends under low contrast and/or low luminance conditions, such as walking or reading in dim illumination, and walking or driving at night, in fog, or heavy rain.

The usefulness of Vistech and FACT contrast sensitivity charts for cataract and refractive surgery outcomes research.

AIM: To investigate the repeatability and sensitivity of two commonly used sine wave patch charts for contrast sensitivity (CS) measurement in cataract and refractive surgery outcomes. METHODS: The Vistech CS chart and its descendant, the Functional Acuity Contrast Test (FACT), were administered in three experiments: (1) Post-LASIK and age matched normal subjects; (2) Preoperative cataract surgery and age matched normal subjects; (3) Test-retest repeatability data in normal subjects. RESULTS: Contrast sensitivity was similar between post-LASIK and control groups and between the Vistech and FACT charts. The percentage of subjects one month post-LASIK achieving the maximum score across spatial frequencies (1.5, 3, 6, 12, 18 cycles per degree) were (50, 33, 13, 13, 0 respectively) for FACT, but only (0, 0, 13, 4, 0 respectively) for Vistech. A small number of cataract patients also registered the maximum score on the FACT, but up to 60% did not achieve the minimum score. Test-retest intraclass correlation coefficients varied from 0.28 to 0.64 for Vistech and 0.18 to 0.45 for FACT. Bland-Altman limits of agreement across spatial frequencies were between +/-0.30 and +/-0.85 logCS for Vistech, and +/-0.30 to +/-0.75 logCS for FACT. DISCUSSION: The Vistech was confirmed as providing poorly repeatable data. The FACT chart, likely because of a smaller step size, showed slightly better retest agreement. However, the reduced range of scores on the chart due to the smaller step size led to ceiling (post-LASIK) and floor (cataract) effects. These problems could mask subtle differences between groups of patients with near normal visual function as found post-refractive or cataract surgery. The Vistech and FACT CS charts are ill suited for refractive or cataract surgery outcomes research.

Contrast sensitivity decline with ageing: a neural or optical phenomenon?

Previous studies of contrast sensitivity changes with age have produced conflicting results. Most recent reports indicate that, with increasing age, contrast sensitivity at medium and high spatial frequencies decreases. Whether this is caused by reduced retinal illumination due to senile pupillary miosis and increased lens absorption, by the greater light scatter of the aged eye or by retinal and neural cell loss and degeneration is also in doubt. We measured the contrast sensitivity functions of 16 young (mean age 21.5 +/- 2.7 years) and 16 older (mean age 72 +/- 4.3 years) subjects with normal healthy eyes, using a modified Rodenstock retinometer and a monitor-based computer system. The former method bypasses the effects of the optical media to measure the contrast sensitivity function of the retinal and neural system alone, while the latter measures the contrast sensitivity function of the whole visual system, including media. The results show the older group to have significantly lower contrast sensitivity at medium (4 c deg-1, p less than 0.1) and high (10.6 c deg-1, p less than 0.001; 16.5 c deg-1, p less than 0.001) spatial frequencies. They also suggest that this is due primarily to retinal and neural changes with age, with optical factors having a slight effect at the highest spatial frequency only.

Evaluating visual function in cataract.

This paper reviews recent research on the evaluation of visual function in cataract. Visual impairment in cataract is principally caused by increased intraocular forward light scatter. It is assumed that visual acuity (VA) measurements assess the impact of narrow angle light scatter. This also makes the measurement of high spatial frequency contrast sensitivity (CS) unnecessary. However, VA measurements alone are an inadequate assessment of visual impairment in some patients with cataract. In addition, it is suggested that a measurement of wide-angle light scatter is required. This can be evaluated directly using the van den Berg Straylightmeter, or indirectly using low spatial frequency CS or disability glare (DG) tests. The following are discussed: (1) the relative usefulness of these tests; (2) how they can be incorporated into the decision as to when to extract a cataract; and (3) the importance of considering binocular visual function.

Management of patients with age-related cataract.

The majority of patients referred because of age-related cataract should be referred when their ability to function in their desired lifestyle is reduced due to poor vision. Generally the decision to refer should not be based on visual acuity, and the referral letter should reflect this. Patients who are not referred should not just be monitored until referral. There are several simple strategies for improving their vision which should be discussed with the patient, such as broad-brimmed hats or caps, typoscopes, anti-reflection coats and UV-blocking tints. There are also several strategies which may delay the progress of their cataract, which include reducing UV exposure and cigarette smoking and taking anti-oxidant vitamin supplements. These could also be discussed with the patient.

The use of accurate visual acuity measurements in clinical anti-cataract formulation trials.

A standardized visual acuity technique is presented for use in anti-cataract drug trials. Ferris Logmar charts were used in repeatability studies of vision, visual acuity and pinhole visual acuity measurements for twenty normal subjects (mean (+/- SD) age 64 +/- 6.3 years). Visual acuity measurements were shown to be the most repeatable and thought to be the most suitable for monitoring cataract progression. Repeated visual acuity measurements were made on 29 cataractous eyes of 15 subjects (mean (+/- SD) age 67.8 +/- 7.2 years). A Logmar score change of 0.1 (one line) was shown to be a statistically significant change. This value can be used in statistical analyses of drug efficacy. The normal data gives a mean Logmar visual acuity of 1.15 (Snellen equivalent 6/5). This indicates the inadequacy of using 6/6 as a norm value for visual acuity, even for older patients. As the possibility of reversal of cataract theoretically exists in the early stages of cortical and capsular cataracts, patients with small amounts of these types of cataract are ideal patients for anti-cataract formulation trials. The normal visual acuity results indicate that the inclusion criteria for clinical trials can include patients with cataracts with visual acuity as good as 6/6.

Simple clinical techniques to evaluate visual function in patients with early cataract.

Among the 80 subjects who were recruited with normal retinal and neural function, 54 had cataract and a visual acuity (VA) better than 6/24. The 26 age-matched subjects had clear media. Contrast sensitivity (CS) at low and intermediate spatial frequencies was measured using the Pelli-Robson letter chart. Two measures of glare disability (GD) were obtained using the Mentor Brightness Acuity Tester (BAT) in conjunction with a logMAR VA chart and the Pelli-Robson chart. Although CS is predominantly affected at high spatial frequencies in early cataract, we found that some subjects had reduced scores on the Pelli-Robson chart. This CS loss could not be predicted from VA measurements and was particularly found in subjects with posterior subcapsular cataract. High GD scores were found in a number of subjects with relatively good VA and could not be predicted from results of VA or CS. We suggest that CS and GD measurements using the Pelli-Robson chart and the BAT provide valuable information regarding the management of patients with early cataract.