We measure rays of light as they are reflected by the retina.
We measure rays of light as they are reflected by the retina.
Optometrists use retinoscopes as a form of objective refraction test. The instruments are used to illuminate the internal eye and to observe and measure the rays of light as they are reflected by the retina. In this way the optometrist can achieve an objective examination of the eye and the manner in which it functions as an organic optical instrument. In order to obtain an accurate refraction for the patient the optometrist may then need to perform various subjective tests in which the patient's opinion on the effect of selected lenses will be sought. Nevertheless retinoscopy has proved over the decades to be an excellent first start and an effective means of reducing the time spent on an examination without compromising the quality of the result. With very young patients or those who have difficulty communicating, retinosocopy has sometimes been the main method of obtaining a refraction. Today it remains a very useful instrument even following the advent of automated refraction techniques. Retinoscopy is also known as skiametry, a more accurate term that indicates that shadows (reflexes) are being observed. The retina itself is transparent and casts no shadows.
Sir William Bowman (1816-92) was the first to investigate the shadow effect that paved the way for retinoscopy. He observed an interesting shadow (in fact it was a linear fundus reflex) in 1859. He was using a Helmholtz ophthalmoscope at the time and thus the history of retinoscopes and ophthalmoscopes was intertwined from the start. Indeed another early phrase for retinoscopy was 'optometric ophthalmoscopy'. Bowman was able to describe a method of detecting, if not yet quantifying, levels of astigmatism in eyes with keratoconus (a misshapen cornea). Bowman considered his technique to be primarily a diagnostic one - to detect whether or not a cornea was cone-shaped - but he apparently discussed with Donders the theoretical value of using shadow phenomena to locate the principal meridians. Whatever, this was the world's first objective refraction technique.
In 1873 the French ophthalmologist Ferdinand Cuignet (b.1823) used a simple ophthalmoscope to compare the variable reflexes in eyes which subjective testing had already determined to be experiencing different refractive errors. This was a qualitative test. By observing the size, brightness, speed or direction of the reflex Cuignet could now classify the patient's error in simple categories such as myopia, hyperopia or astigmatism. Somewhat misleadingly he called his technique keratoscopie, thinking that the cornea was responsible for his obervations. Cuignet was a military surgeon. The civilian ophthalmologists, such as Edmond Landolt, looked down on him and did not give him the credit his (admittedly imperfect) discoveries deserved.
In 1878 Cuignet's pupil, M. Mengin, published an accurate explanation, thereby proving Landolt's suggestion that the source of the reflex was the fundus rather than the cornea.
Finally, in 1880, H. Parent (1849-1924) introduced the quantitative refraction test. It was now possible to measure the exact amount of refractive error using lenses. He also coined the term retinoscopie.
Other names that were suggested for the technique included:
Even though the technique was gradually being put to effective use, at the turn of the 19th and 20th centuries there was still considerable debate over how retinoscopy worked. The three principal theories to emerge were:
Of these, the first has enjoyed the longest favour and still informs our basic understanding of the technique today.
Early retinoscopes were just a perforated mirror on the end of a handle, but optometrists continued to be trained in their use into the modern era, so dating them accurately can be almost impossible. The three shown here are the 'Orthops' retinoscope, manufactured probably by either Raphaels Ltd or Culver in the early-mid 20th century, the 'Bright Reflex' retinoscope by J & R Fleming Ltd and a large mirror variety.
In 1903 the American practitioner Alexander Duane promoted the use of cylindrical lenses in retinoscopy.
This MacNab Retinoscope from 1909 is a rather more sophisticated affair with an ivory and gilt screw-on handle. It includes an axis indicator marked 0-180 operated by a geared wheel beneath the sight hole. It was designed by Angus MacNab (c.1876-1914), a Scotsman born in New Zealand, who eventually ended up in London.
In early retinoscopic examinations the patient was asked to fixate on a distant object or attempt to relax accommodation completely. We would now call this static retinoscopy. Dynamic retinoscopy is when the patient is asked to fixate with both eyes (binocularly) on a near object. The technique was first identified in principle by A. J. Cross in 1902 but it took some years to become a common method. The near object could be something as simple as a book held in the patient's hand but later retinoscopes were designed with fixation targets incorporated in the instrument itself.
In 1901 Wolff introduced the first electric retinoscope.
The first self-illuminated retinoscopes contained a tiny lamp bulb that shone a spot of light into the eye. Later 'variable vergence' models could produce the effect of the spot being reflected by a plane mirror or, less commonly, a concave mirror.
Sometimes a drawing from a trade catalogue is clearer to look at than a photograph of the actual object. Let's look at two from the 1930s.
The right image shows the Margaret Dobson Dynamic Retinoscope. This instrument automatically compensated for the working distance at which the patient was trying to achieve binocular fixation. The spot was produced by a spiral filament and was rendered slightly divergent by passing through condensing lenses before being reflected into the eye using a plane mirror. A revolving disc on the instrument contained a choice of seven fixation charts designed to be held the normal reading distance of 13 inches away from the patient. An eighth target was a blank shutter. This cut off all target illumination and allowed the instrument to be used for a traditional static retinoscopy test instead. The target on show in the drawing is a horse for use when examining children. To make them accommodate the image the optician would ask the child questions such as 'Does the horse have an eye?'
The Turville-Pascal 'Dynascope' (Dynamic Retinoscope) from 1931 was a collaborative effort aimed at countering the errors known to be introduced by the instrument itself in dynamic retinoscopy before that date. The lead designer was a Fellow of the British Optical Association, Mr A. E. Turville (1890-1965), who had the following to say about the technique:
As is the case with all other methods and techniques in refraction the operator needs experience before the full advantages of Dynamic Retinoscopy are appreciated. Too often a method or instrument is discarded because at first it did not seem to properly fulfil its promises. The fault, often, is not in the instrument, or technique, but in lack of experience in using it. Doubtless, years ago, many condemned Static Retinoscopy because they failed, through lack of experience, to appreciate the diagnostic value of what was seen.
Quoted from The Technique of Dynamic Retinoscopy (1932)
In the course of a 1930s eye examination dynamic retinoscopy followed the subjective distance test and did not precede it, as was the case with static retinoscopy. It was only concerned with the spherical element, the cylindrical correction having already been found.
Since an astigmatic eye produces a linear fundus reflex, a rectangular beam or streak of light rather than a spot could be more useful in detecting astigmatism. Early pioneers produced their own mirrors with a slit in the middle to convert the spot into a linear beam.
The father of streak retinoscopy was Jack C. Copeland (1900-1973) who introduced the first variable vergence streak retinoscope in the early 1920s, apparently after accidentally damaging the bulb of a Wolff Spot retinoscope when he dropped it. He patented his design in 1927. The instrument produced its own linear beam which could rotate through all the ocular meridians. He went on to spend his life teaching its use, latterly at the Medical College of Wisconsin.
Bausch & Lomb, whom Copeland joined as technical consultant in 1927, took on the patented design and ran with it for the next half century. In the mid 20th century this was available in Britain as the Pulzone Streak Retinoscope. The practitioner looked through the peephole in the head of the instrument along the beam of light projecting out of the other side. By moving the sleeve up or down he could change the focus (vergence) of the beam and by turning the sleeve he could rotate the projected streak.
Hand-held retinoscopes began to be overtaken in the 1970s by auto-refractors making use of infra-red light, however, all optometrists still train to use a retinoscope and candidates in the College's Scheme for Registration are expected to use one in their Final Assessment.
In recent decades practitioners have had to learn how to interpret the results of retinoscopy in new situations, for example the eyes of many post-operative patients give off peculiar reflexes in the weeks following corneal refractive surgery.
Although the theory and practice of the method of retinoscopy has undergone considerable change since the 1870s, the pace of development in the instruments themselves has been much slower. Retinoscopes remain essentially simple pieces of equipment and it is that simplicity together with portability and flexibility in use that means they still have a bright future.
Some Useful Sources for Historians of Retinoscopes:
(See also the sources mentioned at the end of our web feature on ophthalmoscopes)
All these titles are available in the College Library or within the files of the BOA Museum.