. . . that makes everything easier to understand
GRITTY EYES - DRY EYES - WATERING EYES - ITCHY EYES - EYE REDNESS - OBSTRUCTED GLANDS - TIRED EYES - HEAVY LIDS - BLURRED VISION - UNSTABLE VISUAL ACUITY ... AND MANY MORE ..
All these different and partly contradictory appearing complaints ... can be symptoms of an EYE IRRITATION that occurs due to a DAMAGE of the Ocular Surface TISSUE.
This happens typically following a DEFICIENCY of the TEAR FILM in front of the eye. It can then no longer keep the delicate tissue sufficiently moist ... with the consequence that the Tissue DRIES OUT - This is the reason behind the term "DRY EYE"
The so-called ´DRY´ EYE DISEASE is a very wide-spread condition and represents the most frequent diagnosis in clinical practice.
In contrast to the term "Dry" the occurring irritation of the ocular surface tissue may also lead to episodes of excessive tearing and watering eyes. This occurs particularly in the initial stage of this condition and is often difficult to understand for the patient.
DOCTOR, MY EYES ARE WATERY ... HOW CAN THAT BE ´DRY EYE´ DISEASE ???
The increased tear flow in case of watering eyes indicates a (still) intact protective tearing reflex.
This reflex is generally triggered by irritation of many kinds such as e.g. wind and fans, or foreign bodies etc.
Such irritating incidences make the tears flow to remove the stimulus.
When the damage to the ocular surface proceeds, this protective reflex will unluckily also become dysfunctional and disappears.
DRY EYE DISEASE can be a ´tricky´ condition of the Ocular Surface
These few contemplations already indicate, that the so-called ´DRY EYE´ Disease can be an unexpectedly tricky issue.
´Tricky´ is not only the fact, that an eye in ´Dry Eye Disease´ can be watering.
Tricky is also the fact that... surprisingly ... most patients with ´Dry´ Eye Disease do not have a primary lack of water but they have a primary lack of oil in the tear film. The oil has the function to slow down the evaporation of tear water.
The healthy function of the Ocular Surface depends on a large number of factors that are inter-related and inter-dependent.
The functional and structural network at the Ocular Surface may probably be compared to a house of cards - it appears stable ... but as soon as only one card is moved ...
Science is working on the resolution of this disease for quite a while and has made considerable advancements of knowledge.
This has translated into benefit for the daily lives of hundreds of millions of patients world-wide who suffer from DRY EYE DISEASE.
But even deeper insight into the disease process and thus continued scientific advancements are necessary to offer more effective strategies for therapy in the future.
IMPORTANT for the patient is to UNDERSTAND his/her CONDITION ... in order to understand the many ways to influence the condition in a beneficial way.
IF you are interested in more stunning news from the ocular surface ... you are IN THE RIGHT PLACE ... HERE ...
... at the INFORMATION PLATFORM on the OCULAR SURFACE and DRY EYE DISEASE of the OCULAR SURFACE CENTER BERLIN (OSCB)- A non-profit Science Institute for the advancement of knowledge on the Ocular Surface and Dry Eye Disease that is set up and run by experienced scientists in the field..
The Ocular Surface
The OCULAR SURFACE ... is the moist anterior part of the eye
The shining of the Ocular Surface comes from the Tear Film
that maintains the permanent Moisture of the Ocular Surface.
The OCULAR SURFACE performs the first steps of VISION
The OCULAR SURFACE is that part of the eye that permits the entrance of Light.
Only after passing the Ocular Surface
... can this light elicit responses of the Retina in the back of the eye
... that later allow the ´curious´ Brain to construct an image of the outside world on the screen of consciousness.
Without a healthy and functioning Ocular Surface, all other steps of the Vision Process that happen later and further ´behind´ ... are basically meaningless.
The OCULAR SURFACE must be permanently MOIST
Our Ocular Surface has the biological requirement that it must be permanently moist - ´always and everywhere´ - to keep the transparent window of the cornea indeed clear.
The Moisture is produced by the associated Glands of the Ocular Surface and it is termed as the ´Tears´ *.
Since we are living in a dry environment with an air atmosphere, it is actually quite laborious to preserve this little artificial moist ´ecological niche´ of the Ocular Surface - ´always and everywhere´ !
PS: * except for moistening the Ocular Surface, Tears are also of use to give the emotional signal to our fellow human beings that we are exceptionally sad ... or probably exceptionally happy by shedding ´tears of joy´
Opening the eye lids for the entrance of light ... puts the Ocular Surface in some kind of a DILEMMA
The requirement of Moisture - ´always and everywhere´ - confronts the ocular surface with a problem or, more positively thinking, this gives it the change to deal with a Challenge:
Light can only enter the eye when the eyelids are opened ...
... on the other hand, opening of the eyelids would at the same time immediately deprive the Ocular Surface tissue of its moisture and it would start to dry out.
To solve this Dilemma, the Ocular Surface has to apply a ´Trick´: A very narrow layer of fluid is formed from the tears - this is for obvious reasons termed as the Tear Film.
The Tear Film is thick enough to preserve the moisture for the underlying cells of the tissue but not too thick in order not to harm the transmission of light.
The Ocular Surface in fact manages to be even more ingenious, because it solves the dilemma by even improving the passage of light through the presence of the Tear Film. The Tear Film fills in all subtle inequalities of the surface and thereby provides a perfectly Smooth Surface layer for perfect refraction of the incoming light that allows for perfect Visual Acuity.
The TEAR FILM is the SOLUTION for all requirements of the Ocular Surface ... and for VISION
The Tears are transformed into the thin, homogeneous Tear Film through the coordinated Blink Movement of the Eye Lids.
During the Blink mainly the upper eye lid wipes over the anterior surface of the eyeball and thus distributes the tears into the Tear Film.
Only through the coordinated blink movement of the eyelids, together with the very special composition of the Tear Film, is it possible to form a Film that is extremely thin (only about one hundreds of a millimeter).
At the same time this very narrow tear film must still be stable to allow the curious brain to achieve a sufficiently sharply focused image of the outside world.
The Tear Film must be stable for at least 10 seconds on average until it eventually breaks up and triggers a stimulus that induces a new blink that forms a new tear film.
Having said this ... all major things are basically named ... The basic functional pre-condition at the ocular surface for vision is a Stable Tear Film. This is achieved by the Basic Functional Complexes of Tear Secretion/ Production by the ocular glands and of the physical Tear Film Formation by the blink movement of the eyelids.
Dry Eye Disease
Because the formation and preservation of the Tear Film is very laborious in the dry environment that we live in, it is very failure-prone.
The Tear Film is influenced by a multitude of very different Influence Factors and Risk-Factors, that can, in one or the other way, have a negative influence on it.
ALL these negative factors can, sooner or later, lead to a Dry Eye condition. The large number of influence factors that may appear unrelated at first glance can let Dry Eye Disease appear as a ´Tricky Condition´ - even though it basically straightforward.
The fact that the Tear Film is there to prevent Drying of the Ocular Surface Tissue indicates that typically the most immediate consequence of a Dry Eye condition is the Drying and thus Destruction of the Ocular Surface Tissue.
This results in a ´downstream´ irritation of nerve fibers that transmit ocular irritation of various degrees probably leading to a chronic pain syndrome, and inflammatory reactions that can reinforce the whole process.
Since the Tear Film also has an important function for the refraction of light and thus for the provision of visual acuity, it is no surprise, that visual disturbance is frequently reported in Dry Eye Disease, typically in terms of unstable visual acuity and blurred vision
Some Ideas for THERAPY in Dry Eye Disease
What can be done as a THERAPY for Dry Eye Disease ?
In most cases there is a deficiency of the Tear FILM based on a qualitative or quantitative lack of Tear Components.
Therefore TEAR SUPPLEMENTATION, i.e. the addition of missing tear components - in the form of eye drops or of a spray - is the most frequently used therapy option.
Sometimes this is termed Tear ´Replacement´ - but, since the (full) Tears with all ingredients can (unluckily) not be replaced at present and in the foreseeable future, the term ´Supplementation´ appears more appropriate.
All different sorts of eye drops based on aqueous solutions with a lot of different additional ingredients are available, mostly as prescription free over the counter products.
A lack of OIL is the main starting point for Dry Eye in most patients with Dry Eye Symptoms
According to the present scientific knowledge, the vast majority, i.e. four of five patients with a Dry Eye Condition, does NOT have a primary lack of water but instead a PRIMARY LACK OF OIL in the tear film.
This leads to increased water evaporation and decreased tear film stability .... with a secondary water loss.
Therefore, in most patients, it does not seem to make much sense nowadays to use products that do not contain lipids in one or the other way.
It may be possible to replace the effect of lipids on the tear film by other compounds, or to simply use lipids only, e.g. as a liposomal spray. ... In other words, LIPIDS or respective compounds should nowadays be a component of typical Tear Supplementation Products.
The lack of oil is typically due to a Dysfunction of the Meibomian Glands inside the Eyelids.
The lack of oil on the ocular surface is typically due to Meibomian Gland Dysfunction (MGD), a mostly obstructive condition of the Oil-producing little glands inside the eye lids. They are blocked by inspissated secretum and excessive keratinization.
Rare blinking of the eyelids, that helps to express the oil from the glands, is another important factor for a lack of oil on the tear film.
PHYSICAL THERAPY helps to restore the function of the Meibomian glands in the Eyelids ... and thus improves Dry Eye Disease
PHYSICAL THERAPY options refer to the fact that the improvement of Eyelid and Meibomian Gland Disease is based on simple but effective physical techniques such as Warming and Moistening, as well as manual Massage and Expression of the Glands with subsequent Scrubbing and Cleaning of the Eyelid Margin.
It is certainly important to note that before any manipulations are done to the eyelids and the eye a clinician should always be consulted for an educated diagnosis and for therapeutic recommendations before any therapy measures are applied to the eye and eyelids !
Physical Therapy should be done as a permanent therapy, at best twice a day, because a chronic disease typically requires a chronic therapy !
Physical Therapy consists of 3 Steps
(1) WARMING of the Eyelids
- WARMING, preferably together with moisture
- for at least 10 minutes
- to reach a temperature of 40°C inside the eyelid and thus within the Meibomian Glands
- serves to re-liquefy the inspissated oil inside the Meibomian glands.
In order to achieve 40°C inside the eyelid a slightly warmer (42-45°C) moist warm compress/ cloth must be rewarmed (e.g. from a larger bowl of hot water) every two minutes as shown by studies.
The additional moisture serves to soften up the cornified epithelial squames and lipid encrustations on the eyelid margin.
Commercially available gel masks of even electrically heated and moistened googles may make the potentially laborious effort of physical therapy, twice a day, considerably easier ...
(2) Subsequent Lid MASSAGE to EXPRESS and relieve the obstructed glands
- when the inspissated oil that is stuck inside the Meibomian is sufficiently warmed it will become more liquid again
- a careful eyelid massage can then express the pathologic content from the Meibomian glands onto the lid margin
- massage must always be directed towards the gland orifice on the lid margin, i.e. towards the palpebral fissure (as shown in the animation to the right)
- the upper eyelid is thus massaged downwards
- the lower lid is massaged upwards
- when the oil is very hard and insufficiently re-liquefied it may be necessary to perform a more vigorous expression of the eyelid , e.g. between two fingers (as shown) in the animation to the right
- such procedures can be painful and
- can potentially hurt the eyelids and glands
- during any procedures applied to the eye by a layman it must therefore alway be safeguarded that no harm and wounding is caused to the eye, eyelids and glands !
(3) Eyelid/ Lid Margin HYGIENE concludes physical therapy
- finally, the eyelid margin together with the base of the eyelashes should be cleaned
- from the expressed pathological oil
- from bacteria and bacterial products that occur on every normal lid margin but increase in disease
- from cornified skin squames that deposit on the lid margin
- Lid Margin HYGIENE is done by a soap-free wiping or ´scrubbing´ of the lid with a cotton-tipped rod or a cosmetic pad in order to remove any debris, encrustations and foam from the lid margin.
- it appears important to avoid any soap, shampoo, or any other detergents, as has previously occasionally been recommend., because that would conceivably destroy the tear film lipid layer.
- Oily solutions of any kind appear more suitable for eyelid cleaning.
- Commercial eyelid cleaning kits are available that contain everything necessary in a pre-prepared set and may make eyelid hygiene much easier.
The advantage of such physical therapy options is certainly, that this can mostly be done at home by the patients themselves. It may appear as a disadvantage that physical therapy and in particular lid hygiene has to be done routinely once or twice a day, similar e.g. to tooth brushing, but requires slightly more time.
Please Remember: A Happy Eye Lid typically makes a Happy Dry Eye Patient !
CONTACT LENSES are a fantastic Optical Tool ... customized to the Ocular Surface
Contact Lenses are a fantastic Optical Tool with some clear optical advantages compared with spectacles.
At the same time they provide greater ´freedom´ for outdoor activities, sports and society events.
Contact Lenses are, as their name indicates, in direct ´contact´ with the Ocular Surface.
Contact Lenses are in fact sitting in the middle of the Ocular Surface Functional Unit - with potential influence on all tissues and on the tear film. Contact Lenses thus have a somewhat ambiguous role for the Ocular Surface - with Pros and Cons.
Contact Lenses are swimming on the Eye ... and thus have higher requirements for the Tear Film
Contact Lenses can be used for medical purposes such as the optical correction of an irregular corneal shape or for the protection of the eye e.g. in severe cases of Dry Eye Disease.
On the other hand, Contact Lenses have higher ´requirements´ for the amount and/or quality of the tear film.
It may well be, that an individual with a borderline normal tear film, who is still without symptoms, may develop Dry Eye symptoms upon insertion of an ordinary soft hydrogel contact lens. A typical side effect of Contact Lenses is therefore the onset of Dry Eye symptoms and eventually probably of Dry Eye Disease.
On the other hand an individual with a severe Dry Eye Disease may profit from the application of a special so-called ´Scleral´ Contact Lens that is able to preserve the tear solution underneath the contact lens and in front of the cornea.
HYGIENE is a CRITICAL ISSUE in Contact Lens Wear
Contact Lenses have seen great improvements in the past decades.
This has lead to a reduction in the frequency and severity of side effects.
Insufficient Hygiene can lead to serious and sight-threatening infections in contact lens wear.
This is still an important issue, particularly for inexperienced wearers.
Due to the increasing use of disposable contact lenses for short term wear, particularly daily disposables, the risk of infection can be reduced.
Please find more information below on => Contact Lenses and the Ocular Surface
... Function of The OCULAR SURFACE & some Details on DRY EYE DISEASE
of the Ocular Surface
The Ocular Surface is a permanently MOIST TISSUE
The OCULAR SURFACE is the moist tissue at the anterior side of the eye ball
Moisture is necessary to preserve its health and integrity - and it is thus a pre-requisite for VISION.
[ EVERY SENTENCE OF THIS SHORT SUMMARY IS LINKED TO A RESPECTIVE CHAPTER OF THE DEEPER INSIGHT BELOW, THAT EXPLAINS THE CONTEXT IN MORE DETAIL AND ILLUSTRATES IT WITH EASY TO UNDERSTAND IMAGES ]
MOISTURE comes from the Tears, is produced by the Ocular Glands ... but must be spread into a Tear FILM by the BLINK Movement of the Eye Lids ... to make moisture PERMANENT - Everytime and Everywhere !
Basic Functional Complexes of the Ocular Surface
The Glands of the Ocular Surface produce the TEARS and they are the essential medium for the provision of moisture at the Ocular Surface.
The TEAR FILM makes it possible that moisture can even persist on the tissue within the opened palpebral fissure. and aids in allowing a perfect vision at the same time.
The EYE LIDS spread the tears into the essential pre-ocular Tear Film.
The Healthy OCULAR SURFACE is a Pre-Requisite for Vision and without it all later steps of the vision process are meaningless.
for Dry Eye Disease
DRY EYE DISEASE is a ´dog of many names´
DRY EYE DISEASE is medically also addressed as ´Keratoconjunctivitis Sicca´ - which means ´dry inflammation of the cornea and conjunctiva´ or only as the ´Sicca Syndrome´ (bunch of symptoms related to dryness) . This condition has various colloquial names such as simply ´dry´ eyes, ´ocular dryness´, ´itchy eyes´´heavy lids´ or ´tired eyes´ etc.
The Disease MECHANISM is relatively simple and therefore this condition is relatively frequent
DRY EYE DISEASE IS AN ALTERATION OF THE TEAR FILM AND TISSUE
Dry Eye Disease typically shows the two PATHOLOGIES of
- Tear FILM Deficiency with an unstable tear film that shows e.g. early break-up, increased evaporation, low tear meniscus.
- A deficient, unstable tear fluid layer can no longer protect the surface tissue. Therefore the very susceptible surface cells will then immediately start to develop drying alterations that damage the tissue. Therefore, a subsequent DAMAGE of the ocular surface tissue is the typical result of Tear Film Deficiency.
THE BASIC CAUSATIVE FACTORS FOR DRY EYE DISEASE ARE A LACK OF TEAR SECRETION AND OF FILM FORMATION
The basic CAUSATIVE FACTORS for Dry Eye Disease are those that directly lead to the deficiency of the Tear FILM - this is
- a quantitative or qualitative LACK/ Deficiency of TEAR secretion by the Glands
- and/ or
- ANY Deficiency that negatively influences BLINK MECHANISM of the Eye Lids which distributes the Tears into the pre-ocular
The pathology of Dry Eye Disease gives rise to a number of different subjective SYMPTOMS and clinical SIGNS
Tear Film Deficiency and Surface Damage lead to typical subjective irritative SYMPTOMS of the patient. These are, e.g. ocular dryness and grittiness, often described as ´heavy eye lids´ or ´tired eyes´, together with an unstable visual acuity and episodes of blurred vision, with various degrees of irritation and pain.
Typical clinical SIGNS of Dry Eye Disease are a lack of tear volume on the ocular surface, a lack of tear production, and a short stability of the tear film. This leads to a lack of the essential permanent moisture and thus to different forms of recognizable damage, redness and inflammation of the surface tissue including the lid margin and the ocular glands.
Frequent RISK FACTORS
for DRY EYE DISEASE ... and their Self-Perpetuating INTERACTION
A certain CHALLENGE in the understanding of Dry Eye Disease is based on the fact, that it can be initiated and influenced by a large variety of different factors
- REGULATORY SYSTEMS of the body such as the nerve system, the endocrine hormonal system and the immune system have great importance.
- There are additional RISK FACTORS, that have a negative influence on the tear fluid or on the ocular surface tissue and thus increase the likeliness for the onset and progression of disease.
Unluckily, Dry Eye Disease has a certain inherent tendency to self-enforce and perpetuate itself, if not timely diagnosis and effective therapy is performed
The complex pathologic events in Dry Eye Disease tend to influence each other negatively and thus form self enforcing VICIOUS CIRCLES of Disease Progression.
This does often lead to a worsening of disease without a timely diagnosis and an effective therapy.
An occasional ´Dry´ Eye condition can certainly happen also in healthy individuals under certain conditions - however, when this becomes chronic, it can develop into a disease
Occasional ocular DRYNESS can certainly occur once in a while also in healthy individuals. Such dryness typically depends on adverse environmental factors, is short-lived and disappears quickly after some vigorous eye blinks or when the negative factors are removed. When the condition becomes chronic, however, an occasional ocular dryness can turn into a manifest permanent Dry Eye DISEASE.
CONTACT LENSES and the Ocular Surface
CONTACT LENSES are a fantastic Optical Tool - with pros and cons
Contact Lenses are a fantastic Optical Tool that has long been desired by many individuals with refractive disorders.
They became eventually widely usable only in the second half of the 20th century and have seen great.improvements since then.
CONTACT LENSES correct refraction directly on the Cornea ... with clear optical advantages
Contact Lenses can correct refractive errors directly on the cornea and therefore, they have some principal optical advantages compared to spectacles.
Contact Lenses certainly provide greater ´freedom´ for the user in a lot of sporting, outdoor and society activities.
There are different basic types of Contact Lenses. Soft hydrogel Contact Lenses are the most widely used type.
Soft lenses can typically be worn without distinct irritation and thus often require no adaptation time for the wearer to get used to a lens.
This may be a reason why most Contact Lenses are of the ´Soft´ type and are not worn for medical but for esthetic/ cosmetic reasons.
CONTACT LENSES are swimming in the Tear Film and have influence on its stability and evaporation rate
The fact that Contact Lenses are sitting in the middle of the Ocular Surface has some pros and cons.
They certainly have some clear optical advantages ...
... but contact lenses still represent a ´foreign body´ for the Ocular Surface Tissues and Tear Film.
Even though contact lenses are typically ´swimming´ in the tear film it is still inevitable, that they are in mechanical contact with the ocular surface tissues.
A typical side effect of contact lenses therefore is the occurrence of increased frictional forces to the ocular surface tissues.
CONTACT LENSES can have negative influence on the Ocular Surface Fine Structure
Although fitting principles usually try to avoid too much physical ´touch´, contact lenses are still, inevitably, in contact with the ocular surface - just as their name suggests.
Contact lenses can thus have mechanical, physicochemical and chemical impacts on the Ocular Surface to varying degrees
This concerns particularly the interference of the contact lens with the very sensitive central cornea and the similarly sensitive posterior lid border.
The conjunctival areas on the eyeball and on the back side of the lids are less sensitive, but are also in touch with the contact lens and are thus exposed to potential negative influences.
It is known for decades that chronic friction by a contact lens may negatively influence e.g. the fine structure of the conjunctival surface and thus reduce the wettability of the ocular surface. A typical side-effect in long-term contact lens wear is the potential development of Dry Eye symptoms of varying degrees.
Speciality Contact Lenses can serve as a medical tool
Apart from the fact that Contact Lenses can exert unwanted side effects on the ocular surface and tears Contact Lenses can also be used as a medical tool in selected cases.
The easiest case is probably when a soft Contact Lens is used as a clinical bandage lens to promote healing after surgery or in cases of recurrent corneal defects (erosions)
Several types of Speciality Contact Lenses exist that can be used as medical tools in selected medical conditions for patients who are in continuous clinical control.
This refers to ´Rigid´ Contact Lenses that can correct higher degrees of corneal shape distortion (as occurs in higher astigmatism and in keratoconus) where the visual acuity can not be sufficiently corrected by spectacles.
´Rigid´ Contact lenses can also be used for intended changes of the corneal shape, termed as ´Orthokeratology´ in order to avoid day time wear of spectacles - which certainly needs close clinical monitoring.
Even though contact lenses lead to alterations of the ocular surface fine structure with occurrence of dry eye symptoms ...
... Speciality Contact Lenses (Scleral Lenses) can be used as a medical tool in patients with severe Dry Eye Disease.
Scleral Contact Lenses provide a protecting translucent cover over the sensitive cornea and preserves the patient´s few own tears under the vault of the contact lens against evaporation. This can typically restore ocular surface healing and visual acuity.
When basic rules of hygienic contact lens wear are not respected this can still result in dangerous ocular infections that may endanger vision.
Even with application of the most advanced medical therapy, a severe contact lens related corneal infection may tragically lead to a loss of the eye.
Bacteria are typically introduced through the handling of the contact lens by the wearer and/or by use of contaminated tap water. Bacteria accumulate in the contact lens containers or in difficult to remove deposits on the contact lens itself.
The occurrence of infection is further promoted by the inevitable occurrence of tissue microtrauma of different kind in contact lens wear. This provides a route of entry through the normally almost impenetrable ocular surface barrier.
Particularly inexperienced Contact Lens wearers are at risk for serious ocular infections. Furthermore patient groups with a reduced level of immune defense such as children and elderly people are particularly susceptible to ocular surface infections.
The increased use of daily disposable contact lenses contributes to a decrease in ocular infections. because the critical steps of cleaning and storage of a worn lens become obsolete.
Deeper INSIGHT into ...
The Ocular Surface
The OCULAR SURFACE must be constantly moist to provide its health and thus perfect vision.
=> The moist tissue at the anterior side of the eye ball !
What IS the Ocular Surface ?
The OCULAR SURFACE is the moist mucosal tissue at the anterior side of the eye ball. Apart from the readily visible Cornea and Conjunctiva that are bathed in the tears it consists of the Lacrimal Gland for production and of the Lacrimal Drainage System for disposal of the ´used´ tear fluid.
The CONJUNCTIVA is a maintenance organ for the cornea that contributes to the health of the cornea. It covers the front side of the eye ball and the back side of the eye lids and thus forms the conjunctival sac that is open to the outside only at the palpebral fissure where the tissue is covered by a film of tears - the tear film. (The width of the conjunctival sac and tear film are greatly exaggerated in the schematic drawing for didactic reasons - normally the eye lids basically touch the globe and transform the ´real´ conjunctival sac into a mere moist slit between the eye lids and the eye ball and the tear film is very thin.).
=> To preserve its health and integrity !
Why is the Ocular Surface Moist ?
The Ocular Surface is a moist mucosal tissue to keep the Cornea transparent.
It must be kept constantly MOIST – everywhere and every time – to remain healthy and intact and the Ocular Surface is thus constantly bathed in the tear fluid.
The vehicle for moisture are the TEARS that are produced by the ocular glands and disposed by the lacrimal drainage system into the nose.
The turnover of tears at the ocular surface is shown in the animation to the right..
TEARS are the essence and Medium of moisture at the Ocular Surface
The Tear FLUID, usually simply termed as ´TEARS´ is produced by the Glands of the Ocular Surface. After their ´usage´ at the Ocular Surface, which refers to the bathing of the cornea and conjunctiva, the tears are discharged from the bulbar surface into the lacrimal drainage system towards the nose.
The continuous production of new tear tears and their flow over the ocular surface is therefore of utmost importance for the Health and Clarity of the CORNEA and thus for intact VISION.
Also, the regulated disposal of ´used tears´ from the ocularsurface is very important because there is very little space on the ocular surface for fluid.
Actually not even one drop of extra fluid, e.g. of eye drops, can typically be accommodated and thus most of it typically flows away over the lid margin
In contrast to a DRY Eye, with a definite lack of tears, the increased productionof tears as seen in an irritated ´Watery´ Eye ... or, a decreased disposal of tears from the ocular surface, as seen in an abnormal eyelid shape termed as ´ectropion´ can also lead to problems. Both of these conditions with ´too many tears´ at the ocular surface typically lead to a (continuous) dripping of tears over the lid margin, that is termed ´epiphora´ by the clinician.
So ... we can see that the ocular surface is not too different from our experience in daily life - too much can be equally tiresome as too little
=> It provides Moisture and Vision !
What is the Tear FILM ... and what is it good for ?
Constant moisture of the cornea and conjunctiva in the opened palpebral fissure is achieved by covering them with a layer of tear fluid – The TEAR FILM.
This is thin and homogeneous enough not to impair vision and at the same time sufficiently stable to avoid desiccation of the tissue at the air atmosphere.
The Tear FILM has three layers constituted by the products of different glands. Mucins from single goblet cells (GC) in the conjunctiva make the surface wettable by the Water from the Lacrimal Gland. Oil from the Meibomian glands inside the eye lids forms the surface - it retards evaporation of the tear water and provides stability of the tear film.
They spread the essential pre-ocular Tear FILM !
What is the role of the Eye Lids?
The wiping movement of the upper eye lid during the blink spreads the tears into the thin and homogeneous Tear FILM - this is not only necessary for keeping the moisture of the tissue in theh palpebral fissure but it is, at the same time, the main surface for refraction of the light to provide perfect vision.
Necessary prerequisites for a stable Tear FILM and thus for ocular surface health and visual acuity are SECRETION of tear fluid by the glands and the FORMATION of the tear FILM by the wiping action of the eye lids …
... consequently an alteration of Gland function and/ or of Lid function may lead to a Dry Eye condition - if this occurs chronically it may result in Dry Eye Disease.
In addition to spreading the Tear Film from the tear fluid, the eye lid action during blinking also contributes to the drainage of the ´used´ tear fluid via the lacrimal drainage system into the nose.
The Healthy Ocular Surface is a Pre-Requisite for Vision !
WHY is the Ocular Surface so important ?
The healthy Ocular Surface provides the clear window of the eye to see the light from the environment.
Without a healthy ocular surface all later steps of the vision process are meaningless.
Some DETAILS on Dry Eye Disease
DRY EYE DISEASE is an impairment of permanent moisture of the Ocular Surface with subsequent Destruction of the Tissue and a Reduction of Visual Acuity.
=> An Alteration of the Tear FILM that typically leads to Damage of the Ocular Surface Tissue
What is DRY EYE DISEASE?
Dry Eye Disease is often termed as ´KeratoConjunctivitis Sicca´ (KCS) or simply known as ´Dry Eyes´, Burning Eyes, Itchy Eyes, Heavy Eye Lids, Tired Eyes ... and many other colloquial expressions that refer in one or the other way to ocular irritation.
Dry Eye Disease is a complex dysregulation of the functional anatomy of the ocular surface that impairs the permanent moisture and the integrity of the tissue and thus its health and the intact vision.
It typically goes along with signs and symptoms of ocular dryness, ocular irritation, tissue destruction and pain as well as with visual impairment, mainly in the sense of fluctuating visual acuity. and blurred vision.
A Deficiency in the PRODUCTION of Tear Components and/ or a deficiency in the FORMATION stable tear film are the main causative factors that lead to subsequent desiccation and damage of the tissue
WHAT are the CAUSATIVE FACTORS for Dry Eye Disease ?
Basic CAUSATIVE FACTORS for the pathology are:
- (1) a Deficiency of Gland SECRETION/ Tear PRODUCTION by any pathology of the ocular glands that leads to an insufficient quantity and/ or quality of tears and/or
- (2) a Deficiency in the FORMATION of a sufficiently stable Tear FILM from the available secretions, by any eye lid or blinking problem (termed as Lid- and Blinking Dysfunction - LBD).
The alterations in the function of the ocular glands and/ or of the blinking mechanism lead to INSTABILITY of the Tear FILM and thus to impairment of permanent ocular surface wetting. Insufficient wetting then results in DAMAGE of the Ocular Surface Tissue !
in Dry Eye Disease
Typical subjective SYMPTOMS are various degrees of Ocular Dryness, Blurred Vision, Irritation and Pain !
What are typical SYMPTOMS of Dry Eye Disease?
The basic causative factors of insufficient secretion and/or insufficient tear film formation typically lead to SYMPTOMS such as::
- Dryness, grittiness, and foreign body sensation
initially, occasional episodes of increased tear flow and watery eyes can alternate with eye dryness
- Burning or stinging
- Irritation of varying degrees or pain
- Unstable visual acuity/ Blurred Vision
e.g. intermittent blurred vision that comes and goes and becomes better upon enforced blinking
- Moderate degree of eye redness
- ´Heavy´ eye lids or ´tired´ eyes or
- Contact lens wear is or becomes uncomfortable or impossible
in Dry Eye Disease
Typical objective clinical SIGNS of Dry Eye Disease are a reduced tear volume on the ocular surface and/ or a reduced tear film stability that reduce the moisture of the tissue and lead to surface damage !
What are typical SIGNS of Dry Eye Disease ?
The lack of sufficient tear fluid or of a sufficiently stable tear film that is often caused by a Dysfunction of the Meibomian Glands (MGD) results in respective pathological SIGNS: of the Eye Lids, Lid margins and Meibomian Glands as well as of the Tears, the Tear Film and of the Corneal and Conjunctival Epithelial Surface:
the tear film ruptures Quickly and has a short ´break up time´ (BUT)
- this is typically evaluated by staining the tear film with blueish-green stain (fluorescein) in order to make break-up of the tear film visible
- the animated schematic diagram to the right illustrates a highly pathologic tear film that is stable for only one single second - whereas a normal value should be at least ten seconds or longer (until the tear film ruptures and triggers another blink to reform a new tear film).
initially, occasional episodes of increased tear flow and watery eyes can alternate with eye dryness
there is a Low tear volume on the Ocular Surface
- this is detectable as a low tear meniscus height (TMH) and, more precisely, as a decreased radius of the tear meniscus curvature
- due to either increased evaporation of tear water due to a deficiency of oil secretion (this is the main primary reason - termed evaporative dry eye)
- or due to decreased secretion of aqueous tears from the lacrimal gland (termed primary aqueous deficient dry eye)
Deficient/ thin oil layer on the tear film
- typical consequence of Meibomian Gland Dysfunction (MGD) - the main primary cause of Dry Eye Disease
Lid Margin Alterations, such as:
- Meibomian gland orifices with pouting or plugging by inspissated material
- increased redness andincreased blood vessels (teleangiektasia)
- foam and debris on the lid margin
- rounding and irregularity of the posterior lid margin
Defects of the epithelial tissue that covers the Ocular Surface (Epithelial Vital Staining)
- of the Cornea and Conjunctiva
- of the Lid Margin as Lid Wiper Epitheliopathy (LWE)
Elevated levels of inflammatory mediators in the tears and tissue
- inflammatory cytokines, chemokines
- downstream activation of tissue degrading enzymes
Lid-Parallel Conjunctival Folds (LIPCOF) along the lid margin
- as a sign of tissue destruction due to activation of tissue degrading Matrix-Metalloproteinase (mainly MMP9) enzymes
Disappearance of Meibomian gland tissue (Gland Drop-Out)
- in visualization of the glands by specific techniques (Meibography)
in Dry Eye Disease
=> ... this is not completely clear as yet and still an issue of ongoing scientific investigations!
WHY are the subjective SYMPTOMS and the clinical SIGNS in Dry Eye Disease often disparate?
In Dry EYE DISEASE there is often a Disparity between subjective Symptoms of the Patient and the objective clinical Signs
In some cases intense subjective symptoms are causing a severe suffering of the patient whereas the clinical investigation may only observe few minor manifest alterations or even now pathology - this may probably point to a potential chronic pain syndrome.
On the other hand there may be a patient who in fact has severe objective alterations on the normal structure and function but does not suffer from any severe or may probably have no symptoms at all. Such a patient may then have only a limited interest in therapeutic interventions even though these may be very advisable from a clinical perspective.
The processing of signals from the Ocular Surface is complex and is influenced on different levels of the nervous system. Therefore, the outcome depends on many variable and may very well be different in different individuals. This fits well with the observations from our daily lives, that different people tend to have different ´nerve costumes´ and may react differently to different stimuli.
Another issue is, that there is a principal difference between a ´perception´ e.g. of touch in a peripheral organ, such as the cornea, and something that we call pain.
PAIN is not not a mere perception but is basically more of a feeling, because it contains an emotional aspect that the brain allocates to an incoming afferent impulse from the periphery The emotional aspect that the brain allocates to the stimulus is based on very individual things like previous experiences, recent emotions,or future expectations ... in order to name just a few factors. Therefore the actual feeling that is generated in the brain can vary to a large degree in different individuals. This may point to a neuro-biological possibility for explanation of the disparity of signs and symptoms in Dry Eye Disease.
Pain has the biological sense to alert us in order to avoid dangers that may threaten our health or our life. Under certain conditions when a pain becomes chronic and when it leads to a damage of the nervous system itself, it can develop into a chronic PAIN SYNDROME. Pain has then lost its biological function and becomes a disease of its own. In such cases where chronic pain persists without an identifiable tissue damage it may be useful to seek the help of a pain specialist.
How do we GET Dry Eye ... and Why does it get WORSE?
Dry Eye Disease is strongly influenced by Regulatory Systems and Risk Factors
How do we GET Dry Eye Disease ?
Several factors influence the function of the Ocular Surface.
An impairment of positive factors and the occurrence of negative factors both decreases the normal function of the tissue and thus increase the likeliness and severity of a potential Dry Eye Disease.
The complex dysregulation of the functional anatomy of the ocular surface in Dry Eye Disease with a deficiency of the basic functional complexes for permanent moisture is influenced by different factors:
Failure of regulation
Failure of mainly the Nervous System, Endocrine Hormonal System, and the Immune System deteriorates the function of the Ocular Surface. Age and female Sex, related to a predominating estrogen action with relative lack of androgens, appear as the main predisposing factors for a higher risk of Dry Eye Disease
external Risk factors
Negative external influence Factors represent RISK factors for disease. They Influence the tears on the Surface and can override the normal functional capacity. They mainly occur in desiccating environments, contact lens wear, visual tasks with low blinking frequency. Many occur combined in typical office work environments and may lead to a Dry Eye Condition termed "Office Eye".
internal Risk factors
Alteration of organ Health
Negative internal influence Factors represent RISK factors of the onset of disease. They act on the tissues that produce the tear fluid and can deteriorate the normal function. These are e.g. chronic diseases, chronic medication, age, sex, nutrition or hydration etc.
Tear Film Deficiency with decreased wettingof the tissue and Tissue Damage negatively influence each other in self enforcing vicious circles and lead to progression of disease !
The two typical pathologies In Dry Eye Disease are
- Tear FILM DEFICIENCY and
- Surface TISSUE DAMAGE
Tear Film Deficiency and Surface Damage influence each other negatively and are therefore linked by self-enforcing vicious circles that lead to worsening of the condition.
When is a Dry Eye ... a DISEASE
When ´Dry Eyes´ become chronic an occasional condition of ocular dryness can turn into a disease !
WHEN does a "Dry" Eye turn into Dry Eye DISEASE ?
AN OCCASIONAL “DRY” EYE IS NOT YET A DISEASE
Most of us have probably already had an occasional sensation of a “dry” eye, e.g. when we are exposed to an unusually dry and desiccating environment, characterized by Low humidity, hot temperatures, high wind speeds and/ or by Low blinking frequency due to intensely concentrated visual task as e.g. in screen work
Such a “dry” eye is is typically a short-lived condition that disappears as soon as we become aware of it and remove the described desiccating stimulus.
WHEN “DRYNESS” BECOMES CHRONIC THE CONDITION TURNS INTO A DISEASE
Only when the feeling of “Dryness” remains constantly and cannot be removed or sufficiently improved by avoiding desiccating environmental stimuli and/or by improving blinking
… then the conditions becomes chronic and an occasional “Dry” Eye may develop into Dry Eye DISEASE.
This is typically related to an increase in duration and intensity of symptoms and by increasing severity of clinical findings/ signs due to increasing alteration and wounding of the ocular surface tissue
Several Different and Interacting self-enforcing VICIOUS CIRCLES of disease aggravation and worsening occur in chronic Dry Eye Disease and can lead to the full blown clinical picture with a progressive tissue destruction and a loss of function of the ocular surface.