A patient reports that her eyes feel strange when reading 6mm below the optical centers of her new glasses. How much vertical prism is induced when she reads?

When considering how much vertical prism is induced when a patient reads 6 mm below the optical centers of their glasses, we can use the concept of prism diopters, which are calculated based on the displacement of light through a given distance.

Prism diopters are calculated using the formula:

Prism Diopters = (deviation in centimeters) / (distance in meters).

For a deviation of 6 mm, we convert this to centimeters, which gives us 0.6 cm. The reading distance for typical scenarios is often taken as 40 cm (or 0.4 m) for near tasks like reading. Plugging these values into our formula gives:

Prism Diopters = 0.6 cm / 0.4 m = 1.5 prism diopters.

However, we need to account for the specifics in this situation. The formula showing 2 mm deviation typically corresponds to 1 prism diopter.

If we dive deeper into the height deviation observed due to the position of the optical center being misaligned by 6 mm when the patient is reading, we find there’s a further adjustment calculating the inherent strength of the lens power into consideration of the focal points (if we consider that the eyes are slightly converged