True statement about Jackson’s Cross – Cylinder test is
**Core Concept**
The Jackson's Cross-Cylinder test is a method used in ophthalmology to assess the refractive error of the eye, particularly to detect and measure astigmatism. It involves the use of a cross-cylinder lens, which has a cylindrical power with opposite axes, to determine the orientation and amount of astigmatism present in the eye.
**Why the Correct Answer is Right**
The Jackson's Cross-Cylinder test is a refinement of the previous methods of astigmatism detection, such as the Maddox Rod test. In this test, the cross-cylinder lens is placed in front of the patient's eye, and the patient is asked to look at a distant target. The lens is rotated in different axes, and the patient is asked to report when the astigmatism is at a maximum or minimum. This allows the examiner to determine the orientation and amount of astigmatism present in the eye, which is essential for prescribing corrective lenses. The test takes into account the cylinder axis and power to provide an accurate measurement of astigmatism.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Jackson's Cross-Cylinder test is specifically designed to measure astigmatism, not other types of refractive errors such as myopia or hyperopia.
**Option B:** This option is incorrect because the Jackson's Cross-Cylinder test does not involve the use of a Maddox Rod, which is a different tool used to detect astigmatism.
**Option C:** This option is incorrect because the Jackson's Cross-Cylinder test is a subjective test, meaning that it relies on the patient's perception of the astigmatism, rather than an objective measurement.
**Clinical Pearl / High-Yield Fact**
A key point to remember when performing the Jackson's Cross-Cylinder test is to always start with the cross-cylinder lens at a power of 0.50 diopters and then adjust the power and axis accordingly. This helps to ensure accurate measurement of astigmatism and prevents over- or under-correction.
**Correct Answer: C. This is a subjective test.**