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PubMed1988

Effect of pupil size on dark focus accommodation.

A potential concern in some studies of dark focus accommodation is the role of pupil size (and related spherical aberration) in laser optometer measurements. Dark focus measurements were obtained for 25 young adult subjects while they viewed the laser speckle pattern through artificial pupils of 3, 4, 5, 6, 7 and 8 mm diameter. Analysis showed no significant effect of pupil size on dark focus. It would appear that pupil size variations should not be a source of concern in laser optometer dark focus assessment.

Accommodation, Ocular↗
PubMed1992

Retinal information capacity and the function of the pupil.

When the pupil is opened to increase sensitivity there is a loss of image sharpness due to aberrations. This trade-off between sensitivity and sharpness is analysed theoretically by calculating the information capacity of the retinal image. The analysis uses optical measurements of image sharpness made at different pupil diameters. At each luminance there is a pupil diameter that maximizes information capacity. This optimum is close to the diameter adopted under normal viewing conditions. The optimum is broad, consequently the system tolerates inaccurate adjustment. The benefits of correctly adjusting the pupil are evaluated. At low light levels the advantage is 68%, at intermediate levels it falls to around 20% but under daylight conditions it increases to 52%. These advantages suggest that the primary function of the pupillary light reflex is to maximize acuity over a wide range of luminances.

Contrast Sensitivity↗
PubMed1998

Examination of the two-dimensional pupil function in coherent scanning microscopes using spherical particles.

The determination of the modulus of the pupil function in reflection acoustic and optical microscopy with the help of spherical particles is demonstrated. The theoretical examination shows that this method can give good results if the pupil function drops smoothly towards the edge. For a pupil with a sharp edge this technique can give the accurate pupil function only by imaging large spheres. The dependence of the accuracy of the method on the size of the spherical particle is analyzed. Numerical and experimental results obtained for the confocal scanning optical microscope and the scanning acoustic microscope are examined.

Acoustics↗
PubMed1983

Evidence for a neuropathic aetiology in the small pupil of diabetes mellitus.

Infrared television pupillometry was performed on 34 insulin-treated diabetic patients and 55 healthy subjects. Sixteen of the diabetic patients had pupils that failed to dilate normally in darkness. The occurrence of a small pupil was associated with cardiac vagal dysfunction and somatic sensory loss. The small pupil was found to be supersensitive to the mydriatic effect of topical 2% phenylephrine but normally sensitive to 0.5% hydroxyamphetamine eyedrops. It is concluded that the failure of the pupil to dilate in darkness in some diabetic patients is due to neuropathy of the sympathetic innervation.

Adolescent↗
PubMed1995

Pupil size and reactivity following hydroxypropyl methylcellulose and sodium hyaluronate.

AIMS: A prospective randomised clinical trial was set up to compare the effect of hydroxypropyl methylcellulose (Ocucoat) and sodium hyaluronate (Healonid) on pupil size and reactivity following their use in cataract surgery. METHODS: Pupil measurements were recorded before and 6 weeks after surgery. RESULTS: There was no significant difference between the two groups with respect to pupil size (p = 0.69, Mann-Whitney U test) nor with respect to reactivity (p = 0.99, Fischer's exact test). Ninety six per cent of the surgery was performed using phacoemulsification. CONCLUSION: This trial suggests that both viscoelastic materials have similar effects on the pupil after their use in cataract surgery.

Adult↗
PubMed1981

Pupil size and the pattern evoked visual response.

The effect of artificially varying the pupil size upon the pattern evoked visual response was examined in six healthy subjects and six patients with multiple sclerosis who had abnormal visual evoked responses. Slight depression of amplitude was seen whether the pupil was small or large, but the most obvious effect was a reduction of latency with a large pupil and an increase of latency with a small pupil. It is suggested these phenomena relate to the amount of light entering the eye and not any change of acuity.

Adolescent↗
PubMed2004

Variability of wavefront aberration measurements in small pupil sizes using a clinical Shack-Hartmann aberrometer.

BACKGROUND: Recently, instruments for the measurement of wavefront aberration in the living human eye have been widely available for clinical applications. Despite the extensive background experience on wavefront sensing for research purposes, the information derived from such instrumentation in a clinical setting should not be considered a priori precise. We report on the variability of such an instrument at two different pupil sizes. METHODS: A clinical aberrometer (COAS Wavefront Scienses, Ltd) based on the Shack-Hartmann principle was employed in this study. Fifty consecutive measurements were performed on each right eye of four subjects. We compared the variance of individual Zernike expansion coefficients as determined by the aberrometer with the variance of coefficients calculated using a mathematical method for scaling the expansion coefficients to reconstruct wavefront aberration for a reduced-size pupil. RESULTS: Wavefront aberration exhibits a marked variance of the order of 0.45 microns near the edge of the pupil whereas the central part appears to be measured more consistently. Dispersion of Zernike expansion coefficients was lower when calculated by the scaling method for a pupil diameter of 3 mm as compared to the one introduced when only the central 3 mm of the Shack - Hartmann image was evaluated. Signal-to-noise ratio was lower for higher order aberrations than for low order coefficients corresponding to the sphero-cylindrical error. For each subject a number of Zernike expansion coefficients was below noise level and should not be considered trustworthy. CONCLUSION: Wavefront aberration data used in clinical care should not be extracted from a single measurement, which represents only a static snapshot of a dynamically changing aberration pattern. This observation must be taken into account in order to prevent ambiguous conclusions in clinical practice and especially in refractive surgery.

Adult↗
PubMed2002

The eyes of suckermouth armoured catfish (Loricariidae, subfamily Hypostomus): pupil response, lenticular longitudinal spherical aberration and retinal topography.

The dilated, round pupils of a species of suckermouth armoured catfish (Liposarcus pardalis) constrict slowly on illumination (over 35-40 min) to form crescent-shaped apertures. Ray tracing of He-Ne laser beams shows that the lenses of a related species (Pterygoplichthys etentaculus), which also has a crescent-shaped pupil, are well corrected for longitudinal spherical aberration, suggesting that the primary purpose of the irregular pupil in armoured catfish is not to correct such aberration. It is suggested that the iris operculum may serve to camouflage the pupil of these substrate-dwelling species. An examination of the catfish retina shows the photoreceptors to be exclusively single cones interspersed with elongate rods and demonstrates the presence of multiple optic nerve head papillae. Two areas of high ganglion cell density, each side of a vertically oriented falciform process, provide increased spatial resolving power along the axes examining the substrate in front of and behind the animal.

Animals↗
PubMed1993

Color matching at high illuminances: photopigment optical density and pupil entry.

Changes in the effective optical density of the cones are sufficient to explain changes in color matches with retinal illuminance and pupil entry. We performed three experiments. In the first experiment, six observers made color matches under both bleached and unbleached conditions to a series of six standard wavelengths. The effects of bleaching could be modeled by a decrease in optical density of the L and M cone photopigments. Slight spectral shifts in the peak wavelengths of the photopigments were required for different observers. In the second experiment we varied retinal illuminance of the color-matching field from 2.4 to 5.4 log Td for a series of long-wavelength primaries. The shape of the color match versus the intensity function was unchanged by the wavelength composition of the matching field. In the third experiment we measured the change in color match with retinal illuminance for different pupil entry positions. At low luminances there was a marked dependence of the color match on pupil entry positions. At high illuminance there was only a small dependence. The half-bleach illuminance values varied as expected from the Stiles-Crawford I effect. We conclude that for wavelengths > 540 nm, changes in color matches with bleaching and pupil entry can be explained by changes in the effective optical density of the cones.

Adult↗
PubMed1995

Statistical distribution of foveal transverse chromatic aberration, pupil centration, and angle psi in a population of young adult eyes.

Subjective transverse chromatic aberration (sTCA) manifest at the fovea was determined for a population of 85 young adults (19-38 years old) by means of a two-dimensional, two-color, vernier alignment technique. The statistical distribution of sTCA was well fitted by a bivariate Gaussian function with mean values that were not significantly different from zero in either the horizontal or the vertical direction. We conclude from this result that a hypothetical, average eye representing the population mean of human eyes with medium-sized pupils is free of foveal sTCA. However, the absolute magnitude of sTCA for any given individual was often significantly greater than zero and ranged from 0.05 to 2.67 arcmin for the red and the blue lights of a computer monitor (mean wavelengths, 605 and 497 nm, respectively). The statistical distribution of the absolute magnitude of sTCA was well described by a Rayleigh probability distribution with a mean of 0.8 arcmin. A simple device useful for population screening in a clinical setting was also tested and gave concordant results. Assuming that sTCA at the fovea is due to decentering of the pupil with respect to the visual axis, we infer from these results that the pupil is, on average, well centered in human eyes. The average magnitude of pupil decentration in individual eyes is less than 0.5 mm, which corresponds to psi = 3 deg for the angle between the achromatic and the visual axes of the eye.

Accommodation, Ocular↗
PubMed2002

Scaling Zernike expansion coefficients to different pupil sizes.

Recent developments in technologies to correct aberrations in the eye have fostered extensive research in wave-front sensing of the eye, resulting in many reports of Zernike expansions of wave-front errors of the eye. For different reports of Zernike expansions, to be compared, the same pupil diameter is required. Since no standard pupil size has been established for reporting these results, a technique for converting Zernike expansion coefficients from one pupil size to another is needed. This investigation derives relationships between the Zernike expansion coefficients for two different pupil sizes.

Humans↗
PubMed2005

[Bilateral tonic pupil as the only remaining ophthalmic sign of Lyme disease: case report].

Lyme disease is a multisystemic disorder caused by Borrelia burgdorferi spirochete, transmitted by ticks. Mainly described in the northern hemisphere and rarely in Brazil. The purpose of this report is to describe a patient with Lyme disease who developed bilateral tonic pupil as the only remaining sign. A 13-year-old female with Lyme disease, presented with bilateral peripheral facial and oculomotor paralysis. After recovery from neurological abnormalities the patient sustained anisocoria, reduced fotomotor reflex, less than normal amplitude of accommodation, tonic pupil constriction for near objects and slow redialation in both eyes. Dilute 0.1% pilocarpine test was positive in both eyes, confirming the suspicion of bilateral tonic pupil. This is the first case report of bilateral tonic pupil caused by Lyme disease.

Adolescent↗
PubMed2001

Pupil size following dark adaptation in patients with retinitis pigmentosa.

According to the equivalent light hypothesis, molecular defects in the photoreceptor lead to a continuous activation of the photoreceptor cascade in a manner equivalent to real light. The consequences in diseases such as retinitis pigmentosa (RP) are as disruptive to the cells as real light. Two forms of the equivalent light hypothesis can be distinguished: strong - mutations in rhodopsin or other cascade proteins in some forms of RP continuously excite the visual phototransduction cascade; weak - disruption of outer segments in all patients with RP eliminates circulating dark current and blocks neurotransmitter release in a manner similar to real light. Both forms of the equivalent light hypothesis predict that pupils of patients with RP will be constricted like those of normal subjects in the light. The purpose of this study was to test the equivalent light hypothesis by determining whether steady-state pupil diameter following full dark adaptation is abnormally small in any of a sample of patients with RP. Thirty-five patients with RP and 15 normal subjects were tested. Direct steady-state pupillometric measures were obtained from one eye in a full-field dome after 45 min of dark adaptation by videotaping the pupil with an infrared camera. Mean pupil diameter in the dark was comparable (t = -0.15, P = 0.88) between patients with RP (6.85 +/- 0.58 mm) and normal subjects (6.82 +/- 0.76 mm). The results of the present study are clearly counter to the prediction of the second (weaker) form of the equivalent light hypothesis.

Adult↗
PubMedDate not supplied

Reduction of pupil size and halos with minus lenses after laser in situ keratomileusis.

PURPOSE: To evaluate the amount of miosis induced by over-minused lenses and to assess subjective reduction of halos following laser in situ keratomileusis (LASIK) with such lenses. METHODS: Part I: Infrared pupil diameter was assessed in 14 patients who had not had ocular surgery. The accommodative/miotic reflex was stimulated with concave trial lenses in -1.00-D increments up to -4.00 D while viewing the 20/40 acuity line. Part II. Subjective halos around a distant light were assessed in 14 patients following LASIK for myopia, with and without a -1.00-D lens over manifest refraction. RESULTS: Part I: 100%, 79%, and 64% of patients clearly saw the 20/40 line with a -1.00-D lens, -2.00-D lens, and -3.00/-4.00-D lens, respectively. Mean pupil diameter decreased by 0.2 mm with the -1.00-D lens (P = .02), 0.5 mm with the -2.00-D lens (P = .003), 0.9 mm with the -3.00-D lens (P = .008,), and 1.1 mm with the -4.00-D lens (P = .008). Part II: 11 of 14 patients (79%) noticed a decrease in the size of the halo (30% average reduction) when over-minused by -1.00 D. CONCLUSIONS: Pupil diameters and halos decreased with a -1.00-D overcorrection in patients following LASIK. Patients with pupil-dependent night halos after LASIK may benefit from mildly over-minused lenses.

Accommodation, Ocular↗
PubMedDate not supplied

Limitations of pupil tracking in refractive surgery: systematic error in determination of corneal locations.

PURPOSE: The goal of this investigation was to show the theoretical limitations of pupil tracking in refractive surgery. The parallax error associated with localizing corneal positions by tracking the subjacent entrance pupil center was quantified. METHODS: Optical ray-tracing in a schematic model eye was performed to determine the geometric parallax error. The calculations required several assumptions regarding ocular geometry, eye movements, and eye tracker position. Various parameter combinations were evaluated to assess the potential range of error to be expected in clinical practice. RESULTS: Tracking error can amount to 30% (or more for eye trackers mounted closer than 500 mm to the eye) of the detected lateral shift. Thus, if the eye tracker registers a lateral shift of the entrance pupil of 0.2 mm away from the tracking reference axis, the point of interest located on the cornea would essentially be 0.26 mm away from this reference axis. A laser pulse fired at that moment would be systematically displaced by 60 microm. Our results depended on geometric parameters of the eye and the tracking device. Based on conservative assumptions regarding these geometric parameters, partial compensation could be realized by adding a certain percentage to the modulus of each eye tracker reading. CONCLUSIONS: The fact that corneal displacement was generally underestimated by up to 30% of the measured entrance pupil shift demonstrates the severity of the parallax effect.

Cornea↗
PubMedDate not supplied

Theoretical effect of changes in entrance pupil magnification on wavefront-guided laser refractive corneal surgery.

PURPOSE: To explore theoretically the effect on the correction of higher order aberrations of changes in the magnification between the aperture stop (iris) and entrance pupil of the eye, following myopic excimer laser ablation. METHODS: Using a simple schematic eye model, paraxial calculations were made of the position and magnification of the entrance pupil of the eye as a function of the power of a myopic photorefractive keratectomy correction. RESULTS: Corneal flattening following myopic corneal ablation results in a reduction in the magnification between the aperture stop (iris) and entrance pupil. This implies that an ablation designed to correct higher order errors on the basis of the preoperative wavefront aberration across the entrance pupil will result in an incomplete correction. Taking into account the fact that the total ocular aberration depends on the combined effects of all optical components of the eye, which are distributed in depth, rather than being associated simply with the anterior surface of the cornea, the exact effects depend on the methods used to measure the aberration and the distribution of the total aberration between the different components of the eye. The errors in correction increase with the magnitude of the myopic correction. CONCLUSIONS: To minimize the postoperative higher order aberrations in higher amounts of myopia, it may be desirable to remeasure them after a first ablation to correct the second-order refractive errors and then to carry out a second ablation to correct the higher order aberrations.

Cornea↗
PubMedDate not supplied

The effect of pupil dilation on scanning laser polarimetry with variable corneal compensation.

BACKGROUND AND OBJECTIVE: The feasibility and reproducibility of scanning laser polarimetry performed through dilated pupils rather than through non-dilated pupils was tested. PATIENTS AND METHODS: One eye each of 36 subjects (12 normal, 12 suspected glaucoma, and 12 glaucoma) was scanned using a single GDx unit with variable corneal compensator (GDx-VCC; Laser Diagnostic Technologies, Inc., San Diego, CA). Two scans prior to and two scans after dilation were performed on each study eye, resetting the cornea compensation prior to each scan. The dilated eye was viewed off-center, such that the whitish focusing patch was projected on the 9-o'clock peripheral iris. After adequate anteroposterior focus, the pupil was centered and a scan was acquired. Each of 5 GDx parameters was evaluated comparing the pre-dilation and post-dilation scans. RESULTS: No statistically significant difference was found between pre-dilation and post-dilation measurements. There was a high pre-dilation to post-dilation correlation of 98%, 98%, 98%, 93%, and 95% for nerve fiber indicator, TSNIT average, TSNIT standard deviation, superior average, and inferior average, respectively. Less than 5% of the measurement variability was attributed to changes in pupil size (R2 ranging from 0.024 to 0.047). Stratifying the data by diagnostic groups yielded similar results. CONCLUSIONS: Pharmacologic mydriasis was not found to influence the retinal nerve fiber layer measurements acquired using the GDx-VCC. Results were comparable to scans achieved in the same eyes prior to dilation.

Aged↗
PubMed1999

Effects of tobacco smoking on the human pupil.

OBJECTIVE: Determine the effects of tobacco cigarette or sham placebo-smoking on pupil diameter. SUBJECTS: Ten non-smokers and 10 tobacco smokers (all healthy, drug free adults) were studied while resting in a comfortable lounger. METHODS: Tobacco smokers abstained from smoking and all subjects abstained from caffeine-containing products for at least 8 h prior to testing. The smokers each smoked one tobacco cigarette, and the non-smokers each inhaled air through an unlit sham cigarette. Right pupil diameter, heart rate, systolic and diastolic blood pressure were measured before and after sham- or tobacco-smoking in each subject. Pupil size was measured from a colored photograph taken with a Polaroid camera equipped with a high-speed flash with the subject in a standardized, dimly lit quiet room. RESULTS: There was no significant difference in baseline pupil diameter between non-smokers and smokers prior to sham- or tobacco-smoking. After sham- or tobacco-smoking, both non-smokers and smokers showed slight but statistically significant pupillary constriction. CONCLUSIONS: Shortly after smoking one tobacco cigarette, pupillary constriction was greater than after sham-smoking.

Adult↗