orthoptics

orthoptics is the science concerned with ensuring that patients' eyes develop their full visual potential and keep working together throughout life.

During the latter part of the nineteenth century, Javal, in France, started using ocular exercises and training methods for squints, which were very time-consuming but sometimes effective. After many years, in 1896, Javal wrote, ‘The first time that I revealed my methods to von Graefe (the foremost ophthalmologist of his day) he astounded me by saying that people are not worth the effort. Life's experience has shown me that von Graefe was correct.’

In London, at the start of the twentieth century, Worth, an eye surgeon, used a modified stereoscope (amblyoscope), which presented separate images to each eye via two tubes so that the angle between these two images could be varied in an attempt to stimulate their fusion — again time-consuming. Maddox, working in Bournemouth with various ophthalmic instruments he had devised himself, found a new solution to the ever-increasing time needed to examine patients. He solved this problem by teaching his daughter Mary, who was already working as receptionist/secretary in his consulting rooms, to use the amblyoscope and other special tests for orthoptic assessment and treatment. Miss Maddox opened her own private clinic in 1928 and was soon joined by Sheila Mayou to form the Maddox– Mayou Orthoptic Training School. A year later Miss Maddox was invited to open an orthoptic clinic at the Royal Westminster Ophthalmic Hospital (which became the High Holborn branch of Moorfields Eye Hospital in 1947). The increasing numbers of orthoptists in training led to the Orthoptic Board being formed in 1934 to provide a syllabus and code of conduct. In 1937 the British Orthoptic Society was founded, with Miss Maddox as president and Miss Mayou as chairman.

By the late 1930s, the belief that orthoptic training methods could overcome the problems of faulty visual development in squinting children was being revised. It was proposed that squint resulted from a series of obstacles to the normal development of fusion and binocular single vision. Orthoptics was no longer presented as the definitive cure for squints, but as offering diagnosis and treatment for specific types of squint and visual impairment. Patching the preferred eye to stimulate vision in the deviating or lazy eye had been introduced to England empirically by Erasmus Darwin (Charles' grandfather) by 1801. Such occlusion therapy was widely applied after 1930, but it was not until the 1960s that its neuro-physiological basis was established.

A course in orthoptics takes three years of study. As well as optics and refraction it includes anatomy, physiology, neurology, and child development, ensuring that orthoptists are particularly suited to examine vision in very young children. This is necessary to allow appropriate therapy to be started within the sensitive period of visual development for optimal results.

Orthoptists are often a young child's first contact with medical personnel or hospitals, and it should be a happy occasion and one which the child will be eager to repeat. Visual acuity can be assessed at only a few months of age by special tests where the infant turns to look at a target of broad black and white stripes in preference to a uniformly grey target of equal luminosity. The width of the black and white stripes is successively reduced until the infant ignores the target. Young children, before they can read, can point to a letter on a card that matches one held up by the orthoptist. The familiar ‘Snellen’ letters are used for acuity testing in older children.

refractive error can be measured by orthoptists, but the prescribing of corrective lenses has to be done by the ophthalmologist or optometrist. Ocular movements are noted and the angle of squint measured. Convergence is checked, and an assessment is made of the quality of fusion of the two images and of stereopsis (detailed depth perception). Areas of fusion and of diplopia can be charted, and an accurate and repeatable graphic record can be made of defective ocular rotations. These basic tests, together with more specialized ones, allow diagnoses to be made and therapy started. Orthoptists supervise occlusion therapy for amblyopia, and teach exercises to improve binocular control and poor convergence. In latent squint, where the eyes cannot maintain binocular fixation under the stress of illness or tiredness, the tendency for the eyes to deviate can be controlled with prisms should ocular exercises prove insufficient.

Once qualified, orthoptists have a number of additional courses available. These include visual field and intra-ocular pressure measurements in glaucoma; biometric assessment with ultrasound of eyes for cataract extraction, so that the correct power of replacement intra-ocular lens is used; photography of eye movements; and fluorescent photography of ocular blood flow. Many of these supplemental skills are also exercised by optometrists; indeed some pre-and post-qualification courses are shared by orthoptists and optometrists. Nevertheless, when it comes to gaining the confidence and co-operation of infants and very young children during testing, the orthoptist reigns supreme.

Peter Fells

Bibliography

M. J. Revell (1971). Strabismus — a history of orthoptic techniques. Barrie and Jenkins Ltd., London.

See also eyes; eye movements; optometry; squint.