Evaporative Dry Eye
As we mentioned before, there are two main causes of dry eyes. The first is deficiency of tear film production and the second cause is evaporation of tear film. In Evaporative dry eye there is excessive evaporation of tears and this cause is the main cause of dry eye. The most common causes of evaporative dry eyes are:
1- Meibomian Gland Dysfunction ( MGD)
It is the most common cause of dry eye. Meibomian glands or tarsal glands are small oil glands that open on the eyelid margin. There are 30-40 meibomian glands on the upper eyelid and around 20-30 glands on the lower eyelid. These glands secret oil to the corneal surface and this oil covers the aqueous part of tear film and prevent it from evaporation.
Causes of Meibomian Gland Dysfunction
1- Age. The number of these glands decreases with age
2- Ethnic background. It is more common in asian population
3- Inflammation of the eyelid margin. Inflammation of the eyelid margin can obstruct the pores of Meibomin glands .There are many causes of inflammation of the eyelid margin such as blepharitis, allergic conjucntivitis,bacterial infection, autoimmune diseases such as acne rosacea, rheumatoid arthritis and Systemic Lupus Erythematosus.
4- Make-up such as eyeliners and mascara can block the pores.
5- Contact lenses wear
6- Medications that affect the production of oil such as estroge replacement therapy and retinoid that can be used to treat acne
7- Destruction to meibomian glands such as infections cnjucntival scars, trauma and chemical burns to eyelid
Symptoms of MGD
It is similar to symptoms of dry eyes and blepharitis
Diagnosis of Meibomian Glands Dysfunction
Your eye doctor can detect it during routine eye examination with slit lamp. He will look to the sturcture of the eyelid margin and also to the pores or opening of the glands. Gentle pressure on the eyelid margin to see the secretion. A new handheld instrument called meibomian glands evaluator can be used by your eye doctor to evaulate the secretion of these glands and also to grade the severity of dysfunction
Treatment of Meibomian Glands Dysfunction
It is very important to treat the underlying cause of it
1- Antibiotics and steroid. Used to treat blepharitis and associated infection and inflammation. Tetracycline can be used as oral medication to treat MGD. It has both antibacterial and ani inflammatory properties.
2- Meibomian glands probing. This technique helps to open the pores of the gland and it can be very helpful and many people feel improvement in symptoms after that. This technique is performed by your eye doctor in the clinic.
3- Warm compressor and massage to the eyelid and eyelid margin with washing of the eyelid margin can be very helpful for that.
4- Omega 3 fatty acid can enhance the quality and the quantity of oil secreation from these glands. Omega 3 fatty acid also has anti inflammtory function.
5- LipiFlow Thermal Pulsation System. It is a device that can be used by your eye doctor in outpatient clinic to treat Meibomian gland dysfuction in 12 minutes session. It use both heat and pulse. Heat to melt the oil secretion and pulse to push the secretion out of the gland
2- Exposure of Ocular Surface
1- Defects in the closure of the eyelids that can be due to mechanical or neurological factors. Severe dry eyes can occur from chronic corneal exposure to the atmosphere
Mechanical causes can be due to eyelid trauma, after surgical procedures or there is abnormality in the position of the globe such as proptosis or abnormal protrustion of the globe
Neurological causes lead to poor blinking reflex which is normally about 15 blinking per minutes. It can be caused by stokes and Bells palsy or facial nerve palsy.
2- Abnormal lid-globe congruity with either entropion (in-turning of the lids toward the globe) or ectropion (out-turning of the lids from the globe) leading to more exposure of ocular surface to atmosphere and more evaporation of tear films.
3- Reduction in blink rate. Blink reflex is very important to reduce evaporation of tear film. When you work on computer, mobile or ipad, you blink less frequently than normal which cause more evaporation of tear. Also jobs that require visual concentration for a long time such as driving, reading and watching TV for along period
3- Environmental Factors
Such as sun, hot climate with lower humidity, wind and dry air that commonly occurs in the cabins of airplanes. Air conditioned room with low humidity
4- Contact Lenses and Dry Eye
Wearing them for a long time can increase the evaporation rate of tear and also decrease the rate flow of tears.