It may be constant, intermittent, unilateral or bilateral. It does so by contracting the ciliary muscle which releases the tension on the zonular fibres, allowing the elastic lens capsule to increase its curvature, especially that of the front surface. This is accomplished by dynamic retinoscopy, by autorefractors or by visually evoked cortical potentials. If the patient is a low hyperope or emmetrope, it will give rise to pseudomyopia false myopia, hypertonic myopia, spurious myopia. It can also occur as a result of a spasm of accommodation.
The ciliary muscle is controlled by the parasympathetic system, which is triggered by an out of focus retinal image. The amount by which the accommodative response of the eye is less than the dioptric stimulus to accommodation, as usually occurs when fixating an object at near. It can be negative using convex lenses until the image blurs.
It can be positive using concave lenses until the image blurs. Management includes removal of the primary cause, if possible e. This is presumably due to a balance between a parasympathetic innervation to the circular fibres of the ciliary muscle and a sympathetic innervation to the longitudinal fibres of the ciliary muscle. Part of the range of accommodation is virtual in the case of the hypermetrope.
Absence of an accommodative lag may indicate latent hyperopia. The condition occurring in dynamic retinoscopy in which the neutral point is situated further from the eyes than is the retinoscopic target.
It could be due to uncorrected hyperopia or indicate accommodative insufficiency. It may be initiated when the eye changes fixation from far to near, or it may be induced by convergence.
Thus, the resting state of accommodation would correspond to a position of equilibrium between the two systems. The term is sometimes used incorrectly to refer to the amplitude of accommodation without the influence of the depth of focus e. Diagnosis is facilitated by cycloplegic refraction to rule out latent hyperopia. In these conditions, the accommodative system of the eye tends to return to its position of rest or tonic accommodation. Along with these changes are an increase in the thickness of the lens, a decrease in its equatorial diameter and a reduction in pupil size.
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