Anaerobic dechlorination and redox activities after full-scale Electrical Resistance Heating (ERH) of a TCE-contaminated aquifer

The effects of Electrical Resistance Heating (ERH) on dechlorination of TCE and redox conditions were investigated in this study. Aquifer and groundwater samples were collected prior to and after ERH treatment, where sediments were heated to approximately 100 degrees C. Sediment samples were collected from three locations and examined in microcosms for 250 to 400 days of incubation. Redox activities, in terms of consumed electron acceptors, were low in unamended microcosms with field-heated sediments, although they increased upon lactate-amendment. TCE was not dechlorinated or stalled at cDCE with field-heated sediments, which was similar or lower compared to the degree of dechlorination in unheated microcosms. However, in microcosms which were bioaugmented with a mixed anaerobic dechlorinating culture (KB-1) and lactate, dechlorination past cDCE to ethene was observed in field-heated sediments. Dechlorination and redox activities in microcosms with field-heated sediments were furthermore compared with controlled laboratory-heated microcosms, which were heated to 100 degrees C for 10 days and then slowly cooled to 10 degrees C. In laboratory-heated microcosms, TCE was not dechlorinated and redox activities remained low in unamended and lactate-amended sediments, although organic carbon was released to the aqueous phase. In contrast, in field-heated sediments, high aqueous concentrations of organic carbon were not observed in unamended microcosms, and TCE was dechlorinated to cDCE upon lactate amendment. This suggests that dechlorinating microorganisms survived the ERH or that groundwater flow through field-heated sediments carried microorganisms into the treated area and transported dissolved organic carbon downstream.

The symptomatic Pulfrich phenomenon can be successfully managed with a coloured lens in front of the good eye--a long-term follow-up study

PURPOSE

Many visual symptoms originating from a spontaneous Pulfrich phenomenon can be alleviated by the provision of a tinted lens worn in front of the least affected eye. Here, we report on the long-term outcome of four patients who have been provided with a uniocular tinted spectacle or contact lens.

METHODS

The case notes of four cases were reviewed. The review period was at least 5 years in all four cases.

RESULTS

In all cases, visual symptoms and perceptual difficulties occurring from the spontaneous Pulfrich effect were completely eliminated over a period of many years. In one case, the relief has been sustained over a 20-year period.

CONCLUSIONS

A uniocular tinted lens, or contact lens, provides immediate and lasting relief from the visual difficulties caused by the visual delay underlying the spontaneous Pulfrich effect.

Redox processes and release of organic matter after thermal treatment of a TCE-contaminated aquifer

Redox conditions in heated and unheated microcosm experiments were studied to evaluate the effect of thermal remediation treatment on biogeochemical processes in subsurface environments. The results were compared to field-scale observations from thermal treatments of contaminated sites. Trichloroethene-contaminated aquifer material and groundwater from Ft. Lewis, WA were incubated for 200 days at ambient temperature (i.e., 10 degrees C) or heated to 100 degrees C for 10 days and cooled slowly over a period of 150 days to mimic a thermal treatment. Increases of up to 14 mM dissolved organic carbon were observed in the aqueous phase after heating. Redox conditions did generally not change during heating in the laboratory experiment, and only minor changes occurred as an effect of heat treatment in the field. The conditions were slightly manganese/iron-reducing in two sediments and possibly sulfate-reducing in the third sediment based on production of up to 0.20 mM dissolved iron and 0.15 mM dissolved manganese and consumption of 0.08 mM sulfate. The calculated energy gain of less than -20 kJ/mol H2 for iron and sulfate reduction as well as methane production indicated that these processes were thermodynamically favorable. Sulfate reduction and methane production occurred in the unheated microcosms upon lactate amendment. Little or no reduction of the redox level was identified in heated lactate-amended microcosms, possibly because of limited microbial activity. Because the redox conditions, pH, and alkalinity remained within normal aquifer levels upon heating, bioaugmentation may be feasible for stimulating anaerobic dechlorination in heated samples or in future field applications.

Accommodation as a function of age and the linearity of the response dynamics

The changes with age in the accommodation responses to dynamic stimuli can reveal useful information on the factors underlying presbyopia development. Analysis of the monocular accommodation responses of 19 normal observers (ages 18-49 years) to stimuli whose vergence varied sinusoidally with time at different temporal frequencies (peak-to-peak stimulus 1.33-2.38 D, at 0.05-1.00 Hz) showed that at all ages both the gain and phase of the response were essentially linear functions of the temporal frequency. Extrapolation of least-squares, regression line fits to the gain data for each subject gave the gain at zero frequency, G0, and the cut-off frequency, fc, at which the gain fell to zero. G0 reduced with age but fc remained essentially constant at about 1.7 Hz, up to at least the age of about 40. The magnitude of the response to step stimuli covering the same stimulus range was well correlated with the value of G0. The linear changes in phase lag with temporal frequency corresponded to simple time delays td. The time lag varied from close to zero for the youngest subjects to about 0.5 s for the subjects in their late forties. There was substantial variation between the responses of subjects of similar age: those subjects with high values of G0 also tended to have low values of td, both effects probably being due to the superior ability of some individuals to predict the sinusoidal changes in the accommodation stimulus. Comparison of theoretical step responses, derived by applying linear theory to the parameters obtained from the results for the sinusoidal stimuli, with the actual responses to unpredictable steps for the same subjects supports the view that prediction effects and other possible factors make linear theory inapplicable to this type of data. The results are discussed in the context of current ideas on the development of presbyopia: it is suggested that the constancy of fc with age is the result of the ciliary body maintaining its efficiency, whereas the fall in G0 and increase in td result from increases in lens rigidity.

Accommodation dynamics as a function of age

Experiments are described in which the dynamic accommodation response to a stimulus whose vergence was varying sinusoidally with time between 1.33 and 2.38 D was measured as a function of frequency for 19 subjects, with ages distributed between 18 and 49 years. Response to abrupt stimulus change between the same levels was also measured. The results showed that at any age, for the sinusoidal stimuli, gain fell with frequency and phase lag increased: at fixed frequency, gain fell with age and phase lag increased. Neither reaction nor response times for step stimuli changed with age. Analysis of the sinusoidal data suggests the possible existence of a cut-off frequency of about 2 Hz, which varies little with age and above which the system cannot respond. The phase data is compatible with the existence of a frequency-independent time delay, which increases with age from about 0.17 s at 20 years to 0.48 s at 40 years. The results are discussed in terms of current knowledge of the factors contributing to the development of presbyopia.

Age changes in the interactions between the accommodation and vergence systems

Experiments are described in which static and dynamic accommodation (Ar), accommodative convergence (AC), vergence (C) and convergence accommodation (CA) responses to small stimuli were measured dynamically in 13 subjects with ages in the range 16 to 48 years. Analysis showed that the amplitudes of both blur and disparity-driven accommodation declined significantly with age, whereas the two types of vergence response did not. As a result, the AC/Ar ratio rose significantly with age, whereas the CA/C ratio fell. No significant change with age was found in response latencies and durations.

Influence of chronic alcohol abuse and ensuing forced abstinence on static subjective accommodation function in humans

PURPOSE

Acute alcohol ingestion can change accommodation, but the long term effects of sustained alcohol consumption on accommodative function have not been studied in detail. This study was thus undertaken on individuals with a history of alcohol abuse.

METHODS

Thirty-seven male individuals aged 25-56 years (average 40 years) from an alcohol rehabilitation centre in Inverness, Scotland, were assessed on admission and after a week of forced abstinence. The results were compared to a paired age-matched set of control male subjects. The static amplitude of accommodation was measured by an RAF rule, and the pupil size measured with a pupil gauge.

RESULTS

On admission, the group mean measured amplitude of accommodation was 4.7 +/- 2.2 D (mean +/- SD). These values for the alcoholics were lower than age-matched controls (of 5.9 +/- 2.9 D). The slope of the age-dependent decline in RAF rule accommodation measures was significantly smaller for the alcoholics compared to controls (at 0.215 +/- 0.027 D/year versus 0.332 +/- 0.015 D/year, respectively; p < 0.001), with the younger alcoholics showing a greater impairment. Following abstinence, there was no measurable change in accommodation measured, indicating the lower amplitude in the alcoholics was not attributable to circulatory alcohol levels. The resting pupil diameter in the alcoholics was 4.37 +/- 0.63 mm compared to the controls of 3.97 +/- 0.75 mm, with a higher incidence of small pupils (< or = 3 mm) in the controls.

CONCLUSIONS

The results indicate that chronic alcohol use can adversely affect subjective static accommodation, especially in younger alcoholics, as well as cause slight mydriasis.

Dynamics of the accommodation response to abrupt changes in target vergence as a function of age

The dynamic accommodation responses to small, abrupt changes in an accommodation stimulus were studied in two experiments. In the first, responses of 19 subjects with ages distributed between 18 and 49 years were measured for step stimuli of +/- 1.05 D. In the second, responses to small step stimuli (+/- 0.75, +/- 1.75 D) were recorded for a group of six 'young' (mean age 22, range 16-26 years) and six 'old' (mean age 42, range 36-48 years) subjects. In both experiments, the low target vergences always lay within the accommodation range of all subjects. Whether the data were analysed in terms of simple reaction and response times, or in terms of the frequency response, no marked systematic changes with age were found in the dynamics of the response in either of the experiments. It is concluded that, for small stimuli within the amplitude of accommodation, the response dynamics over the adult age range studied remain remarkably constant, even though the amplitude progressively reduces with age as complete presbyopia is approached.

Changes in the static accommodation response with age

A transverse study of the monocular, steady-state accommodation response/stimulus curves for 49 normal subjects with ages between 17 and 49 years shows that the slope of the curve reduces only slowly with age up to about 40 years and then declines rapidly as complete presbyopia is approached. Such behaviour appears to result from the accommodation system changing its characteristics with age to make optimal use of the available objective amplitude of accommodation and the depth-of-focus of the eye.

Repeated measures of horizontal heterophoria

PURPOSE

To assess repeatability, horizontal heterophoria measurements were taken from 31 subjects on five occasions, each between 1 and 4 weeks apart.

METHOD

Distance heterophoria was measured using a Maddox Rod, and near heterophoria was measured using a Maddox Wing. In addition, near measurements were repeated with a +3.00 D lens in front of each eye to place the targets at optical infinity. In each case, the standard deviation of the five values was taken as a metric of the test variability.

RESULTS

On average, the variability of the Maddox Rod was half of the Maddox Wing, both with and without the lenses.

CONCLUSION

This consistency suggests that the difference reflects the test conditions rather than optical differences in the target position.

The measurement of pupil cycling time

PURPOSE

To assess the influence of pupil size on pupil cycling time (PCT), a measure which may be elongated in cases of neurological disease.

METHOD

Clinically, pupil "cycling" is produced by focusing a slit-lamp beam on the pupil margin. A rhythmic contraction and dilation of the pupil is produced, as changes in pupil size alternately prevent and allow the light beam to reach the retina. In this study, however, the light beam was controlled electronically so that cycling could be produced around different pupil sizes. Measurements of the variation of PCT with pupil size were taken from 22 young normal subjects.

RESULTS

PCT was seen to depend upon pupil size, increasing monotonically but non-linearly as size increased. The wave-form of pupil cycling is typically sawtooth, contraction being much faster than dilation. There was considerable variation amongst subjects in the range of pupil sizes where pupil cycling could be elicited.

CONCLUSIONS

The results point to the need for a standardised procedure for the measurement of cycling time, because differences in clinical conditions will themselves influence pupil size, as will other external variables such as ambient light level. The results also bring into question neurological explanations for increased PCT in those diseases where pupil size is affected, because normal subjects have PCTs well beyond the accepted limits of normality when their pupils are enlarged.

Reduced accommodative function in dyskinetic cerebral palsy: a novel management strategy

A 9-year-old boy with dyskinetic cerebral palsy secondary to neonatal encephalopathy is described. He presented with blurring of near vision which had begun to impact on his school work. Objective assessment of accommodation showed that very little was present, although convergence was almost normal. The near-vision symptoms were completely removed and reading dramatically improved with the provision of varifocal spectacles. Varifocal lenses provide an optimal correction for far, intermediate (i.e. for computer screens), and near distances (i.e. for reading). Managing this type of patient with varifocal spectacles has not been previously reported. It is clearly very important to prescribe an optimal spectacle correction to provide clear vision to optimize learning.

On the linearity of accommodation dynamics

Available experimental data on the gain and phase lags in the closed-loop accommodation responses to stimuli whose dioptric vergence changes sinusoidally with time are examined. It is shown that both phase lags and gain change almost linearly with the temporal frequency of the stimulus. This implies that the phase lags correspond to a frequency-independent time delay and that, if the system is linear, the impulse response should take a symmetrical (sin x/x)(2) form, with a corresponding standard form of step response. Comparison of this derived step response with the quasi-exponential results found experimentally underlines the limitations of attempting to generalize dynamic accommodation performance from responses obtained with predictable sinusoidally-changing stimuli and the application of a linear model. Consideration of the frequency response which would lead to an exponential step response supports the argument that, although the gain results obtained with sinusoidal stimuli are reasonably representative of those applying with other forms of stimulus, the predictable nature of sinusoidally-changing stimuli makes the derived phase lags inapplicable to non-predictable step or other stimuli. Other limitations in linear models of the response are discussed.

Accommodation responses and ageing

PURPOSE

To study the impact of age on accommodation dynamics.

METHODS

Monocular accommodation responses were measured continuously using a modified Canon Auto Ref R1 infrared optometer. The stimulus was a single letter oscillating sinusoidally between 2.38 and 1.33 D providing a stimulus amplitude of 0.52 D, about a mean level of 1.86 D. Response characteristics were used to quantify gain and phase. Step responses were also recorded between these stimulus vergence levels for calibration purposes and to measure reaction and response times. Nineteen visually normal subjects 18 to 49 years of age participated, and 11 frequencies were used in the range 0.05 to 1.0 Hz. A key feature of the experimental design was to use a stimulus vergence range that lay within the amplitude of accommodation of all the observers.

RESULTS

Accommodation gain reduced and phase lag increased with age, particularly at the higher frequencies used. No strongly significant change with age was found for reaction and response times or accommodation velocity, and results were similar for both far-to-near and near-to-far responses. Response amplitude for the step change in target vergence declined with age, and substantial differences were found between the measured and predicted (from reaction time) phase lags at 1.0 Hz as a function of age. Young observers showed a phase lag that was shorter than predicted, whereas older observers' measured phase lags were considerably larger than predicted.

CONCLUSIONS

Results show that for a target oscillating sinusoidally in a predictable manner at a modest amplitude, the main ageing effects occur in phase lag, which is appreciably longer than predicted from reaction times in the older observers. The effects of ageing on gain were not as marked. Although responses to small step changes do reduce with age, there is no evidence of increased response times with ageing. In general, accommodation function in the middle-aged eye is quite robust despite a dwindling amplitude of accommodation. These results provide evidence of accommodative vigor in youth and a slowing of accommodation with ageing.

Comprehensive audit of quality-of-care and quality-of-life for patients with diabetes

This comprehensive audit was conducted in a three-person general practice with an age-sex-disease register to evaluate care for patients with diabetes using metabolic indicators and validated measures of quality-of-life and patient satisfaction. Medical records were reviewed using criteria derived from guidelines published by Diabetes Australia and New South Wales Health. Self-administered questionnaires mailed to patients included the Diabetes Quality-of-Life measure (DQOL), the Well-Being Questionnaire (WBQ) and the Diabetes Treatment Satisfaction Questionnaire (DTSQ). Record audit for 71 patients with diabetes demonstrated poor control and monitoring. Frequent attenders were no more likely to have had a HgA1c performed than less frequent attenders (P = 0.72). While patient satisfaction with care was high, numerical values for quality-of-life were lower than published overseas norms, indicating a need to support better care in general practice and further research to determine Australian norms.

The Pulfrich effect in optometric practice

The Pulfrich effect can occur spontaneously, giving severe symptoms of changed visual perception in a variety of conditions in which an interocular latency difference has occurred. The symptoms principally involve misjudgements on the location of objects, especially when driving. Interocular latency differences can inadvertently be created in patients in practice and this study has investigated the Pulfrich effect in anisocoria, uniocular mydriasis, and with uniocular tint (X-chrom lens). In all cases a Pulfrich effect was consistently evident and compared to the size of the effect provoked by neutral density filters. The results show that with anisocoria, uniocular mydriasis and the X-chrom lens, the provoked Pulfrich effect is similar to that found reported previously in cases of trauma. These cases had severe visual symptoms so that care should be exercised in practice, where procedures likely to provoke the Pulfrich effect are contemplated. Specifically, patients who have received uniocular mydriasis in practice should be cautioned about the possible visual effects and advised not to drive until the effect of the mydriatic has finished and equal pupil sizes have been restored.

The fluctuations of accommodation and ageing

OBJECTIVE

The aim of this study was to investigate the influence of age on the fluctuations of accommodation.

METHOD

Fluctuations of accommodation were measured on six 'young' (16-25 years, mean age 22 years) observers and six 'older' (35-48 years, mean age 42 years) observers. Accommodation was continuously recorded using a SRI optometer whilst the observers steadily viewed a high contrast target at stimulus levels 0.25 D, 1.00 D and 2.00 D. Fluctuations were quantified using power spectrum analysis, and frequencies were grouped into bands: low (LFC 0.3-0.6 Hz and 0.3-0.9 Hz) and high (HFC 1.1-2.2 Hz).

RESULTS

Accommodation response levels for these stimuli for both groups of observers were quite similar. Fourier analysis was used to generate power spectra so that the fluctuations of accommodation for each observer group could be compared. In general power increased for increasing response levels for both groups of observers, although less power was evident for the older observers in both LFC and HFC bands. Differences in power were not significant at these frequency bands for the two observer groups. When the whole power spectrum is compared these differences became significant with more power evident in the younger cohort.

CONCLUSION

Reductions in both amplitude and speed of accommodation with age are well known, and the decline in magnitude of the fluctuations found here is consistent with a general diminution in accommodation dynamics as the accommodation mechanism ages. For the older group, some of who were near absolute presbyopia, there may be little contribution to power from changes in lens shape and it is possible that small changes in lens position in the eye contribute to the power spectrum.

Comparison of age-related changes in short-wavelength-sensitive cone thresholds between normals and patients with primary open-angle glaucoma

PURPOSE

To establish the effect of aging upon short-wavelength-sensitive cone (S-cone) sensitivity for both normals and patients with primary open-angle glaucoma (POAG).

METHODS

S-cone thresholds were established for the detection of blue test spots on a bright yellow adapting background. Detection thresholds for combined medium- and long-wavelength-sensitive cones (M/L-cones) were also established for a yellow test spot upon a yellow background. A group of 177 normal subjects (age range 20 to 80 years) and 46 glaucoma subjects were examined.

RESULTS

The rate of decline of S-cone sensitivity with increasing age was found to be similar in patients with POAG and age-matched normals (approximately 0.2 log units/decade), although S-cone sensitivity in the POAG population was significantly lower (p < 0.05) than that in age-matched normals by approximately 0.3 log units.

CONCLUSIONS

The results of the present investigation show an age-related decline in S-cone sensitivity for both normals and patients with POAG. The decline in S-cone sensitivity within the POAG population is similar to that occurring in normal subjects when the two populations are matched for age.

Relationship between visual acuity and observation distance

The visual acuities of 17 young emmetropes and corrected ametropes were measured over the range of 7.5-0.19 m using a Bailey-Lovie chart. Accommodation stimulus-response measures were also taken over this range using retinoscopy to establish whether variations in visual acuity with observation distance could be attributed to accommodation behaviour. Tonic accommodation was recorded using the Canon R1 autorefractor and was compared with visual acuity and stimulus-response results. In general, visual acuity was found to be dependent on stimulus distance, being significantly reduced for most observers for the closest targets. There were three categories of observer performance for visual acuity as a function of observation distance; one group showing no change in visual acuity with distance, a second showing a flat function for distances 7.55-0.5 m, and then a decrease in visual acuity for shorter distances; and a third category that showed a maximum visual acuity in the 1.2-1.6 m region. This behaviour was unrelated to individual stimulus-response characteristics and there was no significant relationship between tonic accommodation and the distance where acuity was best for the third category observers.

Impaired perception of moving objects after minor injuries to the eye and midface: the Pulfrich phenomenon

Delayed conduction along one optic nerve can result in an incorrect appreciation of moving objects. The temporal mismatch between the two different pathways results in altered perception of the vector of a moving target and is known as 'the Pulfrich phenomenon'. This is a well-recognised handicap in patients with multiple sclerosis, but has not previously been reported as a consequence of injury. All 187 patients who presented during 1991 with reduced visual acuity as a result of midfacial injuries were examined with a pendulum. Six had the defect and five of these had symptoms. In each case the patients were disturbed by car travel, because they perceived oncoming traffic moving in a hyperbolic curve towards them. These patients have been examined in detail and given a tinted lens for the normal eye to eliminate the illusion by delaying the input from the normal side to equal that on the damaged side. We recommend that this phenomenon is sought in all patients with mid-facial injuries or with later evidence of mild traumatic optic neuropathy, particularly if they are disturbed by car travel.

The simultaneous interocular brightness sense test. A test of optic nerve function

OBJECTIVE

To describe and establish control data from controls for a simultaneous interocular brightness sense test in which the apparent brightness of two independently viewed light patches was compared.

DESIGN

Dichoptic viewing was achieved by dissociation of right and left eyes using a septum and cross-polarization. Brightness matches were obtained by using adjustments to the illumination of the left retina while the illumination of the right retina was kept constant. OBSERVERS: Ninety-one control observers (age range, 20 to 91 years) participated in the study to provide normal brightness-matching data.

RESULTS

Effects from ocular dominance, age, and long- and short-term adaptation were negligible, but the test was sensitive to anisocoria. Just noticeable differences in dichoptic brightness matching were proportional to retinal illuminance; this finding was consistent with the Weber-Fechner law.

CONCLUSION

The test is quick and simple to complete and appears to offer considerable scope for the assessment of visual function when differences in the functional integrity of the optic nerves of the right and left eyes are suspected.

Simultaneous interocular brightness sense testing in ocular hypertension and glaucoma

OBJECTIVE

To investigate the performance of the simultaneous interocular brightness sense test in patients with ocular hypertension and primary open angle glaucoma (POAG).

DESIGN

Brightness matches were obtained for an age-matched control sample and for patients with ocular hypertension and POAG. In addition, for the patients with POAG, visual field defects were quantified and a risk factor count was established for those with ocular hypertension.

PATIENTS

Nineteen patients with ocular hypertension, 20 patients with POAG, and 61 age-matched controls participated in the study.

RESULTS

Seven patients with ocular hypertension exhibited brightness perception asymmetry outside normal limits for age-matched controls. Of these, six were at high risk of having glaucoma develop and only one of the remaining 12 was found to be at similar risk. All 20 patients with established POAG had results outside the normal limits for a test sensitivity of 100%. Three control observers had abnormal results, giving a test specificity of 95%.

CONCLUSION

The simultaneous interocular brightness sense test is quick and simple to perform and is suitable for a wide age range of patients. It warrants further assessment as a means of screening for ocular hypertension and glaucoma.

Colour vision screening in glaucoma: the Tritan Album and other simple tests

Results from simple colour vision tests used for the detection of the Type III colour vision deficiency in glaucoma and ocular hypertension are presented. We assessed 49 patients with primary open angle glaucoma, 16 ocular hypertensives, 54 age matched normals and 50 young normal observers using six established tests and the recently introduced Tritan Album. This test was introduced specifically for acquired colour vision deficiencies. Results show in general that individual tests have low sensitivity and poor screening efficiency. The best screening efficiency was achieved by the City University Colour Vision Test and the AO HRR plate test, no acquired tritan defects were identified by the Farnsworth F2 plate, and the Tritan Album had very low sensitivity (the lowest excluding the F2 plate). Best results were obtained from a combination of City University and HRR test scores and this combination could provide useful additional data on colour vision in a glaucoma screening programme.

Location of nonlinear processes within the pupillary pathway

The pupil oscillates in synchrony with a slow beat produced by adding two lights flickering at slightly different frequencies. This behavior shows that nonlinear processes are present within the pathway. To localize these processes, a light of one frequency was presented to one eye, while a light of a different frequency was presented to the other. No pupil oscillations were seen in response to the beat in these dichoptic conditions, but when both lights were superimposed and presented to the same eye a powerful pupillary response was produced. We conclude that the nonlinearity giving rise to the pupil's beat response occurs before the pathways from the two eyes join and hence is neural rather than muscular in origin. Furthermore, the lack of a pupil response in the dichoptic conditions suggests that the signals from the two eyes may combine linearly.

The Pulfrich phenomenon and its alleviation with a neutral density filter

A case is described in which a presumed vascular accident resulted in long-standing visual difficulties in both reading and the analysis of vectors of moving objects. Clinical examination revealed minimal right optic atrophy with a relative superior altitudinal visual field defect associated with a positive Pulfrich effect. A partial head turn to the right in association with paresis of saccades and pursuit eye movements to the right was also evident. Spectacles for distance which incorporated a neutral density filter before the left eye were prescribed. These practically eliminated the Pulfrich effect and alleviated the problems of vector analysis. A near correction was provided which incorporated prisms with bases to the right. This eliminated the reading difficulties. The visual problems experienced by patients suffering from a positive Pulfrich effect are described and discussed.

Binocular accommodation reaction and response times for normal observers

Accommodation was recorded from right and left eyes of visually normal observers in both binocular and monocular viewing. Reaction and response times were similar in monocular and binocular viewing and are not influenced by eye dominance. Far-to-near responses were significantly quicker than near-to-far responses. The origin of this difference may be a feature of the elastic properties of the accommodation mechanism. Limited data are presented that indicate that the slowing of accommodation speed with age affects the near-to-far response disproportionally. Errors in the initial direction of response were fewer in binocular viewing in comparison with monocular viewing.

Twin channel infrared optometer for recording binocular accommodation

A twin channel infrared (IR) optometer for recording accommodation from each eye is described. Some modifications to a conventional single channel optometer design are necessary to facilitate binocular recording. The optometer incorporates an on-line microcomputer for data acquisition and processing. Processing includes power spectrum and correlation analysis, and a facility for performing cursor controlled measurement of time delays. Accommodation responses recorded are shown to be independent of horizontal eye movements, and little affected by the drug used for mydriasis.

Fluctuations in accommodation: a review

When a young observer attempts to accommodate steadily on a fixed stimulus, the nominally steady-state response shows small instabilities or fluctuations (sometimes termed microfluctuations or oscillations). These fluctuations typically have an amplitude of a few tenths of a dioptre and a frequency spectrum extending up to a few Hertz. The properties of these fluctuations are described for various viewing conditions: pupil diameter, target vergence, target form, target contrast, and target luminance all influence the frequency spectra of the oscillations, as may anomalies of vision such as amblyopia. The possible roles that the fluctuations might play in the function of the accommodative system are discussed. It is suggested that the higher frequency components around 2 Hz may arise from the mechanical and elastic characteristics of the lens, zonule and ciliary body. Components at lower frequencies (less than 0.5 Hz) may be of more significance in the function of the accommodative control system.

Central visual fields for short wavelength sensitive pathways in glaucoma and ocular hypertension

While conventional clinical visual acuity and kinetic visual fields may be essentially normal in ocular hypertension and early stages of glaucoma, other foveal aspects of vision (eg color, spatial and temporal contrast sensitivity) may be quite abnormal. Specifically, a selective vulnerability of the short wavelength sensitive (SWS) visual pathways in these conditions has previously been noted. Here we studied the central visual fields of 33 primary open angle glaucoma (POAG) patients, 32 ocular hypertensives (OHT), and 24 age-matched normal controls using blue and yellow test flashes on bright yellow backgrounds. SWS cone and MWS and/or LWS cone pathway sensitivities were measured at the fovea and at 2.5 degrees, 5 degrees, 10 degrees and 15 degrees eccentricities, in either the inferior temporal (for OHT) or horizontal nasal retina (for POAG). As expected, all groups had normal sensitivity to yellow flashes--detected by LWS and/or MWS cones--in these meridians. By comparison, for the blue flashes--detected by the SWS cones--the POAG and OHT groups had sensitivity deficits, uniformly across the central visual field, of about 6X and 1.8X, respectively, compared to normals. While six of 31 (19%) OHT subjects had localized glaucomatous field defects (greater than 0.4 log units) in the non-foveal inferior temporal retina, none of the 12 OHT subjects who were also tested in the horizontal nasal retina showed loss in this meridian. Finally, while no POAG subjects had localized sensitivity loss for yellow flashes in the horizontal nasal retina, four did show local field defects with blue test flashes.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical measures of central vision function in glaucoma and ocular hypertension

A generalized loss of visual sensitivity, even for foveal targets, has been reported as an early sign of glaucoma. In the present study of central vision, we used relatively simple and rapid clinical tests of color thresholds, color discrimination, and spatial contrast sensitivity to compare the vision of three age-matched groups of patients who had primary open angle glaucoma (n = 33) or ocular hypertension (n = 32) as well as normal subjects (n = 24). The largest sensitivity losses for both glaucoma and ocular hypertensive groups were disclosed by a color threshold test with blue lights designed to isolate the blue-sensitive pathways of the visual system. The loss of sensitivity for both the glaucoma group and the ocular hypertensive group is consistent with recent reports (from postmortem studies of human eyes) of extensive axon death even in the absence of glaucomatous field defects.

Stereoscopic threshold in children and adults

The threshold of stereoacuity is reported as measured on 369 normal children aged 3 to 7 years, and on 51 normal adults. Four standard clinical stereotests were used and two different testing procedures adopted. The results show that both threshold and variability decrease with age, and performance becomes adult-like at different ages for different tests. Interest correlations are poor, and in cases where the correlation is significant, no identifiable pattern emerges between testing procedures, age, and stereotests. The procedures themselves gave no significant difference in stereoacuity values between all four tests.