The Old Eye

How Vision Works


The eye contains receptors for vision. Perception of an object is achieved when light reflected from the object enters the eye through the pupil and is focused by the cornea and lens to form sharp images of the object on the retina. The retina is the network of neurons that contains the receptors for vision.


The neuron contains dendrites, cell body, and the axon. Information from the stimulus is turned into an electrical signal, via transduction. That electrical activity moves down the neuron in the form of an action potential. When it arrives at the end of the axon, the information crosses the synapse by communication with neurotransmitters. The neurotransmitters bind to specific receptors of neurons to get the information to the visual receiving area (striate cortex).

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What is Presbyopia?

Presbyopia is a condition involving the loss of the eye's ability to focus on close objects. It occurs as part of the normal aging process, with symptoms beginning to appear around the age of 40 to 45 years old.

When viewing an object, the eye needs to focus. This is done by tiny ciliary muscles that pull and push the lens, adjusting its curvature. This adjust the eye's ability to bring objects into focus.

As an individual ages, the lens becomes less flexible and elastic, and the muscles become less powerful. The changes result in inadequate adjustment of the lens, which makes objects that are close will appear blurry.

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There is no cure for presbyopia. In order to compensate for a decrease in vision, a physician can prescribe reading, bifocal, or trifocal eyeglasses.

An alternative option of treatment is laser-assisted in-situ keratomileusis (LASIK). While this helps restore a minor amount of the vision lost, there is a side-effect to the surgery. The surgery can cause a reduction in binocular distance vision and depth perception.


Nothing can be done to prevent presbyopia. It is normal with aging. An individual's vision will continue to change until around age 65, in which changes to vision usually stop.



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Goldstein, B. E. (2014). Sensation and Perception. Belmont: Wadsworth Cengage Learning.

Neuron Structure. (n.d.). Retrieved from

Presbyopia. (n.d.). Retrieved from Pearl Optics:

Presbyopia. (2013). Retrieved from Health and Wellness Resource Center: