The minimum quantity of light required to elicit the accommodation reflex in man

If an emmetrope views a near object the visual axes of the eyes converge and the refractive power of the crystalline lenses increases, resulting in sharp vision without diplopia. While there is close harmony between the degree of convergence and the extent of accommodation, accurate accommodation can occur in the absence of convergence. Normally the conscious awareness of the distance of an object also assists in the production of the correct degree of accommodation. But accommodation can be elicited even without knowledge of the distance of the object from the eye, by suddenly placing a negative spherical lens of moderate power before the eye. The adjustment to this change in vergence of the light occurs rapidly without conscious effort on the part of the subject. It may justifiably be classed as a reflex. The purpose of this paper is to determine the minimum amount of light required to elicit the accommodation reflex. Some observations on the behaviour of the accommodation mechanism in darkness are also reported.