What is Optometry. Materials

The word, ‘‘optometry’’ was introduced to ophthalmology in 1904 and is important as an adjunct to that medical specialty because it focuses on examination of the eyes, analysis of vision, and the prescription of corrective or preventive measures for any deficits or problems. An optometrist will refer a patient to an ophthalmologist when pathologies of the eye are found during examination of visual function. Most of the technology used in optometry involves measurement and lenses. The only pharmaceuticals used are pupil dilators, drugs used to make the pupils larger so that the posterior parts of the eye can be examined.

Optometry developed from a split in the optical profession that took place in the nineteenth century that resulted two kinds of opticians, refracting and dispensing. Refracting opticians became optometrists. In Canada and the u.S., an optometrist must obtain an undergraduate degree and then undertake four years of specialized graduate education plus clinical and resident training to become an OD, or doctor of optometry.

By contrast, a dispensing optician’s training is from six months to two years (which varies by location), and does not necessarily require formal education. The optician can apprentice with an ophthalmologist, optometrist, or another optician. An optician makes or dispenses lenses and eyeglasses; an optometrist performs eye examinations.

Technologies of optometry can be subdivided into two categories: development of eyeglasses, contact lenses, and coatings; and instruments of measurement.

The idea that a convex lens could be used to magnify was known to the ancients. The use of a lens as a magnifying glass to aid vision is attributed to Roger Bacon in Opus Majus (major work), written in 1268. Soon after, Italian monks D’Armate (1284), da Rivalto (1306), or possibly a competitive contemporary, da Spina, invented eyeglasses. This early device was hinged and held two magnifying spheres that rested uncomfortably on the nose without support.

In 1303, Bernard of Gordon (Montpellier, France) fashioned a pair of spectacles with a fixed bar, but it took 400 years of various experiments, from ribbons looped around the ears, to weights that balanced glasses on the nose, until a design was engineered to allow the glasses enough stability to free the reader’s hands. Corrective lenses were developed in the early seventeenth century.

The popularity of spectacles grew throughout Europe, but because they were promoted by itinerant peddlers with little or no education, medical professionals were hesitant to endorse such products. Ironically, the growth of optometry was not because of oculists or physicians but in spite of them. Each time these unlicensed vendors and peddlers were able to fit spectacles to someone visually impaired, it increased their knowledge and skill.

By the nineteenth century, telescopes, microscopes, and cameras, and optical instruments required lenses for their use. However it was the adaptation of these lenses to that gave optometry its refined technology. An early ophthalmometer that used a small telescope was developed by E. Javal and H. Schiotz in Germany in 1881 and later modified into an astigmometer. The ophthalmoscope was invented by Hermann Von Helmholtz (Germany) in 1851; the retinoscope was introduced by Cuignet in 1873 in France; and Placido’s keratoscope appeared in 1882. By the beginning of the twentieth century these instruments were in place to fit the established practices ofoptometrists.

The greatest changes to optometry in the twentieth century were in modifications of the instruments for diagnosis and the proliferation of materials that rendered lenses—for both glasses and instruments of measurement—thinner, lighter, more durable, safer, and more accurate. The four major instruments used by optometrists are the retinoscope, or skiascope, the slit lamp, the phoropter (introduced in 1938), and the ophthalmoscope.

The retinoscope illuminates the retina. It is used to test astigmatism, farsightedness, and nearsightedness. Early machines used a light source directed from a mirror. In the early 1900s, the technique was refined and termed spot retinoscopy. The operator recorded the direction of movement of the light on the retinal surface and the angle of the light rays that emerged as a reflex from the patient’s eye, a phenomenon known as refraction.

In 1926, ophthalmologist Jack Copeland inadvertently dropped the spot retinoscope he was using. In what might be considered a serendipitous event, he recognized that the damaged equipment could still be used and that it produced a clearer image of the patient’s eye. Thus the streak retinoscope was invented. He patented it in 1927, and it remained unchanged until 1968 when a cordless retinoscope was developed by Optec (the Optec 360).

In the twentieth century, independent light sources—an electric bulb or battery-operated machine—were employed instead of mirrors. In 1992, a new retinoscope was developed which did not require measurement by the operator at all. Instead, the patient’s eye was measured against computerized predetermined calibrations and then transposed into meaningful data that was used by the optometrist to determine the patient’s prescription if correction were needed and the lenses that would be required.

The slit lamp looks like a very elaborate microscope. It sits on a table and has a chin and headrest attached. The light source with controls is on a movable arm and the operator is able to adjust brightness, the size of the beam of light, and insert different filters. It uses a set of hand-held lights directed at the front of the patient’s eye and examines the eyelid, the sclera (white of the eye), conjunctiva (mucous membranes), iris (colored part of the eye), lens, and the cornea (outer covering). It is called a slit lamp because its light source shines as a slit.

This specialized magnifying microscope-type device was invented by Allvar Gullstrand in 1911 in Sweden. Later, attachments were added to include a camera for taking photographs, a tonometer for measurement of intraocular pressure (significant in glaucoma), a pachymeter to measure corneal thickness, and a laser treatment module for the ophthalmologist. It also had changeable lenses.

The phoropter is imposing in appearance. It is suspended from a bar and looks like a giant pair of glasses with five lenses on each side. The machine is used to test vision by moving sets of lenses in front of the patient’s eye. Traditional phoropters are used to both measure and correct vision in order to derive an optical prescription for the patient. In the last decade of the twentieth century, a MEMS (microelectromechanical semiconductor)-based adaptive optics phoropter (MAOP) was developed that used adaptive-optics technologies and a deformable mirror.

Interestingly, this technology was originally developed for astronomy applications. Of benefit to the optometrist is that the newer machine requires less space and automatically calculates the numbers required for the vision correction prescription.

The von Helmholtz ophthalmoscope consisted of a handle and a group of lenses that could be interchanged. It is an instrument that allows the doctor to look inside a person’s eye and view the optic disc. Modern ophthalmoscopes are either direct or indirect. The direct is a hand-held instrument with a battery-powered light source.

It has a series of lenses that are dialed in to focus the doctor’s view of the central retina. The indirect ophthalmoscope is used to examine the entire retina. This instrument is worn on the doctor’s head and another lens is placed in front of the patient’s eye. The ophthalmoscope is used by both optometrists and ophthalmologists.

Materials. Eyeglasses were made exclusively from glass until the 1950s when the revolution in plastics began. Two companies pioneered the development of a thinner, lighter, and flatter lens made from plastic: American Optical (AO) and Columbia Southern Chemical Company. In 1937, AO produced a polymethyl methacrylate (PMMA), a hard plastic material that could be molded for lenses, but it was not scratch resistant and often distorted under high temperatures.

During World War II, Columbia Southern Chemical Company produced a series of 200 polymers. From these, number 39, the chemical composition of which is allyl diglycol carbonate (ADC), had ideal qualities for a lens. It did not soften or distort at high temperatures and was scratch resistant. It was cast rather than molded. Named CR-39, this became the industry standard for eyeglass and contact lenses.

In 1971, a flexible plastic contact lens containing a gel was developed that allowed the wearer to change the lens. The advantage was cosmetic and economical. Eye color could be changed with the lens and the price was greatly reduced, thus concerns about loss or breakage were less of an issue. In 1978, a rigid gas permeable lens (RGP) was developed that could be custom fitted to the cornea.

By 1983, they were available for commercial distribution. Although they were hard, they allowed for the exchange of oxygen on the surface of the eye and were particularly advantageous to people who had undergone surgery for cataract removal. An extended-wear plastic, developed in 1981 allowed the wearer to keep the lens on the eye for longer than 24 hours and even sleep with it. These could remain as long as one week without change.

A few years later, the disposable contact lens was on the market. By the late 1990s, the rigid gas-permeable contact lenses formula of fluorosili-cone acrylate was modified. At the turn of the century, contact lens possibilities included disposable tinted lenses that could be used for two weeks; disposable lenses with ultraviolet ray protection; and multifocal disposable soft lenses that made a contact ‘‘bifocal’’ possible, thereby moving from eyeglasses and contacts to contacts alone.