in

DRY EYE MECHANISMS

DRY EYE MECHANISMS

The diagnosis of dry eye is complicated due to the significant inconsistency between the symptoms reported by the individual and the signs observed. This inconsistency can be explained by the variability of the tests used for this condition, the variability of the disease process, the subjectivity of the symptoms, individual variability of the pain threshold, and the cognitive responses to questions about visual sensitivity. 3

Risk factors were classified in the TFOS DEWS II as consistent, probable, and inconclusive. Age, gender, ethnicity, meibomian gland dysfunction (MGD), Sjögren’s syndrome, androgen deficiency, computer use, contact lens wear, hormone replacement therapy, hematopoietic stem cell transplantation, some environmental factors (places with low humidity, pollution), and systemic medications (antihistamines, antidepressants, anxiolytics, and isotretinoin) were identified as consistent factors.1

DRY EYE AND SYSTEMIC DRUGS

In the United States, four out of every five adults use drugs prescribed by their doctor, over-the-counter drugs, or nutritional supplements in a week.3,4 Because the use of drugs and herbal products is more common in the geriatric population. Due to the higher prevalence of chronic degenerative diseases, knowledge of these specific products is important since they play a vital role in the eye health of these cases.3-5

According to the iatrogenic dry eye classification, systemic drugs were classified in section 1A (induced by systemic drugs). Among the 100 best-selling drugs in the United States, at least 22 cause dry eye; of the nine drugs known to have tear concentrations, eight cause dry eye. Most studies looking at drug-induced dry eye only include drug families and not individually.6

The mechanisms by which an iatrogenic dry eye secondary to drugs can be generated are the following: decrease in tear production, alteration in the afferent nerves and reflex secretion, inflammatory effects in the glands, or direct toxicity through the tear. 62% of dry eye cases in elderly patients have been related to some systemic medication, especially: non-steroidal anti-inflammatory drugs (NSAIDs; OR 1.30), diuretics (eg: furosemide, OR 1.25), vasodilators ( OR 1.37), analgesics / antipyretics (OR 1.28), gastric protective drugs (eg, ranitidine, OR 1.44), sulfonylureas (OR 1.3), cardiac glycosides (OR 1.28), beta-blockers (eg, propanolol), anxiolytics / Benzodiazepines (eg, lorazepam, OR 2.35), antimicrobials (OR 1.88), antidepressants / antipsychotics (eg, amitriptyline, thioridazine, OR 2.54), anticonvulsants (eg, valproic acid), hypotensives (eg: candesartan, OR 1.98), inhaled steroids (OR 2.04), systemic steroids (OR 1.60), oral contraceptives, hormone replacement therapy (OR 1.60), drugs for benign prostatic hyperplasia (OR 1.35), multivitamins (OR 1.41), decongestants ( e.g. pseudoephedrine), drugs for the treatment of Parkinson’s disease (e.g. j: trihexyphenidyl), some herbal supplements (eg. eg: echinacea, niacin and kava) and antihistamines (eg: cetirizine, OR 1.67) .2,3,6 Table 1 shows the main families of drugs involved with the pathogenesis of dry eye and some examples.

DRY EYE MECHANISMS

A group of drugs that can cause dry eye are those with anticholinergic activity, specifically those associated with protein G; these can affect the acini of the lacrimal gland and the mucus-producing cells, which reduces the watery mucinous component and alters the tear stability. As a peripheral effect, antihistamines can cause dryness in the oral and respiratory mucosa.2 Likewise, cholinergic receptors have been identified in the epithelial cells of the meibomian glands, possibly affecting tear quality in this component. In addition, adrenergic drugs (beta-blockers and alpha-agonists) alter both tear production and quality; this mechanism is believed to be secondary to protein kinase C production and intracellular calcium concentration.6 Beta-blockers reduce levels of lysozyme and immunoglobulin A, in addition to this, can cause corneal anesthesia and a decrease in tear rupture time (TRL) .2

The four non-steroidal anti-inflammatory drugs (NSAIDs) most associated with the development of dry eye are ibuprofen, ketoprofen, diclofenac, and acetylsalicylic acid, latter reaching significant concentrations in tears and causing dry eye and superficial punctate keratitis.2 Ketoprofen rarely causes dry eye per se, but it does have the potential to aggravate pre-existing symptoms.

Some chemotherapeutic agents such as methotrexate, mitomycin C and busulfan have been shown to cause alterations in tear quality and reflex secretion.6

Excess retinoic acid causes blepharitis and dry eye; the proposed mechanism is atrophy of the meibomian glands and later alteration in lipid secretion.

Isotretinoin prevents the proper function of the meibomian glands, increasing tear evaporation.3

Antidepressants have a similar chemical structure to atropine, an anticholinergic agent with well-known antimuscarinic effects. The antagonistic effect of antidepressants on muscarinic receptors causes dry eye by affecting smooth muscle and glandular tissue.7

Anticonvulsants, by having an anticholinergic effect, block the effect of the neurotransmitter acetylcholine. Some specific agents that have been reported are phenobarbital, primidone, valproic acid, and lamotrigine.8
It is one of the most frequent causes for which a patient goes to an ophthalmological consultation.

It is an entity of multifactorial causes, which produce as a common denominator the alteration of the composition of the tear film and, therefore, the ocular surface.

Although it is a benign pathology, its importance lies in its chronicity since it does not have a definitive cure and in the significant alteration of ocular well-being that it produces.

To better understand the varied symptoms that it can produce, we must explain the functions of the tear film, which bathes our eyes. In addition to its nourishing and protective function, it has a cleaning function and an optical function.

CAUSES OF DRY EYE SYNDROME

         Long-term use of contact lenses.
         Use of display screens.
         Aging. It is more frequent the older.
         Systemic diseases such as allergy, diabetes, rosacea, Parkinson's, Sjögren, atopy.
         Accidental or surgical eye trauma (post-operated cataract and Lasik)
         Facial paralysis
         Hormonal changes, especially those of menopause and hypothyroidism.
         Positional alterations of the eyelids, such as drooping lower eyelids in senile patients.
         Drugs, especially topical medications used to treat glaucoma and oral contraceptives. It is also frequent in the use of antihypertensives, antipsychotics, antihistamines, estrogens, and retinoids.
         Physical environmental factors such as hot and dry environments, convection currents, and air conditioners. Other types, pollution, tobacco, and alcohol.

In all symptomatic cases, there is an increase in the loss of ocular moisture due to tear evaporation, which leads to instability of the tear film, which leads to inflammation of the eye’s surface, which can lead to injuries. Corneal.

SYMPTOMS OF DRY EYE SYNDROME

The most common symptom is the sensation of sand or foreign bodies in the eyes and the redness of the eye. There may also be excessive tearing as an ocular defense mechanism against dryness.

The fluctuating vision in the reading is very frequent due to the irregularities of the corneal surface present in dry eyes. Characteristically, vision improves with blinking in these patients.

Patients suffering from blepharitis also complain of burning, burning.

Patients with allergies mainly complain of itching.

Pain may be present in cases of severe dry eye.

Photophobia (hypersensitivity to light) is present in moderate/severe dry eye cases since it is due to corneal erosions secondary to dryness.

The discomfort may be absent in patients undergoing refractive surgery, masked by corneal anesthesia in the first postoperative weeks.

A characteristic aspect of dry eye symptoms is the lack of correlation between the signs found in the examination with the symptoms reported by the patient. Very symptomatic pictures may not have special alterations on examination and vice versa.

What do you think?

Written by starinky

Leave a Reply

Your email address will not be published. Required fields are marked *

GIPHY App Key not set. Please check settings

Symptoms and signs of dry eye

Symptoms and signs of dry eye

TREATMENT OF DRY EYE SYNDROME

TREATMENT OF DRY EYE SYNDROME