The DeZeng Refractometer, manufactured by the Cataract Optical Co. of Buffalo, NY and marked on the barrel with the names of DeZeng’s Refractometer, Spencer Lens Co. Buffalo, Bausch & Lomb Optical Co. Rochester NY & New York City as Makers, was patented by Henry DeZeng Jr. of Geneva, NY on December 3, 1895. This instrument represents one of the most important early attempts to create a self-contained objective refraction device — a single instrument capable of measuring a patient’s refractive error without the laborious process of individually inserting trial lenses into a trial frame.
The instrument works by having the patient view an object through the eyepiece while the examiner rotates the dials until the object appears most clear. The main viewing barrel is approximately 9 inches long with an extended height on the adjustable cast iron or metal tripod of approximately 20 inches. Behind the eyepiece is a rotating wheel of lenses of various powers, with a graduated dial on the side with adjustments for myopia and hyperopia. Two wheels of lenses, each with 7 openings, are mounted at the eye end — each wheel marked “concave cylinders.” The two wheels together can be rotated on the optical axis by means of a geared drive, with the peripheral degree scale marked “axis register.” Inside the 9-inch outer cylinder is a lens barrel which can be ratcheted in and out. The scale on top is marked from 0-9 with portions inscribed “myopia, concave, and spherical,” while behind the focusing knob is a 3-inch diameter circular scale marked “hypermetropia convex spherical” divided from 0-18, and “myopia concave spherical” divided from 0-15.
The fundamental challenge this instrument faced — and the reason very few were ever offered — was the natural ability of the eye to focus through accommodation, which could throw off the refraction result. This limitation meant the instrument never replaced the trial lens set and retinoscope in clinical practice. Nevertheless the DeZeng Refractometer is considered a highly prized collectible for those interested in the history of optometry and ophthalmology, and its nickel-plated brass construction with cast iron tripod finished in black enamel makes it one of the most visually impressive instruments in any ophthalmic collection.
