Keratoconjunctivitis Sicca
Also Know As Dry Eye
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Keratoconjunctivitis sicca
Keratoconjunctivitis sicca (KCS), also called keratitis sicca,[1] sicca syndrome,[1] xerophthalmia,[1] dry eye syndrome (DES),[1] or simply dry eyes,[1] is an eye disease caused by decreased tear production or increased tear film evaporation commonly found in humans and some animals[2]. Keratoconjunctivitis sicca is Latin and its literal translation is "dryness of the cornea and conjunctiva". It may be helpful to know that "sicca" is part of the English word "desiccate."
Symptoms
Typical symptoms of keratoconjunctivitis are dryness, burning[3] and a sandy-gritty eye irritation that gets worse as the day goes on.[1] Symptoms may also be described as itchy,[3] scratchy,[4] stingy[3] or tired[3] eyes. Other symptoms are pain,[5] redness,[5] a pulling sensation,[3] and pressure behind the eye[3]. There may be a feeling that something,[3] such as a speck of dirt,[5] is in the eye. The resultant damage to the eye surface increases discomfort and sensitivity to bright light.[3] Both eyes usually are affected.[6]
There may also be a stringy discharge from the eyes.[5] Although it may seem strange, dry eye can cause the eyes to water.[5] This can happen because the eyes are irritated.[5] One may experience excessive tearing in the same way as one would if something got into the eye.[5] These reflex tears will not necessarily make the eyes feel better.[5] This is because they are the watery type that are produced in response to injury, irritation, or emotion.[5] They do not have the lubricating qualities necessary to prevent dry eye.[5]
Because blinking coats the eye with tears,[5] symptoms are worsened by activities in which the rate of blinking is reduced due to prolonged use of the eyes[3]. These activities include prolonged reading,[1] computer usage,[1][5][3] driving,[3] or watching television[5][3]. Symptoms increase in windy,[5] dusty[5][3] or smoky (including cigarette smoke[5]) areas,[1][3] in dry environments[1][3], high altitudes including airplanes,[6] on days with low humidity,[3] and in areas where an air conditioner[5] (especially in a car[3]), fan,[3] heater,[3] or even a hair dryer[5] is being used. Symptoms reduce during cool, rainy, or foggy weather and in humid places, such as in the shower.[3]
Most people who have dry eyes experience mild irritation with no long-term effects.[5] However, if the condition is left untreated or becomes severe, it can produce complications that can cause eye damage,[5] resulting in impaired vision or (rarely[3]) in the loss of vision[5].
Symptom assessment is a key component of dry eye diagnosis - to the extent that many believe dry eye syndrome to be a symptom-based disease. Several questionnaires have been developed to determine a score that would allow for dry eye diagnosis. McMonnies & Ho dry eye questionnaire is the one that is often used in clinical studies of dry eyes. There are 14 questions that can give a score from 0 to 45. Scores above 14.5 are consistent with dry eye diagnosis.
Causes
Any abnormality of any one of the three layers of tears produces an unstable tear film, resulting in symptoms of keratitis sicca.[1]
Deficient tear production
Keratoconjunctivitis sicca is usually due to inadequate tear production.[1][3] The aqueous tear layer is affected, resulting in aqueous tear deficiency (ATD) or lacrimal hyposecretion.[1] The lacrimal gland does not produce sufficient tears to keep the entire conjunctiva and cornea covered by a complete layer.[3] This usually occurs in people who are otherwise healthy. Increased age is associated with decreased tearing.[1] This is the most common type found in postmenopausal women.[3][7]
Causes include idiopathic, congenital alacrima, xerophthalmia, lacrimal gland ablation, and sensory denervation.[1] In rare cases, it may be a symptom of collagen vascular diseases, including rheumatoid arthritis[3], Wegener's granulomatosis, and systemic lupus erythematosus.[1] Sjögren's syndrome[3] and autoimmune diseases associated with Sjögren's syndrome are also conditions associated with aqueous tear deficiency.[1] Drugs such as isotretinoin,[3] sedatives,[3][6] diuretics,[3] tricyclic antidepressants,[6] antihypertensives,[3] oral contraceptives,[1][3] antihistamines,[1][5][3] nasal decongestants,[5] beta-blockers,[1] phenothiazines,[1] atropine,[1], and pain relieving opiates such as morphine[6] can cause or worsen this condition. Infiltration of the lacrimal glands by sarcoidosis or tumors, or postradiation fibrosis of the lacrimal glands can also cause this condition.[1]
Abnormal tear composition
Keratoconjunctivitis sicca can also be caused by abnormal tear composition resulting in rapid evaporation[3] or premature destruction of the tears.[1] When caused by rapid evaporation, it is termed evaporative dry eyes.[3] In this, although the tear gland produces a sufficient amount of tears, the rate of evaporation of the tears is too rapid.[3] There is a loss of water from the tears that results in tears that are too "salty" or hypertonic. As a result, the entire conjunctiva and cornea cannot be kept covered with a complete layer of tears during certain activities or in certain environments.[3]
Additional causes
Aging is one of the most common causes of dry eyes.[5] This is because tear production decreases with age.[5] It may be caused by thermal or chemical burns, or (in epidemic cases) by adenoviruses. A number of studies have found that diabetics are at increased risk for the disease.[8][9]
An eye injury or other problem with the eyes or eyelids, such as bulging eyes or a drooping eyelid can cause keratoconjunctivitis sicca.[4] Disorders of the eyelid can impair the complex blinking motion required to spread tears.[6]
About half of all people who wear contact lenses complain of dry eyes.[5] This is because soft contact lenses, which float on the tear film that covers the cornea, absorb the tears in the eyes.[5] Dry eyes also occurs or gets worse after LASIK and other refractive surgeries, in which the corneal nerves are cut during the creation of a corneal flap.[5] The corneal nerves stimulate tear secretion.[5] Dry eyes caused by these procedures usually resolves after several months.[6] Persons who are thinking about refractive surgery should consider this.[5]
Abnormalities of the lipid tear layer caused by blepharitis and rosacea, and abnormalities of the mucin tear layer caused by vitamin A deficiency, trachoma, diphtheric keratoconjunctivitis, mucocutaneous disorders and certain topical medications are causes of keratoconjunctivitis sicca.[1]
Persons with keratoconjunctivitis sicca have elevated levels of tear nerve growth factor (NGF).[1] It is possible that this ocular surface NGF plays an important role in ocular surface inflammation associated with dry eyes.[1]
Diagnosis
Dry eyes can usually be diagnosed by the symptoms alone.[3] Tests can determine both the quantity and the quality of the tears.[6] A slit lamp examination can be performed to diagnose dry eyes and to document any damage to the eye.[1][3]
A Schirmer's test can measure the amount of moisture bathing the eye.[3] This test is useful for determining the severity of the condition.[5] 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.[1] For this test, wetting under 5 mm with or without anesthesia is considered diagnostic for dry eyes.[1]
If the results for the Schirmer's test are abnormal, a Schirmer II test can be performed to measure reflex secretion.[1] 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.[1] For this test, wetting under 15 mm after five minutes is considered abnormal.[1]
A tear breakup time (TBUT) test measures the time it takes for tears to break up in the eye.[5] The tear breakup time can be determined after placing a drop of fluorescein in the cul-de-sac.[1]
A tear protein analysis test measures the lysozyme contained within tears.[1] In tears, lysozyme accounts for approximately 20 to 40 percent of total protein content.[1]
A lactoferrin analysis test provides good correlation with other tests.[1]
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 way diagnose objectively if the samples are indicative of dry eye[10].
Treatment
A variety of approaches can be taken to treatment. These can be summarised as: avoidance of exacerbating factors, tear stimulation and supplementation, increasing tear retention, and eyelid cleansing and treatment of eye inflammation.[11]
General measures
Dry eyes can be exacerbated by smokey environments, dust and air conditioning and by our natural tendency to reduce our blink rate when concentrating. Purposefully blinking, especially during computer use and resting tired eyes are basic steps that can be taken to minimise discomfort.[11] Rubbing one's eyes can irritate them further, so should be avoided [6]. Conditions such as blepharitis can often co-exist[11] and paying particular attention to cleaning the eyelids morning and night with mild shampoos and warm compresses can improve both conditions.
Environmental control
Dry, drafty environments and those with smoke and dust should be avoided.[3] This includes avoiding hair dryers, heaters, air conditioners or fans, especially when these devices are directed toward the eyes.[6] Wearing glasses or directing gaze downward, for example, by lowering computer screens can be helpful to protect the eyes when aggravating environmental factors cannot be avoided [6]. Using a humidifier,[3][4] especially in the winter,[4] can help by adding moisture to the dry indoor air[6].[11].
Rehydration
For mild and moderate cases, supplemental lubrication is the most important part of treatment.[1]
Artificial tears
Application of artificial tears every few hours[3] can provide temporary relief.
Additional options
Lubricating tear ointments can be used during the day, but they generally are used at bedtime due to poor vision after application.[1] They contain white petrolatum, mineral oil, and similar lubricants.[1] They serve as a lubricant and an emollient.[1] Application requires pulling down the eyelid and applying a small amount (0.25 in) inside.[1] Depending on the severity of the condition, it may be applied from every hour to just at bedtime.[1] It should not be used with contact lenses.[1] Specially designed glasses that form a moisture chamber around the eye may be used to create additional humidity.[6]
Fish consumption
Consumption of dark fleshed fish containing dietary omega-3 fatty acids is associated with a decreased incidence of dry eyes syndrome in women.[12] This finding is consistent with postulated biological mechanisms.[12]. Early experimental work on omega-3 eye drops have shown promising results.[13]
Medication
Inflammation occurring in response to tears film hypertonicity can be suppressed by mild topical steroids or with topical immunosuppressants such as cyclosporine.[14][15] Elevated levels of tear NGF can be decreased with 0.1% prednisolone.[1]
Restasis
Topical cyclosporine A (tCSA) 0.05% ophthalmic emulsion is an immunosuppressant, marketed in the United States by Allergan under the trade name Restasis[1]. Approved as a prescription product by the U.S. Food and Drug Administration[5] in 2002, the drug decreases surface inflammation[6]. It is thought to work through inhibition[16] of transcription factors required for cytokine production and T-lymphocyte maturation.[17] In a trial involving 1200 people, Restasis increased tear production in 15% of people, compared to 5% with placebo[5].
Usually, 1 gtt (drop) of Restasis is instilled in each eye twice a day, 12 hours apart.[1] It should not be used while wearing contact lenses,[1] during eye infections [5] or in people with a history of herpes virus infections[6]. Side effects include burning sensation (common)[5], redness, discharge, watery eyes, eye pain, foreign body sensation, itching, stinging, and blurred vision.[1][5] Long term use of cyclosporine at doses over 1000 times greater than that used in the treatment of dry eyes is associated with an increased risk of cancer[18][19].
Conserving tears
There are methods that allow both natural and artificial tears to stay longer.[6]
Blocking tear drainage
In each eye, there are two puncta[21] — little openings that drain tears into the tear ducts[5]. There are methods to partially or completely close the tear ducts.[6] This blocks the flow of tears into the nose, and thus more tears are available to the eyes.[3]
Punctal plugs
Punctal plugs are inserted into the puncta to block tear drainage.[5] For people who have not found dry eye relief with drugs, punctal plugs may help.[5] They are reserved for people with moderate or severe dry eye when other medical treatment has not been adequate.[5]
Cauterization
If punctal plugs are effective, thermal[6] or electric[1] cauterization of puncti can be performed.
In thermal cauterization, a local anesthetic is used, and then a hot wire is applied.[6] This shrinks the drainage area tissues and causes scarring, which closes the tear duct.[6]
Customized contact lenses
Persons with severe dry eyes may benefit from the Boston Scleral Lens which is a customized contact lens.[6] Resting on the sclera, it creates a fluid filled layer over the cornea, thus preventing it from drying.[6]
Surgery
In severe cases of keratoconjunctivitis sicca, tarsorrhaphy may be performed where the eyelids are partially sewn together. This reduces the palpebral fissure (eyelid separation), ideally leading to a reduction in tear evaporation.[3]
Prognosis
Keratoconjunctivitis sicca usually is a chronic problem.[6] Its prognosis shows considerable variance, depending upon the severity of the condition.[1] Most patients have mild-to-moderate cases, and can be treated symptomatically with lubricants.[1] This provides an adequate relief of symptoms.[1]
When dry eyes symptoms are severe, they can interfere with quality of life.[5] People sometimes feel their vision blurs with use,[3] or severe irritation[3] to the point that they have trouble keeping their eyes open[5] or they may not be able to work or drive[5].
Prevention
There is no way to prevent keratoconjunctivitis sicca.
[22]Complications can be prevented by use of wetting and lubricating drops and ointments.
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