**Question:** Shoening of 2 mm of axial length of eye ball causes -

**Core Concept:** Axial length is the distance from the corneal vertex to the vitreous-retinal junction, and it is an important factor in determining an individual's refractive error and the prescription of corrective lenses.

**Why the Correct Answer is Right:** Shoening refers to the process of removing the lens of the eye, usually performed in cataract surgery. In this context, the removal of the lens changes the optical properties of the eye and alters the refractive power, which in turn affects the visual acuity.

When the lens is removed, particularly if a significant amount such as 2 mm is removed, it leads to an increase in the overall axial length of the eye. This results in a decrease in the effective focal length of the eye, causing a decrease in the refractive power and subsequently reducing the ability to focus light onto the retina.

**Why Each Wrong Option is Incorrect:**

A. **Incorrect:** Shoening in any amount does not directly affect the axial length, as the lens is not a part of the axial length calculation. However, a decrease in lens thickness may indirectly influence the axial length by changing the refractive power.

B. **Incorrect:** Shoening does not cause a direct increase in the axial length of the eye. Instead, it affects the refractive power, leading to a decrease in visual acuity.

C. **Incorrect:** Shoening does not directly affect the cornea or sclera, as these structures are not part of the axial length calculation. The change in axial length is primarily due to the removal of the lens.

D. **Incorrect:** Shoening does not solely result in a decrease in the refractive power. While it does alter the refractive power, it also affects the overall axial length, contributing to the decrease in visual acuity.

**Clinical Pearl:** Understanding the relationship between axial length, refractive power, and visual acuity is crucial when planning and evaluating the outcomes of cataract surgery. By removing the lens, surgeons aim to correct refractive errors and improve visual acuity.

**Correct Answer:** C. Shoening causes a decrease in refractive power and visual acuity, which is ultimately due to the removal of the lens, which is a significant contributor to the overall refractive power of the eye.

In summary, shoening refers to the surgical removal of the lens in cataract surgery, and although it affects the refractive power, the primary mechanism by which shoening reduces visual acuity is by increasing the axial length of the eye due to the absence of the lens, which is a significant component of the eye's refractive power.