Effect Of Pupil Size Research Articles

Requirements for segmented correctors for diffraction-limited performance in the human eye

Wavefront correctors have yet to provide diffraction-limited imaging through the human eye's ocular media for large pupils (>/= 6 mm).To guide future improvements in corrector designs that might enable such imaging, we have modeled the performance of segmented piston correctors in conjunction with measured wave aberration data of normal human eyes (mean=34.2 yr; stdev= 10.6 yr). The model included the effects of pupil size and wavelength in addition to dispersion, phase wrapping, and number and arrangement of facets in the corrector. Results indicate that </= 100x100 facets are needed to reach diffraction-limited performance for pupils up to 8 mm (extrapolated) at 0.6 microm wavelength. Required facet density for the eye was found to be substantially higher at the pupil's edge than at its center, which is in stark contrast to the requirements for correcting atmospheric turbulence. Substantially more facets are required at shorter wavelengths with performance highly sensitive to facet fill. In polychromatic light, the performance of segmented correctors based on liquid crystal technology was limited by the naturally occurring longitudinal chromatic aberration of the eye rather than phase wrapping and dispersion of the liquid crystal. Required facets to correct defocus alone was found highly sensitive to pupil size and decentration.

The effects of pupil size on the multifocal electroretinogram

This is an investigation of the effect of changing the pupil diameter on the P1 amplitude and latency of the multifocal electroretinogram (mfERG). MfERGs were recorded using a custom built wide field electrophysiological system. An array of 61 empirically scaled hexagons was used to stimulate the visual field. The duration of overall recording period was 8 min, segmented into 16 intervals each lasting 30 s. A combination of mydriatics and miotics were used to pharmacologically alter the pupil size and diameters between 1 and 10 mm were measured. There was a reduction in mfERG P1 amplitude in some cases greater than 50% (mfERG P1 amplitude 53 nV at 8 mm to 25 nV at 1 mm), with a change in pupil diameter of 7 mm. The mfERG P1 latency increased in some cases by as much as 8 ms in the central 40 degrees (mfERG P1 latency 39 ms at 8 mm to 47 ms at 1 mm). These results suggest that pupil size has significant effects on mfERG P1 amplitude and latency.

Phakometric measurement of ocular surface radii of curvature, axial separations and alignment in relaxed and accommodated human eyes.

Measurements (autokeratometry, A-scan ultrasonography and video ophthalmophakometry) of ocular surface radii, axial separations and alignment were made in the horizontal meridian of nine emmetropes (aged 20-38 years) with relaxed (cycloplegia) and active accommodation (mean +/- 95% confidence interval: 3.7 +/- 1.1 D). The anterior chamber depth (-1.5 +/- 0.3 D) and both crystalline lens surfaces (front 3.1 +/- 0.8 D; rear 2.1 +/- 0.6 D) contributed to dioptric vergence changes that accompany accommodation. Accommodation did not alter ocular surface alignment. Ocular misalignment in relaxed eyes is mainly because of eye rotation (5.7 +/- 1.6 degrees temporally) with small amounts of lens tilt (0.2 +/- 0.8 degrees temporally) and decentration (0.1 +/- 0.1 mm nasally) but these results must be viewed with caution as we did not account for corneal asymmetry. Comparison of calculated and empirically derived coefficients (upon which ocular surface alignment calculations depend) revealed that negligible inherent errors arose from neglect of ocular surface asphericity, lens gradient refractive index properties, surface astigmatism, effects of pupil size and centration, assumed eye rotation axis position and use of linear equations for analysing Purkinje image shifts.

Effect of pupil size on visual function under monocular and binocular conditions in LASIK and non-LASIK patients

Purpose To compare binocular and monocular vision in patients treated with laser in situ keratomileusis (LASIK) and in non-LASIK patients. Setting Jules Stein Eye Institute, Los Angeles, California, USA. Methods This comparative cross-sectional study comprised 20 postoperative LASIK patients and 20 non-LASIK ametropic patients. LogMAR visual acuity, contrast sensitivity, and infrared pupillometry were tested. Outcome measures were better-eye monocular acuity, binocular acuity, better-eye contrast sensitivity, binocular contrast sensitivity, and pupil diameter under monocular and binocular conditions. Results Binocular visual acuity and contrast sensitivity were statistically significantly better than the visual acuity in the better eye ( P = .0047 to <.0001) in both patient groups. Pupil diameter was statistically significantly smaller under the binocular condition than the monocular condition ( P <.0001) in both groups. Conclusions Monocular testing induced larger pupil diameters, which was associated with reduced vision compared to binocular measurements in LASIK and non-LASIK patients.

The effect of pupil size on binocular summation at suprathreshold conditions

Purpose. To determine the influence of retinal illuminance on monocular or binocular visual reaction time (VRT). Methods. On two normal subjects, uniform circular stimuli were presented with respect to a reference stimulus at the fovea under suprathreshold conditions, and the detection of positive and negative luminance variations was recorded. Binocular and monocular reaction times were measured (by the index finger pressing on a mouse key) for viewing with both natural and artificial pupils. Results. Binocular reaction times were shorter than monocular reaction times; nevertheless, this binocular-summation effect was less marked in trials with the artificial pupil. Analyses of binocular-summation ratios for contrast changes for both pupil types indicated maximum and minimum binocular-saturation values depending on contrast variations in both positive and negative luminance changes. Conclusions. Binocular summation can be influenced by pupil size under suprathreshold conditions. Results are discussed in terms of retinal illuminance and cortical pupil response mechanisms.

A learner first, a child with autism second.

The image-forming properties of the human optical system have been examined with the aid of a photoelectric ophthalmoscope. The light distributions in images of bright vertical lines formed by a double passage through the eye optics were measured. On the assumption that the eye optics are reversible, the light distributions on the retina were computed by means of Fourier transforms. The results are also expressed in terms of the spatial frequency response functions for the eye. The effects of pupil size were examined. The best imagery was obtained with a 5-mm pupil. The results confirmed the earlier measurements on human eyes reported by Flamant. The more recent experiments on animal material by DeMott do not seem to be relevant to living human eyes.

Pupil-size effects in fiber optic stellar interferometry.

The effects of finite telescope pupil sizes on the measurement of fringe visibility in fiber optic stellar interferometry are described. It is shown theoretically that the measured fringe visibility is equal to the cross correlation of the magnitude of the source's mutual coherence function with the cross correlation of the telescopes' effective pupil functions. If the telescopes' effective pupil diameters are not small compared with the width of the source's mutual coherence function, then the measured fringe visibility will be correspondingly distorted. The theoretical results are verified experimentally in a fiber optic Mach-Zehnder interferometer.

Pupil size, mean accommodation response and the fluctuations of accommodation

We wished to determine how pupil size and mean accommodation response level interact to influence the fluctuations of accommodation. A dynamic infra-red optometer was used to record accommodation responses while subjects viewed a steady target at two stimulus levels (1.5 and 3 D) through four pupils (1, 2, 4 and 6 mm). It was found for most subjects that the fluctuations of accommodation increase at higher mean accommodation response levels, and small pupils lead to an increase in the low frequency (but not the high frequency) fluctuations of accommodation. The effects of mean accommodation response are independent of pupil size, and the effects of pupil size are independent of mean response level.

Effect of pupil size and astigmatism on contrast acuity with monofocal and bifocal intraocular lenses

We conducted a bicenter study to evaluate the effect of pupil size and corneal astigmatism on best corrected contrast acuity (BCCA) in patients with the True Vista™ bifocal intraocular lens (IOL) and compared the results with those in a matched group of monofocal patients. Best corrected contrast acuity was measured using the Regan Charts (96%, 50%, 25%, 11 %) at four pupil sizes (2.0, 2.5, 3.5, 6.0 mm) in three groups (Group 1: corneal astigmatism 0–0.50 D [n = 11]; Group 2: 0.75–1.50 D [n =11 ]; Group 3: 1.75–2.50 D [n = 4]). In monofocal eyes, BCCA between these astigmatic groups did not differ significantly at any contrast step or at any pupil size tested. However, BCCA decreased slightly with increasing pupil size in each group, and differences between 2.0 mm and 6.0 mm pupils were significant at each contrast level. In all bifocal groups, BCCA decreased significantly with increasing pupil size and also decreased with increasing corneal astigmatism; differences were significant at most pupil sizes and contrasts tested. In Group 1, BCCA was lower in eyes with bifocal IOLs than in eyes with monofocal IOLs at 25% and 11 % contrast with a 2.5, 3.5, and 6.0 mm pupil; with a 2.0 mm pupil it did not differ significantly. In Groups 2 and 3, BCCA in eyes with bifocal IOLs was lower at all contrast steps and all pupil sizes tested. Our results indicate that corneal astigmatism in excess of 0.50 D reduces quality of vision in eyes with bifocal IOLs, while eyes with monofocal IOLs are not affected. It may be important to minimize postoperative corneal astigmatism in patients with bifocal IOLs.

Subjective and Objective Assessment of Soft Bifocal Contact Lens Performance

Subjective and objective techniques were used to assess the on-eye performance of soft bifocal contact lenses. In the subjective technique a young observer whose accommodation had been paralyzed with a cycloplegic agent was fitted with the contact lens type under investigation and aligned with a Maxwellian view Badal optometer using a bite-bar. Visual acuity was measured as a function of both target vergence (0.00 to -4.00 D) and pupil size (1 to 5 mm). Aspheric, concentric, and diffractive soft bifocal contact lens designs were investigated. Diffractive and concentric bifocal designs with +2.00 D near additions showed "twin peaks" of visual acuity with one peak at 0.00 D target vergence (equivalent to distance viewing) and the second at -2.00 D target vergence (equivalent to a target at 50 cm). Some aspheric designs produced a relatively constant visual acuity across this vergence range, whereas others gave poor acuity at near. Visual acuity with the Echelon diffractive lens was relatively unaffected by pupil size, confirming theoretical predictions. Visual acuity with concentric designs was also relatively free of pupil size effects. In the objective technique, the variation in surface power across the lens was assessed using video-keratography. This technique provided an elegant means of visualizing the power profile of the lens. The location of the zones of increased power and the magnitude of power variations allowed an accurate prediction of the visual performance measured subjectively. Temporal displacement of lenses may explain the occasions where visual performance did not vary with pupil size.

The effect of pupil size on chromostereopsis and chromatic diplopia: Interaction between the Stiles-Crawford effect and chromatic aberrations

Several studies have reported that the magnitude of chromostereopsis changes as the pupil size changes. Einthoven's theory, that chromostereopsis is determined by interocular differences of monocular transverse chromatic aberration, can not easily explain this change. Therefore, several alternative hypotheses have been introduced, most notably by Vos [(1960) Vision Research, 6, 105-107], who argues that shifts in chromostereopsis with pupil size are due to decentration of the peak of the Stiles-Crawford effect (SCE) with respect to the pupil. We tested this hypothesis by measuring chromostereopsis under both scotopic (no SCE) and photopic conditions with centered and decentered artificial pupils. The results show that the SCE plays an important role in the effect of pupil size on chromostereopsis. Similar changes were also measured in monocular chromatic diplopia which supports the hypothesis that the effect of pupil size on chromostereopsis is due to monocular mechanisms.

Calculations of two-dimensional foveal retinal images in real eyes

Foveal point-spread functions are computed from experimental wave-aberration data for individual emmetropic subjects. The effects of pupil size and image focus are considered in the calculations. Foveal images of extended test objects are generated from the point-spread functions corresponding to different image-quality situations. Wiener-filtered test objects are also computed to obtain a partial compensation of the spatial degradation introduced by the eye's optical system in the visual process.

The effect of pupil size on static and dynamic measurements of accommodation using an infra-red optometer.

The study examines to what degree the output of the Canon Auto-ref R1 infra-red (IR) optometer is affected by variations in pupil size for both static measurement of refractive error and for continuous recording of accommodation when switched to its modified mode of operation. In the normal static mode of operation the measurement of refractive state simply depends on the position of the peak photodetector output for each of three meridians: it does not depend on signal amplitude and hence pupil size. However, in continuous mode the actual output of a single photodiode is measured and the measurement is susceptible to changes in pupil size that occur within the area of the exit pupil utilized by the instrument. Using static and dynamic recording on model and human eyes the study shows that a 10% reduction in output signal relative to the maximum output level (for a constant stimulus) occurs for pupil sizes of 3.9 mm. The relatively small exit pupil has important advantages with regard to the use of mydriatic drugs and task-induced changes in pupil diameter.

Effect of pupil size on kinetic visual field measurements

We determined visual field size as a function of pupil size by repeated measurements of Goldmann fields with an I2 target in the same subjects using contact lenses with different sized artificial pupils. Increasing pupil size from 3 to 6.8 mm increases visual field size from 2.79 to 3.34 steradians, an average increase of 19.7 per cent; a control experiment suggested that the major part of this effect can be explained by reduction of retinal illuminance produced by the variation in pupil size.

Phase-transfer function of the human eye and its influence on point-spread function and wave aberration.

The bidimensional phase-transfer function (PTF) of the human eye has been computed from aerial retinal images of a point test. These images were previously determined by using a recently developed hybrid optical-digital method. Actual PTF data have been obtained directly without linear variations with spatial frequency and have shown great variations among individual subjects. The influence of the PTF on the determination of the point-spread function and the wave-aberration function for emmetropized and slightly astigmatic subjects has been also evaluated. Finally, the effect of pupil size on the PTF was determined by computing these functions from the wave aberration. These results allow us to give a more thorough description of the optical image quality of the human eye and can be used as actual data in subsequent psychophysical studies.

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.

Relationship Between Refractive Error and Visual Acuity in the PERK Study-Reply

In Reply. —In our study, we noted that for eyes with a cycloplegic refraction in the range of -2.00 to -2.50 D, the average uncorrected manifest visual acuity of eyes undergoing RK (20/63) was better than the average visual acuity of unoperated-on eyes (20/125). We agree with Dr Applegate and Mr Jones that one possible explanation for this observation is that we measured cycloplegic refraction with the pupil dilated and uncorrected visual acuity with the pupil in its normal state. The possible effect of pupil size was discussed at length in the section entitled Diameter of the Pupil. As stated in the article, after RK, the paracentral cornea flattens less than the central cornea, beginning at the edge of the central clear zone. This may produce a slight increase in refractive myopia when the pupil is dilated. Therefore, after RK, the uncorrected visual acuity may be better than that suggested

Effect of pupillary dilatation in flash VER testing.

Light flash transient visual evoked response (VER) testing is often a part of the perioperative evaluation of eyes with opaque media, and pupillary size in these patients may not be knowable or may be inadvisable to alter. We therefore evaluated transient light flash VER responses before and after pupillary dilation in normal controls and in patients with media opacities to evaluate the effects of pupil size on the amplitude and latency of the recorded VER. Monocular testing was performed bilaterally with a Grass PS-22 photostimulator at the S1 and S16 settings, with monopolar recordings 1 cm above the inion. One hundred twenty-eight 200-msec samplings were recorded and averaged on a Nicolet CA-1000 clinical averager. Latencies were often shorter with the stronger light stimulus, but pupillary dilation did not produce a clear trend toward shorter latencies. Overall, pupillary dilatation did not significantly increase recorded amplitudes, nor did iris color appear to be a factor. These results suggest that, under our testing conditions, pupillary dilatation is not necessary for obtaining reliable transient flash VER recordings.

Pupil size in relation to ultrasonic anterior chamber depth measurements in pseudophakic eyes

The effect of pupil size on ultrasonically determined anterior-chamber depth was studied in vitro with the Storz Alpha 20/20 and with the Kretz ultrasonoscope at high and low system sensitivity. The traces were measured peak to peak and base to base; results were compared to anterior-chamber depth measurements with optical pachymetry. We conclude that when measuring anterior-chamber depth with ultrasound, the pupil must be fully dilated or reduced system sensitivity must be used and the traces measured peak to peak.

Modification of pattern reversal VERs by ocular accommodation

The amplitudes and implicit times of the P-1 component of monocular transient pattern VERs elicited by reversing checkerboard targets were measured in 6 conditions: (1) Ocular accommodation (Ao) elicited by minus power ophthalmic lenses; (2) Ao stimulated by minus lenses with the natural pupil of the test eye dilated and replaced by an artificial pupil; (3) accommodative demand and pupil size fixed with retinal image size (I r) changed by afocal minifying lenses, (4) accommodative demand andI r fixed but pupil size changed; (5) Ao elicited by minus lenses for three sizes of reversing checkerboards, and (6) Ao elicited by minus lenses for a constant checkerboard size with three check sizes. The observed decrease in VER amplitude with Ao could not be attributed entirely to the effects of pupil size orI r. The rate at which the amplitude of P-1 decreased with Ao was not affected by checkerboard check size, but was closely correlated with checkerboard field size. The implicit time of P-1 first decreased slightly below baseline values at low and moderate levels of Ao and then tended to increase significantly at higher levels. The increase in implicit time at high levels of Ao could be explained adequately by the effects of pupil size alone on the VER. However, where Ao occurred without pupillary miosis, the increase in implicit time could only be explained by focusing error.