# Accommodation and convergence relationship memes

AA: Amplitude of accommodation, MS Eq.: 'Main Sequence' relationship regression .. W. Yuan, P. MunozDynamic details of disparity convergence eye movements simultanee de la refraction et de l'acuite visuelle meme chez les le illettres. Accommodation-convergence relationships and age. Bruce AS(1), Atchison DA, Bhoola H. Author information: (1)Centre for Eye Research, School of Optometry. The eyes have a reflex action called the accommodation-convergence reflex which means that when your eyes converge to look at a close.

Although a single index approach 30 to describe the static accommodation response has been proposed by some researchers, we did not use this because it is not applicable to nonlinear regions of the ASR curve Fig. Data of a representative subject are shown by the solid curve in Figure 2. The linear portion of the ASR curve was used to determine the slope and the intercept.

**The accommodation reflex**

An objective method was used to determine the linear portion of the function instead of relying on visual inspection. A third-order polynomial was fit to the data, and the first derivative was computed Fig. The ASR data range, which yielded slope values greater than 0. Fitting higher order polynomials to this linear data did not produce better fits than the linear regression line. Therefore, the slope and intercept of this straight line estimated the gain and bias of the accommodation response.

### Accommodation-convergence relationships and age.

The distance in diopters between the data corresponding to the 0. The near point of accommodation NPA; maximal accommodation was estimated by the accommodation response corresponding to a derivative of zero at the peak of the ASR function. Pretreatment, posttreatment, and recovery data were analyzed separately.

Plots were of absolute values of accommodation and convergence with reference to primary position and the distance refractive correction. Linearity was assessed by visual inspection, because a single objective criterion could not be applied to determine linearity resulting from the variability in the data.

Fitting higher order polynomials to the linear portion of the data did not improve the fit, suggesting that the data do not violate the linearity assumption.

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Convergence bias indicates the open-loop convergence response when the accommodation response is zero. Similarly, the accommodation bias indicates the open-loop accommodation response when the convergence response is zero. The between-subjects factor was the subject group two levels, younger and older age groups.

A significant interaction effect between the two factors suggested that the changes from pretreatment data are different in the two groups. An absence of significant interaction effect and within-subjects effect indicated that reading glasses did not change the baseline data in either group. A sample size of 15 per group was chosen based on computations using pilot results. For an assumed alpha value of 0.

ASR slope estimates and sensitivity were similar with both 1- and 0. Accommodative amplitude was also defined with respect to true optical infinity NPA-0 D; i. This result was not attributed to one or two aberrant subjects. Twelve of 15 of the younger subjects and 14 of 15 subjects in the older groups displayed a reduction of accommodation.

Average changes in accommodative amplitude posttreatment were 0. Because the adaptive changes to reading spectacles were age-invariant, the accommodative amplitude data of the two age groups were combined for further analysis. As can be predicted from the hyperopic shift of the ASR intercept with treatment Fig. Discussion The impact of short-term use of reading spectacles on accommodative amplitude and the interactions between accommodation and convergence were studied in pre-presbyopia and incipient presbyopia.

The main findings are that wearing single-vision reading spectacles for 2 months induced distal shifts of the near and far points of accommodation without changing the range of accommodation in both groups.

The receded NPA did not recover to baseline after 2-month use of reading spectacles was discontinued, and this effect was independent of the age of the subjects studied.

The evidence was insufficient to suggest adaptation of the cross-links between accommodation and vergence. Adaptation of the Accommodation Stimulus-Response Function The ASR function depicted in Figure 2 illustrates that an increase or a decrease in accommodative amplitude can result primarily from vertical shifts biases of the accommodative response for distance 0 D stimuli, increases or decreases in the linear portion of the ASR function, changes in the slope of the ASR curve, or a combination of all three.

The results demonstrate that the accommodative amplitude estimated with respect to optical infinity declined after treatment with reading spectacles. Mean decreases in the amplitudes were 0.

It is apparent from the results that the slope of the ASR function did not change in either group after reading spectacles were worn Fig. However, the y-intercepts of the ASR function and the near point of accommodation were reduced after treatment in both groups.

The mean amplitude of the linear range of accommodation was constant after treatment in both groups. Therefore, by elimination, the main factor that appears to contribute to the decline in the accommodative amplitude of the two groups is the hyperopic shift of the ASR curve after treatment.

Figure 7 is a diagrammatic representation of the adaptive changes to the ASR curve after treatment. We propose that the NPA may normally be enhanced by a tonic bias of accommodation that elevates the entire ASR function and produces a myopic refraction bias. When this bias relaxes after the use of near spectacles, a hyperopic shift in the refractive state occurs, as does a reduction in NPA, specified from optical infinity, but the accommodative amplitude specified from the empiric far-point refraction is unaffected.

That there exists a tonic bias of accommodation is well established, as is its amenability to adaptation. Exposure to myopic defocus with plus lenses during distance fixation increases the subjective tolerance level to blur. Normally, presbyopic eyes show gradual hyperopic shifts, perhaps because of an age-related decrease in the gradient refractive index of lens.

As shown by the error bars in Figure 3Bthere was intersubject variability in the amounts of the hyperopic shifts, and this perhaps could be attributed to the differences in the baseline tonic innervation between subjects 34 35 or to the differences in the number of hours of near spectacle lens wear between subjects. It is also evident from our results that the NPAs receded by the same magnitude in emmetropes and myopes after treatment.

McBrien and Millodot 34 studied the adaptation of tonic accommodation in four different refractive groups.

They found that subjects with late-onset myopia experienced large increases in tonic levels after a minute period of sustained near activity, subjects with hyperopia experienced large counteradaptive effects opposite in sign to the accommodative stimulusand subjects with emmetropia and early-onset myopia fell in the middle and behaved in a similar manner.

In the present study, A striking feature of the present study is that we found no age-dependent adaptability of accommodative amplitude to reading spectacles. What implications do these findings have for the progression of presbyopia? If increased tonic activity of accommodation is not sustained during the wearing of reading spectacles, it could result in a reduction of NPA and the amplitude of accommodation.

The results also suggest that a myopic shift may normally slow down the progression of presbyopia by increasing the near point of accommodation. In the present study, subjects wore the reading spectacles only for near work so that conflicts between accommodative and convergence stimuli were not present when the reading glasses were not worn. There was no objective way to monitor the number of hours of eyeglass wear.

We might have found adaptive changes in the cross-links between accommodation and convergence if our subjects had used the reading spectacles continuously for longer durations. Nevertheless, our results suggest that there is no long-term impact of wearing the reading spectacles intermittently for a short-term on the accommodation and vergence cross-links; this was true for both subject groups.

Conclusions The results demonstrate that static accommodative response can be adapted in response to short-term treatment with reading spectacles.

The unique feature of this work is the finding of age invariance of this effect. Our results showed that the near and far points of accommodation recede after reading spectacles are worn and do not recover after 2 months of discontinued treatment. Nature of this test is such that the factor of fusional convergence also does not come into the picture.

The procedure was carried out at a distance of 33 cm with the help of Maddox wing and at a distance of 1 metre with the help of Maddox rod.

For each distance the first reading in prism dioptres was taken without any interposition of lenses and subsequent readings were taken after the interposition of - 1.

With the help of Synoptophore. The patient was asked to wear his correcting glasses if any. Slide for measuring angle kappa was placed before one eye. A black vertical line was presented to the other eye. The patient was asked to bisect the zero by the black vertical line.

### Eye exercises for best vision

Subjective angle was then noted in prism dioptres. The test was then repeated with the introduction of concave spherical lenses, - 1. Though the amount of proximal convergence is not completely eliminated in this method, the error introduced is negligible. Fifty male and fifty female patients of various age groups ranging from six to sixty one years [Table - 1][Table - 2] having normal visual acuity without or with correcting glasses were selected from eye O.

These patients had no ocular symptoms and reported to the eye O. Observation On analysing the values statistically the ratio was found to be the same for the same individual at different viewing distances i. Persons with decreased accommodative power due to presbyopia also showed this linear relationship.

The mean value was 2.

## Accommodation-convergence relationships and age.

Out of cases, in eleven the ratio was below 1. Only 12 cases had the range between 3. It is evident from [Table - 1][Table - 2] that the ratio does not differ much in the two sexes, the mean values being 2. On statistical analysis of the data there was hardly any change of the values found in individual cases. Subjective methods as described are simpler and quite accurate for clinical purposes. The ratio is generally believed to be inborn and thought to remain constant throughout life.

Because of this hereditary background the ratio has also been found to be variable from country to country. TAIT [10] found the highest and lowest ratios to be 5.