Amplitude of accommodation and refractive error

This paper investigates the amplitude of accommodation of early onset myopes, late onset myopes, emmetropes, and hyperopes. Eighty subjects were used, 41 women and 39 men, with an age range of 18-22 yr (mean = 19.82). All subjects wore an optimum refractive correction, giving visual acuities of 20/20 or better. Significant differences were found between the four refractive groups, with late onset myopes having the largest amplitude of accommodation, followed by early onset myopes, emmetropes, and hyperopes. The results are discussed in the light of previous findings on tonic accommodation and the accommodative response gradient and interpretated in the context of a dual innervation to the ciliary muscle.     

Amplitude of accommodation and its relation to refractive errors

AIMS: To evaluate the relationship between amplitude of accommodation and refractive errors in the peri-presbyopic age group. MATERIALS AND METHODS: Three hundred and sixteen right eyes of 316 consecutive patients in the age group 35-50 years who attended our outpatient clinic were studied. Emmetropes, hypermetropes and myopes with best-corrected visual acuity of 6/6 J1 in both eyes were included. The amplitude of accommodation (AA) was calculated by measuring the near point of accommodation (NPA). In patients with more than +/- 2 diopter sphere correction for distance, the NPA was also measured using appropriate soft contact lenses. RESULTS: There was a statistically significant difference in AA between myopes and hypermetropes (P < 0.005) and between myopes and emmetropes (P < 0.005) in the 35-39 year age group. In the 40-44 year age group, there was a significant difference in AA between emmetropes and hypermetropes (P < 0.0001), emmetropes and myopes (P < 0.01) and hypermetropes and myopes (P < 0.0001). In patients above 45 years of age there was no significant difference (P > 0.5). CONCLUSION: Our study showed higher amplitude of accommodation among myopes between 35 and 44 years compared to emmetropes and hypermetropes.     

Frequency characteristics of accommodation in a patient with agenesis of the posterior vermis and normal subjects

AIMS—To clarify the cerebellar control of accommodation in humans, the frequency characteristics of accommodation were studied in a patient with agenesis of the posterior cerebellar vermis and four age matched normal subjects.
METHODS—Magnetic resonance imaging of the brain of the 29 year old patient showed agenesis of the vermis and paravermis of lobules VIII-X and hypoplasia of the vermis and paravermis of lobules I-VII, the cerebellar hemisphere, and the cerebellar nuclei. The gain and phase lag of accommodative responses for sinusoidally modulated blur stimuli were calculated for the patient and four normal subjects. The blur stimuli consisted of predictable simple sinusoids of 3.0 dioptres at a frequency of 0.05, 0.1, 0.2, 0.3, 0.5, or 1.0 Hz.
RESULTS—The frequency characteristics of accommodative responses in the patient have a larger phase lag and a smaller gain at higher frequencies than those in the four normal subjects.
CONCLUSIONS—These findings suggest that the cerebellum contributes to the control of accommodation by improving the frequency characteristics at high frequencies.

     

The effect of modulating ocular depth of focus upon accommodation microfluctuations in myopic and emmetropic subjects

The magnitude of accommodation microfluctuations increases in emmetropic subjects viewing low luminance targets or viewing a target through small artificial pupils. Larger microfluctuations reported in myopia may result from an abnormally large depth of focus (DoF). The effect of modulating the size of the DoF has not been investigated in myopic subjects and may help to explain the cause of the increased DoF. Accommodation microfluctuations were recorded under two experimental conditions. Firstly, 12 emmetropes (EMMs), and 24 myopes (MYOs) viewed a Maltese Cross target with luminance levels of 0.002, 0.2, 6 and 600 cd/m² and in darkness, and second, 14 EMMs and 16 MYOs viewed a Maltese Cross target through pupil diameters of 0.5, 1, 2, 3, 4 and 5 mm presented in Maxwellian view. The magnitude of the accommodation microfluctuations increased significantly with a target luminance of 0.002 cd/m² (p < .03) and pinhole diameters of <2 mm (p < .05). For all other luminance levels and pupil diameters the magnitude was constant. For both conditions, MYOs had significantly larger microfluctuations than EMMs (p < .01). Considerable inter-subject variability was observed in the degree to which the magnitude of the microfluctuations increased, for both the 0.002 cd/m² luminance and 0.5 mm pupils, however, this was not correlated with refractive error. The increase in the magnitude of the microfluctuations while viewing a low luminance target (0.002 cd/m²) may be due to a shallower contrast gradient in the cortical image, with a consequent increase in DoF. The microfluctuations also increase when viewing through small pupils (<2 mm), which increases the DoF without altering the contrast gradient. The larger microfluctuations found in the MYOs consolidates the theory that MYOs have a larger DoF than EMMs and therefore have a higher threshold for retinal image blur.     

Short-term effects of low-concentration atropine eye drops on pupil size and accommodation in young adult subjects

Graefe's Archive for Clinical and Experimental Ophthalmology - A single eye drop containing 0.01% atropine every evening has previously been found to inhibit myopia progression in young adults....     

Fatigue of accommodation: changes in accommodation after visual work

The present study was designed to determine whether classical accommodation theory or dual-innervation accommodation theory best explains the visual fatigue effects of prolonged visual work. The accommodation responses of 20 young male adults were measured, using a laser optometer, while they viewed a near target (30 cm), a far target (6 m), or in total darkness. Measurements were made before and after 1-h fatigue sessions, during which subjects either read monocularly presented slides of text at near or far distances, or remained in darkness. There were no significant changes in near or far target static accommodation as a result of any of the fatigue sessions. Dark focus accommodation shifted inward after the near target viewing task and after prolonged dark viewing. The results are discussed in terms of their implications for research in accommodative fatigue, and their relation to other current research.     

Refractive group differences in accommodation microfluctuations with changing accommodation stimulus

PURPOSE: Microfluctuations of accommodation are known to increase in magnitude with increasing accommodation stimulus. Reduced sensitivity to blur in myopic subjects could also lead to increases in the magnitude of the microfluctuations. The aim of this study is to examine the effect of variations in accommodation stimulus upon the microfluctuations in different refractive groups. METHODS: Thirty-six subjects were divided into three groups depending upon their refractive error and age of onset of their myopia; 12 emmetropes (EMMs), 12 early onset myopes (EOMs) and 12 late-onset myopes (LOMs). Steady-state accommodation responses were recorded continuously for 2 min using the Shin-Nippon SRW-5000 autorefractor at a sampling rate of 52 Hz while viewing targets at accommodation stimuli levels of 0, 1, 2, 3 and 4 D in a Badal (+5 D) optical system. RESULTS: The EMMs and EOMs showed systematic increases in the root mean square (r.m.s.) value of the microfluctuations with increasing accommodation stimulus. In contrast, no systematic variation with accommodation stimulus was found for the LOMs. Power spectrum analysis demonstrated that increases in the size of the microfluctuations were mediated by increases in the power of the low frequency components of the accommodation response. CONCLUSIONS: The magnitude of the microfluctuations in the EMMs and EOMs may be influenced primarily by accommodation response-induced zonular relaxation effects or to changes in the physical properties of the accommodation plant with increasing accommodation response. The LOMs may have an increased baseline neural blur threshold, which appears to modulate the magnitude of the accommodative microfluctuations for low accommodation levels. At higher accommodation demands, the changes in the physical properties of the accommodation plant or the zonular relaxation effects appear to exceed the blur threshold, and the known association between microfluctuations and accommodation stimulus level is restored.     

Objective accommodation parameters depending on accommodation task

62 myopic patients were examined to study objective accommodation parameters in different conditions of accommodation stimulus presenting (use of convex lenses). Objective accommodation response (OAR) was studied using binocular open-field autorefractometer in different conditions of stimulus presenting: complete myopia correction and adding of convex lenses with increasing power from +1.0 till +3.0 D. In 88,5% of children and adolescents showed significant decrease of OAR for 1,5-2,75D in 3.0D stimulus. Additional correction with convex lenses with increasing power leads to further reduce of accommodation response. As a result induced dynamic refraction in eye-lens system is lower than accommodation task. Only addition of +2,5D lense approximates it to required index of -3.0D.     

Restoration of accommodation

PURPOSE OF REVIEW: This review examines the current status of accommodation restoration concepts with reference to the recent, published peer-reviewed literature with an emphasis on physiological aspects of accommodation and presbyopia. RECENT FINDINGS: The mechanisms of accommodation and the causes of presbyopia are described. The physiological amenability of the accommodative structures in the presbyopic eye to accommodation restoration is discussed. General theoretical concepts of accommodation restoration are introduced. The methods that have been used to assess accommodation restoration, including the use of animal models, drug stimulated accommodation, subjective near-vision tests and objective measurements, are reviewed. SUMMARY: While physiological and clinical evidence supports the notion that accommodation can be restored to the presbyopic eye, progress in this potentially exciting area is hindered by the scarcity of good, large-scale clinical studies using objective measurement techniques to evaluate the outcomes of accommodation restoration concepts.