In 1956, aspheric ophthalmic lenses for subnormal vision were developed by Dr. David Volk. He found that an aspheric surface corrected the aberrations present in more common spherical lenses.
Several developments occurred through the years, leading up to 1982 when all Volk lenses for indirect ophthalmoscopy were redesigned with both surfaces aspheric, providing a substantial improvement in image quality.
A series of indirect ophthalmoscopy lenses was developed, resulting in the choice of the 90 Diopter lens as the most practical for indirect ophthalmoscopy with the slit lamp. The Volk 60D and 90D lenses were commercialized providing a variety of characteristics; magnification, field of view and undilated pupil examination.
The 60D and 90D lenses have been known as the industry standard for decades, having revolutionized the slit lamp examination in the 1970s.