they also converge their eyes and, as a result, constrict their pupils. However, the constriction of the pupils is not part of the process called lens accommodation. The combination of these three movements (accommodation, convergence and miosis) is under the control of the Edinger-Westphal nucleus and is referred to as the near triad, or accommodation reflex. While it is well understood that proper convergence is necessary to prevent diplopia, the functional role of the pupillary constriction remains less clear. Arguably, it may increase the depth of field by reducing the aperture of the eye, and thus reduce the amount of accommodation needed to bring the image in focus on the retina. There is a measurable ratio (Matthiessen's ratio) between how much convergence takes place because of accommodation (AC/A ratio, CA/C ratio). Abnormalities with this can lead to binocular vision problems. Anomalies of accommodation There are many types of accommodation anomalies. It can be broadly classified into two, decreased accommodation and increased accommodation. Decreased accommodation may occur due to physiological (presbyopia), pharmacological (cycloplegia) or pathological. Excessive accommodation and spasm of accommodation are types of increased accommodation. Presbyopia Presbyopia, physiological insufficiency of accommodation due to age related changes in lens (decreased elasticity and increased hardness) and ciliary muscle power is the commonest form of accommodative dysfunction. It will cause gradual decrease in near vision. Accommodative insufficiency Accommodative insufficiency is the condition where amplitude of accommodation of a person is lesser compared to physiological limits for their age. Premature sclerosis of lens or ciliary muscle weaknesses due to systemic or local cases may cause accommodative insufficiency. Accommodative insufficiency is further categorised into different categories. Ill-sustained accommodation Ill-sustained accommodation is a condition similar to accommodative insufficiency. In this, range of accommodation will be normal, but after excessive near work accommodative power will decrease. Paralysis of accommodation In paralysis of accommodation, amplitude of accommodation is either markedly reduced or completely absent (cycloplegia). It may occur due to ciliary muscle paralysis or occulomotor nerve paralysis. Parasympatholytic drugs like atropine will also cause paralysis of accommodation. Unequal accommodation If there is amplitude of accommodation between the eyes differ 0.5 dioptre or more, it is considered as unequal. Organic diseases, head trauma or functional amblyopia may be responsible for unequal accommodation. Accommodative infacility Accommodative infacility is also known as accommodative inertia. In this condition there will be difficulty in changing accommodation from one point to other. There may