Certified Ophthalmic Assistant Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

The notation -2.50 +1.00 X175 describes a lens prescription using minus cylinder format. In this format, the first number indicates the spherical component of the lens prescription, the second number represents the cylinder component, and the angle provides the orientation of the cylinder.

To convert -2.50 +1.00 X175 to the plus cylinder format, which is a common requirement for interpreting such prescriptions, a few steps need to be followed. The first step involves understanding that you need to change the angle by 90 degrees, which transforms the cylinder axis from 175 degrees to 85 degrees (175 - 90 = 85).

Next, you adjust the sphere and cylinder accordingly. When moving from minus cylinder to plus cylinder, you increase the spherical value and decrease the cylindrical value. Therefore, -2.50 is increased by the value of the cylinder (+1.00), resulting in a new spherical value of -2.50 + 1.00 = -1.50. The cylinder component, being switched over from plus to minus, becomes -1.00.

This gives the new notation of -1.50 -1.00 X85. The corresponding answer in the options reflects this conversion correctly.

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