With accommodation at rest, total refractory power of crystalline lens is –
**Core Concept:**
The question is related to the accommodation process in the human eye, which is the ability of the crystalline lens to change its shape and focal length to bring distant objects into clear focus on the retina. This process is essential for maintaining near and far visual acuity. The accommodation process is powered by the ciliary body, a part of the uveal tract, which controls the zonules of Zinn and the ciliary muscle. The total refractive power of the crystalline lens at rest is the measure of how much the lens can change its refractive power during accommodation.
**Why the Correct Answer is Right:**
The correct answer is **D**. In the resting state, the refractive power of the crystalline lens is approximately -10 diopters. This value indicates that the lens can reduce its refractive power by approximately 10 diopters when the eye accommodates. The negative sign denotes the ability to reduce the refractive power, which is essential for focusing distant objects that require myopia (nearsightedness).
**Why Each Wrong Option is Incorrect:**
A) Option A is incorrect because it states that the resting refractive power is 0 diopters. In reality, the lens can reduce its refractive power, not increase it.
B) Option B is incorrect as it suggests a positive value for the resting refractive power, which contradicts the concept of reducing refractive power during accommodation.
C) Option C is incorrect because it provides a value of approximately -4 diopters, which is too low compared to the actual resting refractive power of the lens.
**Clinical Pearl:**
Understanding the resting refractive power of the crystalline lens is crucial for understanding the accommodation process in the eye and its role in maintaining clear vision. This concept is essential for medical students and physicians dealing with refractive errors and prescribing corrective lenses like glasses or contact lenses. The resting refractive power of the lens helps to explain how the eye adjusts its focus to maintain a clear image on the retina, particularly in cases of presbyopia, where the eye's ability to accommodate decreases with age.
**Correct Answer Explanation:**
The resting refractive power of the lens is important for students studying ophthalmology or optometry, as well as physicians dealing with refractive errors and prescribing corrective lenses. Understanding the lens' ability to reduce its refractive power contributes to understanding how the eye adjusts its focus to create a clear image on the retina, especially in cases of presbyopia, where the eye's ability to accommodate decreases with age.