Accommodative convergence is that portion of the range of

inward rotation Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relat ...

of both

eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...

s (i.e.

convergence Convergence may refer to: Arts and media Literature *''Convergence'' (book series), edited by Ruth Nanda Anshen * "Convergence" (comics), two separate story lines published by DC Comics: **A four-part crossover storyline that united the four Weir ...

) that occurs in response to an increase in

optical power In optics, optical power (also referred to as dioptric power, refractive power, focusing power, or convergence power) is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the reciprocal of th ...

for focusing by the

crystalline lens The lens, or crystalline lens, is a transparent biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. By changing shape, it functions to change the focal length of the eye so that it ca ...

(i.e. accommodation).Cassin, B. and Solomon, S. ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Company, 1990. When the human eye engages the accommodation system to focus on a near object, signal is automatically sent to the

extraocular muscles The extraocular muscles (extrinsic ocular muscles), are the seven extrinsic muscles of the human eye. Six of the extraocular muscles, the four recti muscles, and the superior and inferior oblique muscles, control movement of the eye and the ot ...

that are responsible for turning their eyes inward. This is helpful for maintaining single, clear, and comfortable vision during reading or similar near tasks. However, errors in this relationship can cause problems, such as

hyperopic Far-sightedness, also known as long-sightedness, hypermetropia, or hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blurred effect is due to incoming light being focused behind, in ...

individuals having a tendency for crossed eyes because of the over exertion of their accommodation system. Clinically, accommodative convergence is measured as a ratio of convergence, measured in prism diopters, to accommodation, measured in diopters of near demand. The patient is instructed to make a near target perfectly clear and their phoria is measured as the focusing demand on the eye is changed with lenses. To determine stimulus AC/A, the denominator refers to the value of the stimulus, whereas to determine response AC/A, the actual accommodation elicited is the denominator. Determination of response AC/A an increase in AC/A mainly after 40 years of age, whereas assessment of the stimulus AC/A does not show change in AC/A with increasing age. Whether there is a significant increase in the response AC/A before age 40 is unclear. Research on convergence accommodation (CA) shows a decrease in CA/C, whether measured by response or stimulus methods, with increasing age. Schor C, Narayan V. Graphical analysis of prism adaptation, convergence accommodation, and accommodative convergence. Am J Optom Physiol Optics. 1982;59:774-784. 10. Wick B, Currie D. Convergence accommodation: Laborator)' and clinical evaluation. Optom Vis Sci. 1991;68:226-231.

References

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See also

References