Static Accommodative Responses Research Articles

Effect of phenylephrine on static and dynamic accommodation

PurposeWe tested the hypothesis that changes in accommodation after instillation of Phenylephrine Hydrochloride (PHCl) observed in some studies could be caused by changes in optics. MethodsWe performed two experiments to test the effects of PHCl on static and on dynamic accommodation in 8 and 6 subjects, respectively. Objective wavefront measurements were recorded of the static accommodation response to a stimulus at different distances or dynamic accommodation response to a sinusoidally moving stimulus (between 1 and 3 D of accommodative demand at 0.2Hz). The responses were characterized using two methods: one that takes into account the mydriatic optical effects on the accommodation produced by higher-order aberrations of the eye and another that takes into account only power changes paraxially due to the action of the ciliary muscle and regardless of the pupil size. ResultsWhen mydriatic optical effects were taken into account, differences in responses before and after PHCl instillation were 0.51±0.53 D, and 0.12±0.15, for static and dynamic accommodation, respectively, and were statistically significant (p<0.039). When mydriatic optical effects were not taken into account, the differences in responses before and after PHCl instillation were −0.20±0.51 D, and −0.05±0.14, for static and dynamic accommodation, respectively, and were not statistically significant (p>0.313). ConclusionsThe mydriatic effect of the PHCl causes optical changes in the eye that can reduce the objective and subjective measurement of accommodation.

A randomised clinical trial to assess the effect of a dual treatment on myopia progression: The Cambridge Anti‐Myopia Study

To evaluate the effect of a dual treatment modality for myopia, by improving accommodative functions, on myopia progression. A double blind randomised control trial was conducted on 96 subjects. The treatment modality for the trial employed custom designed contact lenses which control spherical aberration in an attempt to optimise static accommodation responses during near-work, and a vision-training programme to improve accommodation dynamics. Myopia progression was assessed over a 2 year period using cycloplegic autorefraction and biometry. The mean progression was found to be -0.33 Dioptres (D) over the 2 years of the study. There was no interaction between contact lens treatment and vision training treatment at 24 months (p = 0.72). There was no significant treatment effect of either Vision Training or Contact Lens Spherical Aberration control on myopia progression. This study is unable to demonstrate that the progression of myopia can be reduced over a 2 year period by either of the two treatments aimed at improving accommodative function. Neither treatment group (contact lens or vision training) progressed at a slower rate over the 2 years of the study than did the appropriate control group.

The effects of spherical aberration on static accommodative responses in emmetropes and myopes

To compare the effects of spherical aberration (SA) on accommodative responses between emmetropes (EMs), stable myopes (SMs), and progressing myopes (PMs). The accommodative responses (AR) induced by negative lenses from 0 to -5 D in 1 D steps were measured with a Complete Ophthalmic Analysis System (COAS) for 10 emmetropes (EMs), 13 stable myopes (SMs), and 9 progressing myopes (PMs). Three types of AR were calculated from wavefront aberration data based on ocular foci within a paraxial area, natural pupil area, and a 3.5 mm-diameter annular pupil area. The accommodative stimulus response curves (ASRCs) were compared between the three groups and between the three AR conditions. The difference in the slope of ASRC was significant between the three AR conditions (p < 0.0001) but it was not significant between the three refractive groups. In each group, the slope of ASRC for the accommodative response measured within the paraxial area of the pupil (paraxial AR) was significantly steeper than that measured for the natural pupil (total AR) and also for that estimated for the 3.5 mm-diameter annular pupil (p < 0.01). The difference in the y-intercept of ASRC between the three AR conditions was also significant (p = 0.02) but not between the three refractive groups. The y-intercept of ASRC for paraxial AR was more positive than that for total AR in SMs (p < 0.01) and in PMs (p < 0.05); the y-intercept of ASRC for the 3.5 mm peripheral AR was more positive than that for total AR in SMs (p < 0.05). The spherical aberration of the eye has a significant effect on the slope of ASRC and is less in PMs than in EMs and SMs.

Static accommodative responses following adaptation to differential levels of blur

To investigate the effects of two levels of blur adaptation on visual resolution and steady-state accommodation responses in emmetropes and myopes. Eleven emmetropes (mean refractive error +0.01 +/- 0.31 DS) and 11 early-onset myopes (EOM, mean refractive error -4.44 +/- 1.64 DS) fixated monocularly at 4 m in three trials of 45 min duration with either: optimal refractive correction, +1 DS defocus, or +3 DS defocus. Monocular logMAR visual acuity (VA) was measured at 10 min intervals during each trial, and immediately following completion of the trial. Accommodative stimulus-response function (ASRF), refractive error and pupil size were measured before and after each trial. Blur adaptation was found to have no effect on pupil size or baseline refraction, irrespective of the power of the blurring lens. Adaptation to +1 DS of defocus yielded an improvement in VA of -0.16 +/- 0.07 logMAR and -0.17 +/- 0.11 logMAR in the emmetropes and myopes respectively. An improvement in VA of -0.20 +/- 0.18 logMAR in the emmetropes and -0.26 +/- 0.17 logMAR in the myopes was observed following adaptation to +3 DS of defocus. The changes in acuity became significant following 30 min of exposure to defocus. Blur adaptation was found to have no effect on the ASRF gradient or individual steady-state accommodative responses. Following blur adaptation, visual resolution was found to increase in both emmetropes and myopes. The magnitude of the blur level did not produce significantly different increases in resolution. Blur adaptation failed to affect either the steady-state responses to an accommodative stimulus or ASRF gradient.

Oculomotor adaptations produced by virtual reality environments

Purpose: Virtual reality (VR) displays require a static accommodation response to be maintained despite continual variation in vergence. The aim of this experiment was to establish the effect of VR stimulation upon the tonic elements of the accommodation and vergence controllers.Methods: Twenty subjects (mean age 22.0 ± 4.5 years) participated with informed consent in the experiment. The subjects were emmetropic and free of all ocular or systemic disease. Tonic accommodation (TA) was measured in darkness using the Shin‐Nippon SRW‐5000 (Tokyo, Japan) infrared autorefractor which takes a measure of the accommodative state every 1 s. Readings were taken over a period of 3 min and an average TA value was calculated when the accommodative state had reached a stable level. Tonic vergence (TV) was measured in darkness continuously for 3 min using an EyeTrace 300X (Iota AB, Sundvall, Sweden) infrared limbal eyetracker and an average TV value was calculated when the traces had reached a stable level. Subjects were then immersed in a VR environment, for 30 min, generated using SimulEyes field‐sequential shutter goggles controlled by a Dell XPS R450 PC (Bracknell, UK). The VR display required a constant accommodation response of 3D, while the vergence response typically varied between 0 and 5 MA. Following immersion, measurements of TA and TV were repeated.Results: A significant relationship (y = 1.13x − 0.71, R = 0.85, p = 0.001) was found between the initial TV level and the shift induced by the VR environment such that negative TV positions shifted in the positive direction and vice‐versa. No significant change in TA was observed.Conclusions: The VR environment produced substantial adaptation of TV. These findings suggest that the vergence controller acts to shift vergence bias in order to reduce stimuli conflicts with accommodation found in VR environments. This enables subjects to maintain a stable accommodation response despite continual changes in the vergence position.

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.

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 49years shows that the slope of the curve reduces only slowly with age up to about 40years 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.

An infrared eccentric photo-optometer.

An objective infrared optometer has been designed, based on the optical principles of eccentric photorefraction. A CCD camera with an eccentric infrared light source images the subject's pupil through a Badal optometer. The slope of the light distribution across the pupil is continuously recorded. Accommodative state is measured by moving the camera behind the Badal lens until the slope is zero. This position corresponds to the case where the camera is conjugate with the retina of the observer. In this Badal optometer, the irradiance of light at the pupil plane, the sensitivity of the photorefractor, and the focal setting of the camera lens remain constant for all positions of the camera from the eye. The repeatability of a single measure of refractive state in a cyclopleged eye was less than 0.05 D. Static accommodative responses taken from 3 subjects in both closed and open loop conditions provided expected stimulus/response measures. The instrument can also be adapted to measure dynamic accommodation.

Accommodation and flicker: evidence of a role for temporal cues in accommodation control?

Static accommodation responses to sinusoidal grating stimuli that displayed temporal modulations in luminance contrast (i.e. contrast flicker) were measured with a laser speckle optometer. The effects of a variety of temporal waveforms were investigated including square-wave modulations, sinusoidal modulations, and band-pass filtered noise. The effects of altering both the amplitude and the temporal frequency (0.4-30 Hz) of the contrast flicker and the spatial frequency of the stimulus (0.77-9.2 c/deg) were also examined. All the flicker waveforms investigated (square wave, sinusoidal and band-pass noise) reduced accommodative accuracy, the effect being most apparent at lower spatial frequencies (0.77-1.15 c/deg). With band-pass filtered noise the effects of flicker were most apparent with frequencies in the range 1-4 Hz, at both lower (0.4 Hz) and higher flicker frequencies (8-32 Hz) accommodations was less affected. It was found that flicker impaired accommodation under conditions where the contrast was at all times suprathreshold. This is incompatible with the proposal that flicker reduces accommodation responses because for part of each flicker cycle the stimulus was below threshold. However, these results are compatible with the alternative hypothesis that flicker impairs the ability of the accommodation system to utilize temporal cues such as those derived from the higher frequency component (1-2 Hz) of accommodative oscillations.

A longitudinal study of the changes in the static accommodation response

The results are described of a 10-year study of the longitudinal changes in the static response of an individual subject during the approach to absolute presbyopia. The amplitude of accommodation declines linearly with age. A new finding is that the magnitude of the slope of the linear portion of the response/stimulus curve also reduces with age, as does the level of tonic accommodation.

EFFECTS OF 0.1% CYCLOPENTOLATE OR 10% PHENYLEPHRINE ON PUPIL DIAMETER AND ACCOMMODATION

The mydriatic and cycloplegic effects of either one drop of 0.1% cyclopentolate or two drops of 10% phenylephrine were studied over a period of up to 6 hours after drug instillation, using 5 subjects aged between 25 and 43 years. The extent of mydriasis was determined from the horizontal diameter of the pupil. Dynamic accommodation responses were monitored with an infra-red, continuously recording optometer. Static measurements of the accommodation response/stimulus curve were made with a laser optometer. With either drug, dilation of the pupil occurred more rapidly than recovery of normal pupil diameter. Both drugs caused alterations in the dynamic and static accommodation responses. Response times were generally slowed, and the slope of the accommodation response/stimulus curve and the amplitude of accommodation were reduced. The time course of these changes was broadly similar to that of the pupil dilation. Cyclopentolate hydrochloride was more efficient as a mydriatic but exercised a greater unwanted cycloplegic effect.

ORTHOPTIC EFFECTS ON ACCOMMODATION AND RELATED VISUAL FUNCTIONS IN AN ADULT ALTERNATING ESOTROPE

Orthoptic therapy was instituted in an adult, alternating esotrope with asthenopia who exhibited inaccurate static accommodative responses with adequate, clinically determined, accommodative facility. During and following therapy the patient showed considerable improvement in accommodative accuracy and related visual functions, such as contrast sensitivity, in the absence of any change in strabismic deviation. This case provides the first laboratory documentation of orthoptic effects on accommodation in an adult strabismic.

Model of static accommodative behavior in human amblyopia.

When a target is moved from far to near, the normal accommodative system responds by changing the crystalline lens power until the blur of the retinal image is reduced to an acceptable level for clear vision. This feedback mechanism, along with the experimentally derived deadspace operator (representing the depth of field), forward-loop gain, and tonic accommodative bias level have been successfully incorporated into a static model of the normal accommodative system. We extended this model to the investigation of static accommodative responses in amblyopic eyes. The experimentally derived accommodative controller gain of the amblyopic eye was typically smaller than in the fellow dominant eye. In addition, the experimentally derived depth of field was increased in most amblyopic eyes, while the accommodative bias showed no consistent difference between the two eyes. The decrease in accommodative controller gain and increase in depth of field were sufficient to account for the reduction of accommodative responses found in amblyopic eyes. Theoretically, the model provides a conceptual framework for understanding the static accommodative deficits found in amblyopic eyes. Practically, the accommodative controller gain parameter provides a means for uniform assessment of normal and abnormal accommodative function, both experimentally and in the clinic environment.