Anatomy & Physiology
Accommodation & Convergence

Tunics
Fibrous Tunic:	Outer protective coat of the eye. Consists of the Sclera and Cornea.
Vascular Tunic:	Also known as the uveal tract. Consists of three parts: The iris, ciliary body and the choroid.
Neural Tunic:	Consists of the retina.

Certain structures of the eye may be grouped together to form what are called tunics or coverings. These are outlined in the above table.

 

Accommodation

1) The ciliary muscle relaxes allowing for a thickening of the crystalline lens.

2) The eyes converge

3) The pupils constrict.

During accommodation, the eye adjusts for viewing objects at various distances. This is accomplished by the crystalline lens changing shape through the action of the ciliary muscle. Associated with accomodation is convergence and the constricting of the pupils.

 

Distance PD	Subtact for Near
Less than 62 mm	2 mm
62 - 66 mm	3 mm
More than 66 mm	4 mm

Since the eyes converge when viewing an object at a near distance as when reading, the pupillary distance for near vision is narrower than that for distance viewing. The amount the eyes will converge for near will vary from one individual to another and for complete accuracy both the distance and near PD should be physically measured. However, as a general rule-of-thumb eyes with wider distance PD�s will converge more for reading than those with narrower distance PD�s.