Dry eye syndrome
Dry eye disease, also known as keratoconjunctivitis sicca, is the condition of having dry eyes. The term dry eye syndrome was formerly used, but is now avoided following advances that have established it as a distinct disease entity.
Symptoms of dry eye include dryness in the eye, irritation, redness, discharge, blurred vision, and easily fatigued eyes. Symptoms range from mild and occasional to severe and continuous. DED can lead to blurred vision, instability of the tear film, increased risk of damage to the ocular surface such as scarring of the cornea, and changes in the eye including the neurosensory system.
Dry eye occurs when either the eye does not produce enough tears or when the tears evaporate too quickly. This can be caused by age, contact lens use, meibomian gland dysfunction, pregnancy, Sjögren syndrome, vitamin A deficiency, omega-3 fatty acid deficiency, LASIK surgery, and certain medications such as antihistamines, some blood pressure medication, hormone replacement therapy, and antidepressants. Chronic conjunctivitis such as from tobacco smoke exposure or infection may also lead to the condition. Diagnosis is mostly based on the symptoms, though several other tests may be used. Dry eye disease occasionally makes wearing contact lenses impossible.
Treatment depends on the underlying cause. Artificial tears are usually the first line of treatment. Wrap-around glasses that fit close to the face may decrease tear evaporation. Looking carefully at the medications a person is taking and, if safe, altering the medications, may also improve symptoms if these medications are the cause. Some topical medications, or eye drops, may be suggested to help treat the condition. The immunosuppressant cyclosporine may be recommended to increase tear production and, for short-term use, topical corticosteroid medications are also sometimes helpful to reduce inflammation.
Dry eye disease is a common eye disease. It affects 5–34% of people to some degree depending on the population looked at. Among older people it affects up to 70%. In China it affects about 17% of people. The phrase "keratoconjunctivitis sicca" means "dryness of the cornea and conjunctiva" in Latin.
Definitions
In the Tear Film & Ocular Surface Society Dry Eye Workshop II report, dry eye was defined by a multidisciplinary and transnational committee as:According to the TFOS DEWS III, It was agreed that the definition did not require radical change, given the updated understanding of disease pathology and the tear film. However, the revised definition emphasized the intrinsic role of both the ocular surface tissues as well as the tear film in maintaining homeostasis leading to the following updated wording:
The TFOS DEWS definitions have contributed to establishing a clear characterization of dry eye as a disease. Whereas it was formerly described as a syndrome because of the limited understanding of its etiology, subsequent advances in research have clarified its diagnostic features, natural history, and therapeutic responses, supporting its recognition as a distinct disease entity.
Signs and symptoms
Typical symptoms of dry eye disease are dryness, burning and a sandy-gritty eye irritation that gets worse as the day goes on. Symptoms may also be described as itchy, stinging or tired eyes. Other symptoms are pain, redness, a pulling sensation, and pressure behind the eye. There may be a feeling that something, such as a speck of dirt, is in the eye. The resultant damage to the eye's surface increases discomfort and sensitivity to bright light. Both eyes usually are affected.There may also be a stringy discharge from the eyes. Although it may seem contradictory, dry eye can cause the eyes to water due to irritation. One may experience excessive tearing such as if something got into the eye. These reflex tears will not necessarily make the eyes feel better since they are the watery tears that are produced in response to injury, irritation, or emotion which lack the lubricating qualities necessary to prevent dry eye.
Because blinking coats the eye with tears, symptoms are worsened by activities in which the rate of blinking is reduced due to prolonged use of the eyes. These activities include prolonged reading, computer usage, driving, or watching television. Symptoms increase in windy, dusty, or smoky areas, in dry environments with high altitudes including airplanes, on days with low humidity, and in areas where an air conditioner, fan, heater, or even a hair dryer is being used. Symptoms reduce during cool, rainy, or foggy weather and in humid places, such as in the shower.
Most people who have dry eyes experience mild irritation with no long-term effects. However, if the condition is left untreated or becomes severe, it can produce complications that can cause eye damage, instability of the tear film, neurosensory changes, impaired vision, or in the loss of vision.
Risk factors
Excess screen time on computers, smartphones, tablets, or other digital devices can cause dry eye. "Humans normally blink about 15 times in one minute. However, studies show that we only blink about 5 to 7 times in a minute while using computers and other digital screen devices. Blinking is the eye's way of getting the moisture it needs on its surface."Aging is one of the most common contributing factors to dry eye, as tear production declines with age. Several classes of medications, both prescription and over-the-counter, have been hypothesized to be one of the key contributros to dry eye, especially in the elderly. In particular, anticholinergic medications, which also cause dry mouth, are believed to promote dry eye. Dry eye may also be caused by thermal or chemical burns, or by adenoviruses. A number of studies have found that people with diabetes have an increased risk for the condition.
About half of all people who wear contact lenses complain of dry eyes. There are two potential connections between contact usage and dry eye. Traditionally, it was believed that soft contact lenses, which float on the tear film that covers the cornea, absorb the tears in the eyes. The connection between a loss in nerve sensitivity and tear production is also the subject of current research.
Dry eye also occurs or becomes worse after laser-assisted in situ keratomileusis and other refractive surgeries, in which the corneal nerves that stimulate tear secretion are cut during the creation of a corneal flap. Dry eye resulting from these procedures usually resolves after several months, but it can be permanent. Individuals considering refractive surgery should be aware of this potential complication.
An eye injury or other problem with the eyes or eyelids, such as bulging eyes or a drooping eyelid may lead to keratoconjunctivitis sicca. Eyelid disorders may disrupt the complex blinking motion necessary to distribute tears evenly.
Abnormalities of the mucin tear layer resulting from vitamin A deficiency, trachoma, diphtheric keratoconjunctivitis, mucocutaneous disorders, and certain topical medications are also implicated in keratoconjunctivitis sicca.
Individuals with keratoconjunctivitis sicca exhibit elevated levels of tear nerve growth factor . NGF on the ocular surface may play a significant role in the inflammation associated with dry eyes.
Seasonal variations in the manifestation of dry eye have also been reported.
The use of eye make-up products is another influencing factor. Although eye cosmetics have a long history and have been investigated for years, comprehensive reviews on their role in dry eye disease and in ocular surface and adnexal disease were first published in 2022 and 2023, respectively.
Pathophysiology
Having dry eyes for a while can lead to tiny abrasions on the surface of the eyes. In advanced cases, the epithelium undergoes pathologic changes, namely squamous metaplasia and loss of goblet cells. Some severe cases result in thickening of the corneal surface, corneal erosion, punctate keratopathy, epithelial defects, corneal ulceration, corneal neovascularization, corneal scarring, corneal thinning, and even corneal perforation.Another contributing factor may be lacritin monomer deficiency. Lacritin monomer, the active form of lacritin, is selectively decreased in aqueous deficient dry eye, Sjögren syndrome dry eye, contact lens-related dry eye, and in blepharitis. The ocular surface microbiome, composed of a diverse community of microorganisms, has been implicated in the pathogenesis of dry eye disease, potentially influencing ocular surface inflammation and homeostasis.
Diagnosis
Symptom assessment is a key component of dry eye diagnosis – to the extent that many believe dry eye disease to be a symptom-based disease. Several questionnaires have been developed to determine a score that would allow for a diagnosis. The Ocular Surface Disease Index is the most frequently used questionnaire in clinical practice and research.Some tests allow patients to be classified into one of two categories, "aqueous-deficient" or "hyperevaporative". Diagnostic guidelines were published in 2007 by the Dry Eye Workshop, updated by the Dry Eye Workshop II in 2017. A slit lamp examination can be performed to diagnose dry eyes and to document any damage to the eye. When realizing this test, the practitioner is testing the eyelid margin.
A Schirmer's test can measure the amount of moisture bathing the eye. This test is useful for determining the severity of the condition. A five-minute Schirmer's test with and without anesthesia using a Whatman #41 filter paper 5 mm wide by 35 mm long is performed. For this test, wetting under 5 mm with or without anesthesia is considered diagnostic for dry eyes.
If the results for the Schirmer's test are abnormal, a Schirmer II test can be performed to measure reflex secretion. In this test, the nasal mucosa is irritated with a cotton-tipped applicator, after which tear production is measured with a Whatman #41 filter paper. For this test, wetting under 15 mm after five minutes is considered abnormal.
A tear breakup time test measures the time it takes for tears to break up in the eye. The tear breakup time can be determined after placing a drop of fluorescein in the cul-de-sac.
A tear protein analysis test measures the lysozyme contained within tears. In tears, lysozyme accounts for approximately 20 to 40 percent of total protein content.
A lactoferrin analysis test provides good correlation with other tests.
The presence of the recently described molecule Ap4A, naturally occurring in tears, is abnormally high in different states of ocular dryness. This molecule can be quantified biochemically simply by taking a tear sample with a plain Schirmer test. Utilizing this technique it is possible to determine the concentrations of Ap4A in the tears of patients and in such a way diagnose objectively if the samples are indicative of dry eye.
The tear osmolarity test has been proposed as a test for dry eye disease. Tear osmolarity may be a more sensitive method of diagnosing and grading the severity of dry eye compared to corneal and conjunctival staining, tear break-up time, Schirmer test, and meibomian gland grading. Others have recently questioned the utility of tear osmolarity in monitoring dry eye treatment.