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A hand optometer for measuring dark focus.

To measure the accommodative state of the eye in a stimulus free condition, the so called dark focus, a simple optometer was constructed based on the principle of the polarized vernier optometer originally proposed by Moses (1971). Data obtained with this hand optometer were compared with those of two other subjective techniques, the polarized vernier optometer and the laser optometer, we were found to be similar. The advantage of this hand optometer is that it is a convenient device that allows one to measure the dark focus within minutes, under normal room lighting.

Accommodation, Ocular↗

The frequency characteristics of accommodative microfluctuations for central and peripheral zones of the human crystalline lens.

Temporal variations in the nominally steady-state accommodation response can be characterized approximately by two principal regions of dominant activity: a low frequency region (LFR less than 0.6 Hz) and a high frequency region (HFR greater than 1.0 Hz). The observed changes of activity in the LFR induced by varying stimulus conditions has led to the proposal that this region may be utilized as an error detector in the accommodation feed-back loop. The role of fluctuations in the HFR is, however, equivocal particularly as several reports have shown their magnitude to be positively correlated with pupil size. The implication is that HFRs are a consequence of the mechanical and elastic properties of peripheral rather than central zones of the crystalline lens and hence do not contribute to the accommodation control process. The aim of the study was to compare the incidence and magnitude of microfluctuations in LFRs and HFRs for central and peripheral lens zones when viewing a near target. Accommodation was measured continuously with a modified Canon Autoref R1 infra-red optometer on five young emmetropic subjects. We show that although the total power of the microfluctuations is reduced in the periphery, the form of the power spectra is similar for central and peripheral zones. Thus rather than being spurious effects caused by the periphery of the lens HFRs are present for both central and peripheral lens zones.

Accommodation, Ocular↗

The influence of chromatic aberration on the static accommodative response.

Previous measurements of static accommodation have consistently shown steady state errors over most of the range; the response lags below the stimulus and, at low levels, the response leads the stimulus. A series of experiments is presented in which the longitudinal and, for the first time, transverse chromatic aberrations of the eye were varied and the resultant stimulus-response functions of accommodation were measured. The results show that the steady state error of accommodation is not influenced by manipulations of the magnitude or the direction of either longitudinal or transverse chromatic aberration. This indicates that a particular wavelength is not preferentially focussed on the retina as a function of stimulus level and supports the negative feedback theory of accommodation.

Accommodation, Ocular↗

Chromatic aberration and ocular focus: Fincham revisited.

Longitudinal chromatic aberration of the eye (LCA) produces "color fringes" at edges that specify focus. Fincham [(1951) British Journal of Ophthalmology, 35, 381-393] concluded that these chromatic effects were important for accommodation, but most investigators disagree. We monitored accommodation in 25 subjects while they viewed a sinusoidally moving target (1.5-2.5 D at 0.2 Hz) in a Badal optometer. The target was monochromatic (590 nm with 10 nm bandwidth), or white (3000 K) with LCA normal, neutralized or reversed. Sensitivity to the effects of LCA is profound and widespread. Gain decreases substantially and phase-lag increases when LCA is eliminated, and reversing the aberration severely disrupts accommodation. The ordered arrangement of spectral foci produced by LCA seems to be a fundamental aspect of the stimulus for "reflex" accommodation.

Accommodation, Ocular↗

Measurement of monochromatic ocular aberrations of human eyes as a function of accommodation by the Howland aberroscope technique.

Further development of the objective version of the Howland and Howland [(1976) Science, 193, 580-582; (1977) Journal of the Optical Society of America, 67, 1508-1518] aberroscope technique for measuring ocular aberrations is described. Compensation for refractive corrections and calibration is discussed. The technique was used to investigate the effect of accommodation upon the monochromatic aberrations of the right eyes of 15 subjects. Coma and coma-like aberrations were the dominant aberrations for most people at different accommodation levels, thus confirming previous findings. Variations in aberrations were considerable between subjects. About half the subjects showed the classical trend towards negative spherical aberration with accommodation. Changes in spherical aberration with accommodation in this study were less than found in previous studies where all monochromatic aberration was considered to be spherical aberration.

Accommodation, Ocular↗

Lens accommodation evoked by microstimulation of the superior colliculus in the cat.

Accommodative responses to microstimulation of the superior colliculus (SC) of cats were investigated by measuring dioptric changes of the eye with a high-speed infrared optometer. Lens accommodation was elicited by low-current stimuli (< or = 20 microA) of the rostral portion of the SC, which corresponds to the representation of the central visual field. The low-threshold area for evoking lens accommodation was distributed from the superficial to intermediate layers of the SC. The latency of accommodative responses was 198.3 +/- 34.6 msec (mean and SD). The duration of accommodation was highly correlated with the duration of stimulation. These findings suggest that the SC plays an important role in the control of lens accommodation.

Accommodation, Ocular↗

A new simultaneous 1020-site optical recording system for monitoring neural activity using voltage-sensitive dyes.

We have constructed a new 1020-site optical system for simultaneous recording of transmembrane electrical activity, using a 34 x 34-element photodiode array. This new apparatus permits analyses of the spatio-temporal pattern of neural activity, such as action potentials and postsynaptic potentials, in the central nervous system, at higher spatial and temporal resolutions.

Action Potentials↗

Strategic regulatory entry deterrence: an empirical test in the ophthalmic market.

This paper provides an empirical test of the theory of strategic regulatory entry deterrence--the theory that subgroups of firms within an industry will use the regulatory process to increase rivals' costs and thereby deter rivals' entry. The results suggest that the commercial practice restrictions present in the ophthalmic industry deterred chain optical firms' entry into the market. This result in combination with earlier findings that the restrictions increase optometrists' prices suggests that cost-raising strategies can be used to disadvantage rivals or drive them out of the market without the need to lower price.

Commerce↗

The dioptron II's validity and reliability as a function of its three accuracy indices.

Confidence factor, missed scans and relation junction were confirmed as indices of the Dioptron II's validity. Consequently, a classification of the instrument's measurements was recommended. This gave three classes of finding, first, second and third, and it was subsequently verified that instrument test - retest reliability also related to class of result. Repetition of measurements which were not first-class improved instrument validity but only to a limited degree. The link between confidence factor, and astigmatism and cylinder angle discovered with the Dioptron I was corroborated with this version.

Computers↗

Automated refraction in aphakia--II. Its repeatability and accuracy compared to conventional techniques.

The repeatability and accuracy of an i.r. electronic optometer (the Ophthalmetron) and of retinoscopy performed by experienced practitioners were studied in aphakia by testing a group of 17 patients three times with each method and by subjective techniques. The results show that the Ophthalmetron gives better repeatability than retinoscopy and that accuracy is marginally better for the sphere with the Ophthalmetron and for the cylinder power by retinoscopy when the mean of the three subjective results is taken as the true refractive value.

Adult↗

Australia is 200.

Explore the source record for details and available documents.

Australia↗

The Bausch and Lomb keratometer does not measure the tangential radius of curvature.

The purpose of this research was to determine if the conventional keratometer measures tangential or sagittal radius. A Bausch and Lomb keratometer was modified to enable an assessment of vertex radius and p-value to be made on convex conicoidal buttons of known surface form. Calculation of these two parameters was achieved assuming that the keratometer was measuring tangential radius and then repeated assuming a sagittal measurement. The resulting values could then be compared with those obtained by Form Talysurf analysis and by the use of an autokeratometer designed to measure sagittal radius. There was good agreement between the three instruments when the modified Bausch and Lomb keratometer was assumed to measure sagittal radius. We conclude that the Bausch and Lomb keratometer makes a radius measurement closer to the sagittal than the tangential radius of a conicoid of revolution.

Anthropometry↗

Patient outcomes with co-managed post-operative care after cataract surgery.

This study examined the practice of co-managed post-operative care and the visual acuity outcomes and complications associated with co-managed services. Data on service utilization and medical outcomes were collected for 2822 cataract surgery procedures performed in 5 ambulatory eye centers between January and July 1988. Average age of patients was 72.8 (SD = 10.4) and 63% were female. Eighty-seven percent of eyes were co-managed. Average number of post-operative visits within 90 days was 4.7 and 6.2 for co-managed cases with and without complications, respectively. Successful visual acuity outcomes (< 20/40) were experienced by 86% of all co-managed patients. There was evidence that patients with pre-existing ocular conditions (e.g. glaucoma, macular degeneration) and serious post-surgical complications were not referred for co-management. For co-managed patients without pre-existing medical or ocular conditions, 92% had successful vision outcomes, while 77-90% with these conditions had successful outcomes. Ninety-three percent of co-managed cases had no post-operative complications, and the rate of specific types of complications ranged from 0.04 to 2.0%. Using physician evaluations as the standard, sensitivity of optometrist detection of complications was 59% and specificity was 99.6%. Optometrists located in separate offices demonstrated 95.8% accuracy in assessing patients for post-operative complications.

Aged↗

Visual training: current status in ophthalmology.

PURPOSE: To inform ophthalmologists of the current status of visual training. DESIGN: Personal perspective. METHOD: A perspective and analysis of current practices that include a review of the literature and personal experiences of the author. RESULTS: Visual training of some sort has been used for centuries. In the first half of the twentieth century, in cooperation with ophthalmologists, orthoptists introduced a wide variety of training techniques that were designed primarily to improve binocular function. In the second half of the twentieth century, visual training activities were taken up by optometrists and paramedical personnel to treat conditions that ranged from uncomfortable vision to poor reading or academic performance. Other visual training has been aimed at the elimination of a wide variety of systemic symptoms and for the specific improvement of sight and even for the improvement of athletic performance. At present, ophthalmologists and orthoptists use visual training to a very limited degree. Most visual training is now done by optometrists and others who say it works. Based on an assessment of claims and a study of published data, the consensus of ophthalmologists regarding visual training is that, except for near point of convergence exercises, visual training lacks documented evidence of effectiveness. CONCLUSION: Although visual training has been used for several centuries, it plays a minor and actually decreasing role in eye therapy used by the ophthalmologist. At the beginning of the twenty-first century, most visual training is carried out by non-ophthalmologists and is neither practiced nor endorsed in its broadest sense by ophthalmology.

Amblyopia↗