Ophthalmoscopes (part 1)
The principal diagnostic test, examining the eye for disease.
The principal diagnostic test, examining the eye for disease.
The ophthalmoscope is the staple instrument of the optometrist. Introduced in the 1850s it was the first proper device for examining the interior of the human eye by means of a beam of light which illuminates otherwise invisible tissues.
Here follows a brief history of the ophthalmoscope, developing original notes prepared by Mr Richard Keeler, HonFCOptom (special adviser to the museum on ophthalmic instruments).
Introduction: Helmholtz's Eye Mirror
It is now more than 160 years since Hermann von Helmholtz's 'discovery' of the ophthalmoscope in 1851. He called it an Augenspiegel (eye mirror): The name 'ophthalmoscope' (eye-observer) did not come into common use until three years later, in 1854. At the time Helmholtz, who was only 29, was a professor of physiology and he wanted to demonstrate to his students why the pupil of the eye sometimes appeared black and at other times light.
On the left is an early Helmholtz Ophthalmoscope from 1851. Such instruments are extremely rare and unfortunately the BOA Museum does not yet possess one. The image is reproduced courtesy of our sister college, the Royal College of Ophthalmologists, as is the portrait of Helmholtz as a young man.
Below that is a more familiar portrait of the inventor, representing his appearance later in life, together with a diagram of how the instrument worked.
Prior to his invention there was much speculation as to what lay behind the black hole of the pupil of the eye. Until 1810 there had been many theories about why the eye became luminous under certain conditions. Some thought that the fleeting luminosity was a phenomenon of phosphorescence; others speculated that light absorbed during the day gave off light at night, while others thought that it was the result of activity similar to a firefly and that it was electricity emitted by the retina.
Bénédict Prévost, Professor of Philosophy at Montaubon in France, explained in 1810 that the luminosity could only be observed when light entered the eye from without.
Some important definitions:
Fundus = The interior of the eye as it appears through an ophthalmoscope when illuminated. It includes the retina, the retinal blood vessels, foveal depression and optic disc. It has a distinctive orange/red colour caused by the choroidal vessels and can vary in shade according to the patient's race. In some darker-skinned races the fundus may appear almost grey.
On the right is a drawn observation of the iris produced by the Hamblin Artist's Department, 1930. It shows the optician's view approaching the fundus through the pupil when the ophthalmoscope was still perhaps a foot away from the patient.
Retina = The light-receptive membrane at the innermost region of the eye.
On the right is a drawing of the inside of the eye, known as a fundus picture, based on observations made with an ophthalmoscope. This particular drawing shows a detached retina, a major condition requiring immediate surgery.
Fovea = The thinnest part of the retina and the eye's point of fixation.
Earlier Observations of the Fundus
Before Helmholtz there had been a number of observers of the fundus in both animals and humans.
In 1704 Jean Méry noticed that retinal vessels in the fundus of a cat's eyes became distinctly visible when the animal was placed under water.
Jan Purkinje (shown to the left, contemplating a skull) observed the fundus of a dog and then the human eye by using his myopic spectacles (acting as a concave mirror) which reflected light into the eye from a candle placed behind the subject. In 1825 he published his detailed findings in Latin but was unrecognised for his contribution to the knowledge until many years later.
Ernst Brücke in 1846 gave an accurate explanation of the red colour of the luminous pupil but it was William Cumming, a young ophthalmologist at the Royal London Ophthalmic Hospital (later to become the Moorfields Eye Hospital) who in 1846 published a paper stating that every eye could be made luminous if the axis from a source of illumination directed towards a person's eye and the line of vision of the observer were coincident.
Was the first ophthalmoscope actually British?
Charles Babbage, the mathematic genius and inventor of what many consider to be the forerunner of today's computer, his analytical machine, was the first to construct an instrument for looking into the eye. He did this in 1847 but when showing it to the eminent ophthalmologist Thomas Wharton Jones he was unable to obtain an image with it and, thus discouraged, did not proceed further. Little did he know that his instrument would have worked if a minus lens of about 4 or 5 dioptres had been inserted between the observer's eye and the back of the plano mirror from which two or three holes had been scraped. Some seven years later it was his design and not that of Helmholtz which had been adopted.
The image to the right shows a reconstruction of Babbage's ophthalmoscope, c. 1847. No actual example survives but this replica was made for the museum in 2003, based upon Wharton Jones' written description.
Dr. Helmholtz, of Konigsberg, has the merit of specially inventing the ophthalmoscope. It is but justice that I should here state, however, that seven years ago Mr. Babbage showed me the model of an instrument which he had contrived for the purpose of looking into the interior of the eye. It consisted of a bit of plain mirror, with the silvering scraped off at two or three small spots in the middle, fixed within a tube at such an angle that the rays of light falling on it through an opening in the side of the tube, were reflected into the eye to be observed, and to which the one end of the tube was directed. The observer looked through the clear spots of the mirror from the other end. This ophthalmoscope of Mr Babbage, we shall see, is in principle essentially the same as those of Epkens and Donders, of Coccius and of Meyerstein, which themselves are modifications of Helmhotlz's.
Wharton-Jones, T., 1854, 'Report on the Ophthalmoscope', Chronicle of Medical Science (October 1854).
Rapid growth in the number of designs, but still just three essential design elements
The use of the ophthalmoscope grew rapidly. Already in the 1860s users of the instrument called themselves 'ophthalmoscopists'. In 1864 Dr A. M. Rosebrugh even showed the Canadian Institute how to take photograph of the fundus by reflecting its image onto a sensitised plate - one of the first ever fundus cameras!
By 1880 Landolt and Snellen had collected 86 types of ophthalmoscope and by the time Helmholtz died in 1894 a great number more had appeared, many designed by the best-known practitioners of the day. On the occasion of the 50th anniversary of the ophthalmoscope (1901) an exhibition was held in Atlantic City USA, where no fewer than 140 different designs were shown. By 1913 Edward Landolt reported that 200 models had been produced.
Helmholtz wrote at length about his ophthalmoscope and demonstrated that there were three essential elements in its construction:
These three elements hold firm today. Of the three, the source of illumination has undergone perhaps the greatest change.
Sources of illumination
Helmholtz used a naked candle. Other users quickly replaced this by the gravity-fed oil lamp and then the Argand gas-burning lamp. Attempts were made to harness the source of illumination to the optical viewing system, thereby eliminating one of the variables of alignment. Lionel Beale's ophthalmoscope of 1869 is perhaps the best known example of this.
Our pictures show a complete example in the collection of the Royal College of Ophthalmologists and (to the left) a Beale candle holder from about 1880 in the BOA Museum collection.
In 1879 Thomas Edison was working on his incandescent bulb and this was the start, a few years later, of a radical change in the construction of the ophthalmoscope.
The drawing on the left shows the first instrument to use a bulb within the body of the ophthalmoscope. It was created by Dr William Dennet who presented his slender-looking invention to the American Ophthalmological Society in 1885.
The idea was sound but the early technology was unreliable, with a variable and short bulb life. Dennet's invention was shortly followed by three other designs, by Thomas Reid of Glasgow, Sir James McKenzie Davidson of Aberdeen and Henry Juler of London, all in the same year - 1886.
Juler's design involved attaching a light source to the outside of the ophthalmoscope body, close to the mirror with the miniature bulb pointing towards the centre of the mirror aperture. Sight hole flare was a big problem and the life of the bulb was still short-lived.
The drawing on the right shows the electric version of Juler's ophthalmoscope and, beside it, the reverse side of an earlier, non-illuminated, version of the same instrument from 1882.
By the turn of the twentieth century bulb construction and reliability had improved. In 1900 Hugo Wolff produced an interesting ophthalmoscope using a long straight filament bulb which could be rotated within the instrument. By turning the handle a clear or diffuse patch of light could be projected on the fundus. The instrument was not (as the straight filament bulb might imply) used as a retinoscope. This instrument had another unusual feature in that the wheel of lenses was situated in front of the mirror and not behind it as on other ophthalmoscopes.
Continue to Ophthalmoscopes (part 2)