Case Report: Adaptation of a Telescope with a Minus Lens Cap for Highly Myopic Patient

This case report demonstrates a novel approach of using the optical principle of vergence amplification to correct for a visually impaired patient's ametropia while using a telescope system. This approach is easy to apply clinically.

The purpose of this study was to present a novel approach of correcting high myopia for a patient with visual impairment using a spectacle-mounted telescope.

A 51-year-old man desired improved distance vision for television viewing and facial recognition. His refractive error was -18.00 diopter sphere in each eye with best-corrected acuities of 5/225 (20/900 Snellen equivalent) for the right eye and 10/225 (20/450) for the left eye. Over the years, multiple attempts at contact lens use were unsuccessful, and the patient used spectacle prescription. After evaluating telescope systems, the patient was successful with a 7 × 30 Beecher Mirage Keplerian telescope system. This system cannot be worn over glasses. To correct his ametropia, a -0.25-diopter minus lens cap was applied in front of the objective lens of the telescope, capitalizing on the property of vergence amplification. In addition, the tube length was adjusted. Adding lenses in front of the telescope and focusing the telescope can both affect the angular magnification of the system. Depending on the lenses used, type of telescope, and refractive error, there can be an increase or decrease in angular magnification. In this case, the minus lens at the front of the telescope decreased the power of the objective lens, and the focusing for the remaining uncorrected myopia increased the power of the ocular lens. Both of these factors contributed to increased resultant angular magnification for this patient. The patient achieved 10/30 (20/60) vision and reported success with his distance vision.

Minus-powered lens caps over the objective lens are a viable option for highly myopic individuals who wish to use premanufactured spectacle-mounted telescopes.