Question

Describe the sequence of changes that occur during accommodation. Why is it more of a strain on the eyes to look at a small nearby object than at large objects far away?

Short answer

Accommodation in the eye involves the convergence of the eyes, constriction of the pupil, increase in lens curvature, and increase in the lens refractive index to focus on objects at different distances. Focusing on small nearby objects causes more eye strain than large objects far away due to the greater amount of lens curvature, convergence, and pupil constriction needed, as well as the increased effort to maintain clear vision with a reduced depth of focus.

Step-by-step solution

Understand Accommodation

Accommodation is the process by which the eye adjusts its focus to see objects at varying distances. The eye changes its optical power by altering the shape of its lens to bring images of objects at different distances into focus on the retina.

Describe the Sequence of Changes During Accommodation

The accommodation process consists of several steps: 1. Convergence of the eyes: When focusing on a near object, the eyes rotate towards each other so that both can focus on the target. 2. Constriction of the pupil: The diameter of the pupil decreases to help improve the depth of focus and reduce the amount of spherical aberrations. 3. Increase in the lens curvature: The ciliary muscles encircling the lens contract, decreasing the tension in the suspensory ligaments, and allowing the lens to become more rounded and increase its focusing power. 4. Increase in the refractive index of the lens: As the lens curvature increases, so does the refractive index of the lens, further increasing the eye's focusing power.

Explain How Nearby Objects Cause More Strain on the Eyes

Looking at small nearby objects requires a higher degree of accommodation than looking at large objects far away. This can result in increased eye strain due to the following reasons: 1. More lens curvature is needed to focus on near objects, causing the ciliary muscles to contract more and exert more force on the lens. 2. Greater convergence of the eyes is required, which involves more effort from the eye muscles to maintain this position. 3. A smaller pupil diameter may be needed to maintain proper focus, particularly when reading small print or texts, which can also contribute to eye strain. 4. The higher degree of accommodation can lead to a reduced depth of focus, causing the eye to work harder to maintain clear vision. In summary, accommodation is the process where the eye adapts to view objects at various distances by adjusting the shape of its lens. Looking at small nearby objects generates more strain on the eyes than looking at large objects far away due to the increased lens curvature, convergence of the eyes, and required constriction of the pupil.