Certified Ophthalmic Medical Technologist (COMT) Practice Exam

In the context of a prescription of +1.00 +1.00 x 90, how long is the Conoid of Sturm?

1. 25 cm long

2. 50 cm long

3. 75 cm long

4. 100 cm long

The correct answer is: 50 cm long

To understand the length of the Conoid of Sturm in relation to the prescription provided (+1.00 +1.00 x 90), it's important to recognize what the Conoid of Sturm represents. The Conoid of Sturm is related to astigmatism and depicts the distribution of light rays when viewed through a cylindrical lens, particularly in the context of a refractive error where two principal meridians are affected differently. In this prescription, there are two principal meridians with equal powers of +1.00 diopters. The specific axis of 90 degrees indicates that the meridians are oriented horizontally and vertically (or in relation to the axis). The relationship between the cylinder power and the distance to the focus (where the image is sharply defined) allows us to determine the length of the Conoid of Sturm. In this case, the formula to find the length of the Conoid of Sturm is given by a specific distance derived from the cylindrical power. For a cylinder of +1.00D, at an equivalent distance, the length is calculated as 100 cm divided by the cylinder power. Thus, in this instance: Length of the Conoid of Sturm = 100 cm / (1D) = 100 cm.