Most people associate the eye examination with 'those funny glasses the optician makes you wear'. These are called trial frames and, despite competition from automatic refracting units, they remain one of the optometrist's most important pieces of kit.
The BOA Museum currently possesses over a hundred different types of trial frame - not just the 'simple', but also the 'Accurist', the Armagnac, Bjerke, Fink, Freeman, Moorfields, Moswheel, the much-used Oculus, the 'Perfection' or the distinctive-looking Skeoch, the STOCO, Swann-Cole, Tosswill or the 'Universal', but a fair few of them still need to be identified.
Whilst endeavouring to keep them as lightweight as possible, designers have nevertheless added to the many functions these instruments can perform.
Before trial frames could exist you needed to have such things as trial lenses, but those did not become standardised before the adoption of the dioptre as the unit of measurement in 1875. Prior to that it was possible to use a lens trier as a means of trying out lenses of different focal lengths.
The lens trier consisted of a number of individually mounted lenses that folded into their handle-cum-carrying case made of horn or tortoiseshell. ‘Trial boxes’ like these were first used in England by the optician George Cox in 1838 and soon grew in size from eight lenses to as many as sixty, but not all fixed within the same handle. The person carrying out the examination (not necessarily anyone with a professional qualification) could flip between lenses quickly and conveniently, but the resulting prescription might be limited depending upon the powers of lens available in the box set. Lens triers (from the verb ‘to try’) continued in use until the end of the Victorian era and later still in some outlying regions and the British Imperial Dominions.
Even when at the height of their popularity lens triers were considered inadequate for the task by some practitioners. In 1863, a student of the ophthalmic surgeon William Bowman wrote with disdain that ‘errors of refraction were so little understood that a small tortoise-shell case, which could easily be carried in a trousers' pocket, containing half a dozen convex and concave spherical lenses, was held to comprise a sufficient stock for every trial’.
The first trial frames were simply an accessory in the ophthalmic optician's trial case of test lenses. Some trial lenses came in metal rims with a handle that might also have the lens power engraved upon it and a + or - sign to indicate the set of lenses to which it belonged. It was a logical step from this for some sets to provide a long handle with a lens clip on the end to hold just a single lens. This idea was then developed, via a lorgnette-type contraption that didn't last long, into a wearable frame with spectacle sides and at the front two grooved receptacles and a forked or sprung clip to hold the trial lenses in place.
The simple drop-cell was easier to use. The lenses rested in the grooves of their own accord and the practioner did not need to touch the frame. By now a half scale on an 'ivory' (usually plastic) crescent was present, allowing for visual axis readings. This type of trial frame remained popular for a long time and would be as typical of the year 1900 as of the year 1930.
Sutcliffe's Trial Frame from 1906 consisted of two round eyes dependent from an adjustable cylindrical bar. There are now double lens cells and engraved scales.
The frame to the right is for more than momentary use and represents a different meaning to the term 'trial frame'. Designed to hold prismatic lenses, it was for the patient to trial (i.e. try out) the lenses deemed likely to be suitable for a period of time and, consequently, the lenses were screwed into the frame and there was no need for any scales. A trial frame of this type was designed by Krusius in 1914 but the design of the item pictured here is too simple to enable a positive identification with a known maker.
The ophthalmic optician J. H. Sutcliffe also invented a 'self-adjusting spring trial-frame' in association with C. W. Dixey and Sons using the sort of telescopic spring bar as familiar to collectors of astigmatic pince-nez. This was shown at the Oxford Ophthalmological Congress of 1915 where it was suggested that its simple design meant that the patient might be invited to put on the frame himself and its banana-shaped plaquets would eliminate all wobble.
This full-rim trial frame is typical of those used throughout the middle two quarters of the twentieth century. It's shiny white metal could belie its age. The same pattern of front appears to have been available with a wide range of side designs and it could also be obtained as a headband model.
Bishop Harman's Trial Frame Gauge, manufactured and supplied by Theodore Hamblin Ltd was an alternative to a frame with its own scales. The scales could be dropped into the vacant cells just like the lenses themselves. This particular example was used at the Glasgow Eye Infirmary.
The importance of the instrument to the left is indicated by the carefully constructed rigid case in which it was supplied. It includes two milled-wheel millimetre scales perpendicular to the joints for measuring the distance of the plane of the eyeframe rim from the corneal vertex. The sides could be raised or lowered a little in cases where the patient's ears were unusually high or low. K. Bjerke gave a paper on trial frames in German to the International Congress of Ophthalmology in St Petersburg in 1914.
This detail from another Zeiss trial frame of about 1925 (or maybe a bit earlier) shows the adjustable nasal height setting. It is made of aluminium and includes a tortoiseshell nose pad.
Meanwhile the mid 20th century frame shown below is adjustable both for p.d. and for nasal height. It has a capacity of six trial lenses (two lenses in front of eyes and one behind). It also includes fold-away occluders to the sides, just to make sure that the patient is reading the letter chart with the correct eye!
In order to try out cylindrical lenses it was more convenient for at least one of the lens holders to be rotable. The trial frame below is typical of the first half of the 20th century, having been patented originally on 30th April 1895. It also has a capacity of six lenses though the holding mechanism is more like the clips we noted earlier. There is a double lens clip in front of the eyes and a single lens clip behind. The front clips revolve and would be ideal for holding a lens to test for the required amount of bifocal addition. It also has sliding curl sides of adjustable length.
The item shown next is not a trial frame but there is a distinct family resemblance! Trial frame technology led briefly to other innovations and facial measuring devices were produced that closely resembled them. The first was Javal's Universal Measuring Device of 1880 manufactured on his behalf by Rodenstock. It proved too expensive. Many optometrists in the early twentieth century still preferred to use an ordinary ruler.
In the 1930s special child frames were produced. They were a smaller size and were kept a simple as possible. Although the lens holder for each eye was just a simple drop cell the eye rim was often completed into a full circle to make the item more robust and perhaps more familiar to the wearer. In this American example that has not happened, but the tiny round lenses nevertheless have a thick metal rim.
Modern trial frames fit very snugly and are probably made of light plastic, however it is largely a matter of choice whether an optometrist will use one or an automatic refractor head. Having said that, the first refractors were little more than a glorified trial frame on an instrument arm.