Accommodative fluctuations in Adie's syndrome

Adie syndrome: evidence for refractive error and accomodative asymmetry as the cause of amblyopia

PURPOSE

To report objective changes in accommodation in a child with Adie syndrome.

METHODS

A child aged 2 years 10 months when initially examined was found to have good visual acuity in both eyes, a low degree of hypermetropia (isometropic), and Adie pupil presumed to be caused by chicken pox that had occurred 2 months earlier. Amblyopia developed but responded well to treatment, which involved correction of the refractive error and occlusion therapy. Objective changes in the refraction of the eye were measured on the Canon R1 autorefractor at 3.8 m and 33 cm.

RESULT

The degree of accommodation in the affected eye when both eyes were open was markedly reduced.

CONCLUSION

The presence of isometropic hypermetropia, which remains uncorrected when Adie syndrome is present, can lead to the development of amblyopia in a child.

In vivo determination of the biomechanical properties of the component elements of the accommodation mechanism

A method of obtaining in vivo information about the component elements of the accommodation mechanism is described. Changes in axial lens thickness during accommodation are measured continuously by ultrasonographic biometry. The measurements are fitted with a dynamic biomechanical model of the mechanism of accommodation. This gives a time constant that depends both on the direction of accommodation and on the properties of the lens, zonules and choroid. Two ratios can be calculated that give information about the visco-elastic properties of the lens, zonules and choroid. This information is especially useful to evaluate the changes that lead to presbyopia.

Mean response and oscillations of accommodation with colour and contrast

The mean level and microfluctuations of accommodation were objectively recorded, in natural viewing conditions, by infrared optometry on steady presentation of various combinations of achromatic and coloured Snellen E on achromatic or coloured fields, with or without a luminance contrast. In addition to the absolute mean power spectrum of the microfluctuations, the HF/LF ratio of the high (HF, 0.5-6 Hz) and low (LF, 0-0.5 Hz) frequency activity of this phenomenon, which provides a sensitive objective description of the control, was analysed. In the case of maximum luminance contrast, for any monochrome situation, the HF/LF ratio decreases when changing from an achromatic-only contrast to a saturated coloured situation. At the same time, the relative shifts of the mean level of accommodation, which compensate ocular chromatism under coloured conditions, increase with colour saturation. In the case of an isoluminant chromatic contrast, the decrease in the HF/LF ratio was significant. This result confirms the inefficiency of chromatic contrast to control accommodation. Furthermore, this study confirms that both LF and HF absolute activity of the microfluctuations of accommodation are usually related to the stimulus characteristics. Their antagonistic behaviour is an argument for considering the HF/LF ratio.

Accommodative adaptation and age of onset of myopia

Tonic accommodation in an empty field and accommodative adaptation, defined as accommodation shift after 2 min viewing of a 4 D near task, were measured using an infrared optometer. Subjects were classified into three types: emmetropes (n = 18), early onset myopes (n = 18) and late onset myopes (n = 15). The relationship between accommodative adaptation and the onset age of myopia were compared. There was no statistical difference in the pre-task tonic accommodation among the three subject groups. However, the accommodative adaptation differed in the three groups during the 5 min post-task period. The average accommodative adaptation of emmetropia, early onset myopia and late onset myopia were 0.66, 0.27 and 1.19 D, respectively. Accommodative adaptation in the late onset myopia group was significantly higher than in the emmetropia group. Furthermore, the accommodative adaptation in the early onset myopia group was significantly lower than in the emmetropia group. Two possible aetiologies of myopia are discussed: one for the group which shows low accommodative adaptation that has no relationship with the age of onset and another for the group which shows high accommodative adaptation that has a relationship to an onset age of 15 years or later. The aetiology is also considered with regard to a potentiating chemical effect on the synapses of the ciliary muscle.