Dry Eye

Overview

Eye Cells

Ocular surface

OCULAR SURFACE

The ocular surface is composed of:

  • The free margin of the eyelids
  • The conjunctiva: transparent membrane which lines the inside of the eyelids as well as the sclera.
  • The cornea
  • The lacrimal glands:
    • The principal lacrimal gland (in the upper lid)
    • The Meibomian glands (in the upper and lower lids)
  • The tear film

Eyelids have a function of protection to prevent injury to eyes and a function of tear film maintenance to secrete, distribute and drain.

Blinking performs several essential functions:

  • Ensures tear film is evenly distributed over cornea
  • Blink reflex protects against foreign bodies, removes irritants
  • Normal blinking frequency: 1 blink every 3 to 6 seconds

Tear film

The lacrimal tear is composed of 3 layers that have an essential role for the cornea:

  • Mucin layer: it is composed of mucins which are glycoproteins forming a gel. Mucins are secreted mainly by the mucus cells (goblets) in the conjunctiva. Mucins are hydrophilic and are able to fix the tear film firmly to the cornea and conjunctiva. The mucin layer allows uniform spreading of the aqueous layer over the surface of the cornea.
  • Aqueous layer: the thickest layer of the tear film (90%), it is composed of 98% of water, plus nutrients (glucose) and proteins. It is produced by the principal lacrimal gland and accessory lacrimal glands. It has several functions: protect the ocular surface, hydrate the cornea (water), oxygenate and nourish the cornea.
  • Lipid layer: it is the layer of oil that is composed of triglycerides, cholesterol, waxes. It is secreted by the meibomian glands.It has several functions: to prevent the evaporation of the aqueous layer, to keep the tears in place and to facilitate the blinking.

Tears are secreted by glands located inside eyelids and the conjunctiva (1 to 2 ml/min). Tears are spread by the blinking action of eyelids thus forming the tear film (1 blink every 3 to 6 seconds). The tear film is eliminated throw evaporation and lacrimal pathways

Définition:

Dry eye is a multifactorial pathology that results from tear film damage due to:

  • Either an insufficient production of tears (aqueous deficience form),
  • Either excess evaporation of the tears (evaporative form).

Causes:

Dry Eye is multifactorial and the causes are numerous: 

  • Age: lacrimal glands atrophy resulting in fewer tears. Aggravated by hormonal changes (ex: menopause).
  • Environment: pollution, dry air or air conditioning, cigarette smoke, computer use, smartphone, wind, high altitude
  • Taking medications: antidepressants, analgesics, sleeping pills, antihistamines, anti-acne, anti-diarrhea, hormonal treatments
  • Taking toxic substances: tobacco and cannabis
  • Lasik or cataract surgery or glaucoma
  • Diseases with inflammation of the eyelids (blepharitis): rosacea, seborrheic dermatitis, psoriasis, chronic eye allergies.
  • General diseases: autoimmune diseases: syndrome of Gougerot-Sjögren, rheumatoid arthritis, HIV, hepatitis ...
  • Some Ethnies are more affected: Hispanics and Asians

Physiopathology:

Dry eye can come from different disorders:

  • Tear film disorders (lipid layer, aqueous layer, mucin layer)
  • Corneal surface disorders
  • Blinking mechanism disorders (incomplete blinking or insufficient blinking). Blinking mechanism disorders cause a bad emptying of the Meibomian glands (obstruction and atrophy of these glands).
  • Eyelid disorders

Epidemiology:

Eye dryness affects more than 300 million people worldwide (25% in the USA, 24% in France) (1)

  • The studies show that the prevalence is higher for some people:
    • Elderly people
    • Women
    • Some Ethnies are more affected: the prevalence of severe symptoms is higher among Hispanics and Asians compared to Caucasian
  • Prevalence is increasing due to:
    • our environment and modern life style (pollution, air-conditioning, work on computer …)
    • a better diagnosis due to a better comprehension of the physiopathology

1. SFO 2015 report (French Ophthalmic Society)

Clinical Presentation

Aqueous deficience form

The dry eye aqueous deficience form is an insufficient production of tears. It is a deficiency of the water layer (aqueous) which represents 90% of our tears. This layer is secreted by the principal lacrimal gland.

Evaporative form

Evaporative form

Evaporative dry eye form (75% of cases) is an excess evaporation of tears. It is a deficiency of the oil layer (lipid) that protects against the evaporation of the tear. This layer is secreted by the Meibomian glands.

Symptoms

The symptoms are numerous:

  • Tingling, itching
  • Burning sensation, sand or foreign body in the eyes
  • Sensitivity to light, wind or tobacco smoke
  • Difficulties to open the eyes in the morning, feeling of eyelids stuck
  • Absence of tears in situations known to trigger their secretion (during emotion, peeling onions...)
  • Difficulty wearing contact lenses
  • Impression of a decrease in visual acuity

But dry eye can be asymptomatic.

DryEye

Diagnostic

World Cells

Current solutions for diagnosing dry eye are numerous:

  • Patient history
  • Physical Examination
  • Speed or OSDI Questionnaire
  • Ophthalmic Tests: these tests are numerous. Here is a non-exhaustive list of existing ophthalmological tests:
    • Schirmer test: to measure tear secretion using a filter paper of 5-millimeter graduated placed under the lower lid for 5 minutes, avoiding corneal contact. The length of paper moistened by the tear allows to quantify the tear secretion - normal eye > 15 mm / dry eye <15 mm (hyposecretion)
    • BUT (Break Up Time): Tear film rupture time to assess the tear film stability on the cornea. After instillation of a drop of fluorescein, the patient is asked not to blink in order to observe the time that elapses before the rupture of the tear film - normal eye > 15 seconds / dry eye <15 seconds
    • Ocular staining (fluorescein, lissamine green, rose Bengal): is used to assess the degree of corneal damage and to evaluate the quality of the tear film. It distinguishes a normal cell from a damaged or dead cell. Fluorescein is taken up by no damaged cells in epithelium, staining them in green. The more important the staining, the more the dry eye syndrome is important.
    • Conjunctival impression cytology to assess the integrity of conjunctival surface through sampling epithelial cells collected by means of a tiny filter. Cellular morphology analysis and mucous cell count reveal lesions.

Some new non-invasive imaging tests emerge to complete the arsenal of diagnostic tools for dry eye:

  • Interferometry: is an examination to evaluate the thickness of the lipid layer of the tear film between blinking. The color & structure of the lipid layer (colored fringes like an oil stain) makes it possible to evaluate the quality and the thickness of the lipid layer. This test is very useful for diagnosing Meibomian gland dysfunction (tear film evaporation).
  • Measure of the tear meniscus-height: Evaluation of the tear film quantity (along the lower eyelid margin). The absence of a tear meniscus is an indication of a dry eye. The normal tear meniscus is 0.5 mm between the lower eyelid and the bulbar conjunctiva.
  • NIBUT (Non-Invasive Break Up Time): Non-invasive tear film rupture time is an examination to evaluate the stability of the tear film on the cornea. From blinks, we evaluate the time to the film to break by projecting a grid on the cornea - normal NIBUT between 10 and 15 seconds / Eye dry <10/15 seconds
  • Meibography: a non-contact infrared system for a quick and easy way to obtain an overall image of the morphology of the Meibomian glands (which produce the lipid layer). Meibography allows the evaluation of the Meibomian glands loss, atrophy and obstruction.

Some new biologic tests emerge to complete the arsenal of diagnostic tools for dry eye:

  • Lacrimal osmolarity: to evaluate the salinity of the tears. The lacrimal hyperosmolarity is an indicator of dry eye. It can serve as a diagnostic and quantitative evaluation of the severity of dry eye, especially for early and asymptomatic cases - moderate to severe dry eye> 312 mOsmoles / liter
  • MMP-9 Test is the quantification in the tears of the MMP-9 (a cytokine produced by epithelial cells) allowing the diagnosis of the ocular surface inflammation. These enzymes, which normally participate to tissue remodeling, are more important in the tears in case of ocular surface inflammation. Dry eye: MMP-9 is > 40 ng / ml.

Treatment

Eye Cells
  • Hygiene of the eyelids
  • Lacrimal substitutes (tears and gel)
  • Lubricating eye drops
  • Scleral lenses

Goutte

  • Eyelids heating (eg heating masks and goggles)
  • Mechanical palpebral massage

These therapeutic solutions have an effect on the Meibomian glands dysfunction (deficiency of the lipid layer). These solutions make it possible to liquefy the meibum, to drain the Meibomian glands and to prevent them from becoming clogged and atrophied.

  • Mechanism of action: An IPL system is a polychromatic pulsed light generator that emits a train pf pulses of light stimulating and accelerating the metabolism of the lacrimal glands
  • Sessions: the practitioner applies to the patient some eye protective goggles and applies 4 to 5 shots of light under each eyelid (under the lower eyelid to the outer canthus). The treatment is fast and painless. The treatment requires 3 to 4 sessions spaced between 2 weeks to 1 month.
  • Clinical effects: IPL treatment improves the quality of the tear film and the symptoms felt by the patient are significantly improved. Others clinical improvements are also observed: analgesic, anti-inflammatory (blepharitis, conjunctivitis), antimicrobial (bacteria and Demodex infection), stimulation and tissue regeneration.

References

Cells

 

  1. TFOS DEWS II 2017
  2. SFO 2015 Report (French Ophthalmic Society)
  3. Comment diagnostiquer et suivre une sécheresse oculaire? A. Rousseau, M. Labetoulle Service d’Ophtalmologie, Hôpital de Bicêtre, Université Paris-Sud, LE KREMLIN-BICÊTRE. Réalités Ophtalmologiques, Juin 2012
  4. Yeux secs – Diagnostic - Quoi de neuf ? Docteur Jean-Pierre Lagacé, optométriste, M.Sc. OPTOMETRISTE, Juin 2016
  5. Exploration de la sécheresse oculaire - G. Vandermeer, PJ Pisella, CHRU Bretonneau, Tours. Réalités Ophtalmologiques, Janvier 2017
  6. Diagnostic et traitement de la sécheresse oculaire: de nouveaux outils pour la pratique quotidienne - A. ROUSSEAU, M. LABETOULLE, Service d’Ophtalmologie, Hôpital de Bicêtre, LE KREMLIN-BICÊTRE. Réalités Ophtalmologiques, Mai 2017
  7. Dysfonctionnement meibomien : du diagnostic au traitement - G. CASSE, Clinique PASTEUR, Atrium Vision, Atrium LASER, TOULOUSE. Réalités Ophtalmologiques, Décembre 2017
  8. Sécheresse oculaire et chirurgie de la cataracte - A. ROUSSEAU, M. LABETOULLE, Service d’Ophtalmologie, Hôpital de Bicêtre, LE KREMLIN-BICÊTRE. Réflexions Ophtalmologiques, Février 2018
  9. Prospective Trial of Intense Pulsed Light for the Treatment of Meibomian Gland Dysfunction - Jennifer P. Craig, Yen-Heng Chen, and Philip R. K. Turnbull. The Association for Research in Vision and Ophthalmology, Inc. www.iovs.org, 2015
  10. Evaluation of the Safety and Effectiveness of Intense Pulsed Light in the Treatment of Meibomian Gland Dysfunction - Xiaodan Jiang, Huibin Lv, Hang Song, Mingzhou Zhang, Yan Liu, Xiaodan Hu, Xuemin Li, and Wei Wang. Hindawi Publishing Corporation. Journal of Ophthalmology, 2016
  11. Intense Pulsed Light for Dry Eye Disease - Rolando Toyos, MD. Glaucoma Today, Juillet 2016
  12. Analysis of Cytokine Levels in Tears and Clinical Correlations After Intense Pulsed Light Treating Meibomian Gland Dysfunction - Ruixing Liu, Bei Rong, Ping Tu, Yun Tang, Wenjing Song, Rolando Toyos, Melissa Toyos, and Xiaoming Yan. American journal of ophthalmology