Retinal vascular micrometry by the use of a measuring ophthalmoscope.

THE eye is the only part of the body in which blood vessels can readily be observed. In disease, retinal blood vessels may show pathological variations in calibre, the severity of which at times reflects the progress of the disease, whether local as in retinitis pigmentosa, or systemic as in spastic hypertension. Spasticity of retinal vessels may show measurable alteration after treatment, in particular during the exhibition of vasodilator drugs. It was felt that a portable instrument sufficiently accurate to measure variations in the calibre of retinal vessels would be of clinical value. Attempts have previously been made to obtain absolute measurements of delineable, ophthalmoscopically visible retinal structures in the fundus. Numerous methods have been described since Zander (1864) first used a graticule with indirect ophthalmoscopy to measure the calibre of retinal arterioles. Lo Cascio (1922) used a graticule on the heliometer principle, and Lobeck (1934), working independently, produced a more effective heliometer method using the Gullstrand ophthalmoscope. The graticule described by Morgan (1927), which was used by many research workers, was modified by Neame (1936). A further modification, using a prism displacement method, was introduced by Cusick, Benson, and Boothby (1940). Angioscotometry (Solanes, 1947) and modem fundus photography (Lambert, 1934) are two other methods of vascular micrometry. Some of these methods involve the use of complicated apparatus and others are insufficiently accurate to measure the calibre of the smaller retinal blood vessels. For routine hospital work, it was felt that some adaptation of Morgan's graticule used in conjunction with Keeler's electric measuring ophthalmoscope would prove a practical method.