For a normal eye, the cornea of eye provides a converging power of `40 D` and the least converging power of the eye lens behind the cornea is `20 D`. Using this information, the distance between the retina and the cornea eye lens can be estimated to be

Options

A. `5 cm`
B. `2.5cm`
C. `1.67 cm`
D. `1.5 cm`

Answer

To find the distance between the retina and the cornea eye lens, we can follow these steps:

### Step 1: Understand the Given Information
- The converging power of the cornea (P1) = 40 D (diopters)
- The least converging power of the eye lens (P2) = 20 D (diopters)

### Step 2: Calculate the Total Power of the Eye
The total power (P) of the eye is the sum of the powers of the cornea and the eye lens:
\[ P = P1 + P2 \]
Substituting the values:
\[ P = 40 \, D + 20 \, D = 60 \, D \]

### Step 3: Calculate the Focal Length of the Eye
The focal length (F) can be calculated using the formula:
\[ F = \frac{1}{P} \]
Substituting the total power:
\[ F = \frac{1}{60 \, D} \]
Since 1 D = 1 m⁻¹, we convert this to centimeters:
\[ F = \frac{100}{60} \, cm = \frac{10}{6} \, cm = \frac{5}{3} \, cm \]

### Step 4: Final Result
The focal length of the eye, which represents the distance between the cornea eye lens and the retina, is:
\[ F \approx 1.67 \, cm \]

Thus, the distance between the retina and the cornea eye lens is approximately **1.67 cm**.

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