Prescription of simple myopic astigmatism:
**Core Concept**
Simple myopic astigmatism is a type of refractive error characterized by unequal refractive powers in two meridians of the cornea or lens, resulting in blurred vision at all distances. This condition can be corrected with cylindrical lenses that compensate for the irregular curvature of the cornea or lens.
**Why the Correct Answer is Right**
The prescription of simple myopic astigmatism involves correcting the refractive error with a cylindrical lens. The cylindrical lens has a different refractive power in one meridian than in the other, which compensates for the irregular curvature of the cornea or lens. The power of the cylindrical lens is measured in diopters (D) and is expressed as a minus value (-) followed by the power, e.g., -2.00 x 90. This indicates that the lens has a power of -2.00 D in the 90-degree meridian.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is likely incorrect because it does not specify the meridian in which the cylindrical power is applied. In astigmatism, the cylindrical power must be applied in the meridian where the refractive error is greatest.
* **Option B:** This option is likely incorrect because it does not specify the correct orientation of the cylindrical power. In astigmatism, the cylindrical power is typically oriented at the axis of the meridian where the refractive error is greatest.
* **Option C:** This option is likely incorrect because it does not specify the correct power of the cylindrical lens. In astigmatism, the power of the cylindrical lens is typically measured in diopters (D) and is expressed as a minus value (-) followed by the power.
**Clinical Pearl / High-Yield Fact**
When prescribing cylindrical lenses for astigmatism, it's essential to specify the correct meridian and power of the cylindrical lens to ensure accurate correction of the refractive error. A common mistake is to prescribe the cylindrical lens in the wrong meridian or with an incorrect power, which can lead to suboptimal vision and patient dissatisfaction.
**Correct Answer:** D. -2.00 x 90