The eye uses two main surfaces of focus on anything. The first is the outer layer of the eye known as the cornea, and the second being the lens which is a concave structure suspended mid-way through the eye. It is the lens that changes shape to help you focus on objects at different distances, your cornea generally stays the same shape throughout life.
The ability of the lens to focus near objects is known as accommodation.
When looking at distant objects, your accommodation is fully relaxed if you have a perfect distance prescription or if you are wearing distance spectacles. When wanting to focus on near objects your eyes have an involuntary response and three things happen. Your pupils constrict, your eyes converge together and your accommodation muscles contact to change the shape of the lens.
With this contraction of the muscles, the lens becomes slightly thicker which then helps your eyes to focus a clear image on to the retina- the seeing part of the eye.
As we get older, unfortunately our ability to accommodate reduces. For most people, this will start to manifest itself in their early 40’s, certain ethnic groups have accommodation problems in the 30’s, such as afro-Caribbean, and there are certain eye disease and developmental abnormalities which affect our ability to accommodate.
We will focus on the age-related presbyopia for now.
So, as we get to our 40’s, we notice it becomes increasingly difficult to focus as well on near objects as we did when we were younger. We may notice we hold our books or hand-held devices further away to be able to focus on them or we may need more light than previous to be able to see.