Using the formula OZ + 2(ICW) + 2(PCW) = OAD, if OAD = 9.2 mm, ICW = 0.3 mm, and PCW = 0.4 mm, what is OZ?

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Multiple Choice

Using the formula OZ + 2(ICW) + 2(PCW) = OAD, if OAD = 9.2 mm, ICW = 0.3 mm, and PCW = 0.4 mm, what is OZ?

Explanation:
The question tests how the optic zone diameter fits into the overall lens diameter when you account for the inner and peripheral curve widths. In a gas permeable lens, the overall diameter is made up of the optic zone plus two inner curve widths and two peripheral curve widths: OAD = OZ + 2(ICW) + 2(PCW). To isolate the optic zone, subtract the contributions of the curves from the overall diameter. Compute the curve contributions: 2(ICW) = 2 × 0.3 = 0.6 mm, and 2(PCW) = 2 × 0.4 = 0.8 mm. Their sum is 1.4 mm. Then OZ = OAD − 1.4 = 9.2 − 1.4 = 7.8 mm. Therefore, the optic zone diameter is 7.8 mm.

The question tests how the optic zone diameter fits into the overall lens diameter when you account for the inner and peripheral curve widths. In a gas permeable lens, the overall diameter is made up of the optic zone plus two inner curve widths and two peripheral curve widths: OAD = OZ + 2(ICW) + 2(PCW). To isolate the optic zone, subtract the contributions of the curves from the overall diameter.

Compute the curve contributions: 2(ICW) = 2 × 0.3 = 0.6 mm, and 2(PCW) = 2 × 0.4 = 0.8 mm. Their sum is 1.4 mm. Then OZ = OAD − 1.4 = 9.2 − 1.4 = 7.8 mm.

Therefore, the optic zone diameter is 7.8 mm.

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