Changes in corneal curvature during accommodation in chicks.

Evidence is presented for an active corneal component of accommodation in chicks. Using anesthetized chicks, consistent increases in corneal curvature were observed during accommodation produced either by electrical stimulation of the Edinger-Westphal nucleus or by topical application of 0.4% nicotine sulfate to the cornea. Electrical stimulation produced a mean accommodative amplitude of 9.2 diopters (D) and a change in corneal power of 3.9 D whereas nicotine treatment elicited 15.1 D of accommodation and 6.1 D of change in corneal power. The change in corneal power increased proportionately with accommodative amplitude up to about 10 D of total accommodation where the corneal power change appeared to level off at approximately 6 D. This limit to corneal curvature change implies that it plays a proportionately greater role in the lower range of accommodation.