If the identification mark on a toric lens rotates 5 degrees to the observer's left and the glasses prescription is -2.50 + 2.00 X100, what contact lens prescription should be ordered?

If the identification mark on a toric lens rotates 5 degrees to the observer's left and the glasses prescription is -2.50 + 2.00 X100, what contact lens prescription should be ordered?

• A. -2.50 + 2.00 X100
• B. -1.50 + 2.00 X105
• C. -2.50 + 3.00 X105
• D. -2.50 + 2.00 X105

Answer: (D)

Toric contact lenses must sit with their cylinder axis aligned to the eye. If the lens rotates on the eye, the axis of correction shifts away from the planned orientation, reducing the effectiveness of the cylindrical correction. Here, the identification mark rotates 5 degrees to the observer’s left, which means the lens is rotated 5 degrees counterclockwise from its intended axis. To restore the axis to match the glasses prescription, you compensate by increasing the axis angle by the same amount in the clockwise direction. The glasses Rx has an axis of 100 degrees, so the contact lens axis should be adjusted to 105 degrees. The sphere and cylinder values stay the same, since rotation affects only the axis, not the power magnitudes. Therefore, the correct contact lens prescription is -2.50 sphere with +2.00 cylinder at 105 degrees.

Toric contact lenses must sit with their cylinder axis aligned to the eye. If the lens rotates on the eye, the axis of correction shifts away from the planned orientation, reducing the effectiveness of the cylindrical correction. Here, the identification mark rotates 5 degrees to the observer’s left, which means the lens is rotated 5 degrees counterclockwise from its intended axis.

To restore the axis to match the glasses prescription, you compensate by increasing the axis angle by the same amount in the clockwise direction. The glasses Rx has an axis of 100 degrees, so the contact lens axis should be adjusted to 105 degrees. The sphere and cylinder values stay the same, since rotation affects only the axis, not the power magnitudes.

Therefore, the correct contact lens prescription is -2.50 sphere with +2.00 cylinder at 105 degrees.