discovering dry eye
The History of Dry Eye Diagnosis and Management
BY BARBARA CAFFERY, OD
While trying to propose a new hypothesis for dry eye disease, I decided to take a look at the past. Until the 17th century, the conjunctiva was considered to be inherently wet. The problems of the epiphora were of interest then, but poorly understood. In the fifth century B.C., the belief was that tears came directly from the brain. In 1609, Casserius postulated that tears pass through the lamina cribrosa. That same year, Wathan argued that tears traveled through the nerves to the ocular surface. In 1662, this concept changed when Steno discovered that tear ducts actually join the lacrimal gland to the eye.
The mechanism of secretion was not proposed until 1851, when researchers produced salivary hypersecretion by electrical stimulation. They postulated that the same technique would apply to the lacrimal gland. Twenty years later, it was established that sympathetic nerves control the basal lacrimal secretions and the parasympathetic nerves control the acini and, therefore, direct hypersecretions.
Even in ancient Greece, it was known that a collyrium instilled in the eye can be observed in the nose and mouth, thus initiating the Jones' test. To ensure the movement of fluid to the mouth, saccharine, quinine and sodium chloride were used. In the 20th century, dyes such as mercurochrome, rose bengal and fluorescein were instilled to observe the ocular surface.
Treating the Disease
In 1900 B.C., while surgeons decided that the lacrimal gland should be treated with a knife, others believed that lacrimal dysfunction was best treated by rubbing the eyes for four days with a mixture of honey, antimony and dust. Early in the fifth century, oat herbs were placed on the eye to treat dry eye disease, and in the 11th century, topically applied grape wine ashes, vinegar and honey were used to treat ocular surface disease.
Tear substitutes using sodium chloride were invented in the early 1900s, and 30 years later, more viscous solutions were made from gelatin and methyl cellulose. Secretagogues were invented in the 1920s, and pilocarpine was also used, but found to be ineffective over the long term. The hormones estrogen and androgen were investigated in the late 1940s, but showed equivocol results. More recently, in the 1980s, two peptides extracted from a South American toad and a Mediterranean octopus proved useful for some dry eye conditions. However, even with all of these discoveries, there are still many stones left unturned.
What Is Different Today?
Today, we have a much greater understanding of the creation and secretion of the tear film, including the basic physiology of the lacrimal gland, the epithelia of the conjunctiva and cornea, and the meibomian glands. However, there remain many questions that need to be answered, such as: What causes the lacrimal gland to shut down when parts of the gland are still functioning? Why do the meibomian glands fail to maintain a clear and easy secretion? What is the initial stimulus in autoimmune-related dry eye?
When we analyze tear film, we believe that our Schirmer testing and staining techniques are relevant and valid, but is this true? Sometimes, our treatment systems seem no further ahead than the ones used in the oats and honey era.
History shows that we have come a long way in understanding dry eye, but the past also makes it clear that there is a great deal more to learn.
With critical observations and disciplined research, we will advance our understanding, and even create breakthroughs in the field of dry eye.
Dr. Caffery has practiced optometry in Toronto, Canada, in a group setting dedicated to contact lens and tear film research since 1977.