O que você sempre quis saber sobre o OLHO SECO ... e nunca ousou perguntar!
--- Fatos sobre o olho seco ... Causas do olho seco
... Tratamento do Olho Seco
... O que posso fazer contra um olho seco?
... Terapia do olho seco ...
Dry Eye Disease is a chronic irritation and damage to the ocular surface - the moist tissue on the front of the eye with the eyelids.
It is typically triggered by a lack of the tear film on the eye.
The ophthalmologist refers to this disease as keratoconjunctivitis sicca, i.e. " dryness inflammation of the cornea and conjunctiva ".
THERAPY : => Timely and adequate treatment of dry eye disease is important to avoid permanent damage to vision.
The good news is that every patient can do a great deal of self-improvement to relieve dry eye symptoms.
Not every dry eye is recognized correctly , because the symptoms are often uncharacteristic at first and the onset is often creeping.
Most complaints in the Dry Eye Disease are explained by the irritation of the eye and the disturbance of the tear film :
This leads to ... " tired eyes ", "heavy eyelids" or "glued eyes"
Dry eye pain can occur in different regions:
Persistent eye irritation can lead to pain and chronic pain can lead to pain syndromes. Chronic Pain Syndromes are a distinct disease factor in Dry Eye Disease and are often difficult to treat. Collaboration with pain medicine and psychosomatics can be helpful here.
In Dry Eye Disease, the homogeneous thin tear film, that is important for a good visual acuity, is disturbed. Therefore, many patients have vision problems like
THERAPY => Visual disturbances in the dry eye typically improve, or even disappear temporarily, after one or several forceful eyelid blinks, that spread a new and stable tear film. - This is also a good test of whether visual disturbances are due to a tear film disorder.
Other reasons for a wet eye and tears over the edge of the lid can be:
THERAPY => Here, a close examination by the ophthalmologist and maybe a small surgery may be useful.
What does the tear film consist of ? - Of the secretions from the Ocular Glands !
How is the tear film made ? - The Eyelids spread the Tear Film !
Where does the tear film go to ? - The tears are drained into the nose !
A tear film deficiency can be caused by a defect in:
Only rarely a tissue disorder occurs first and later disturbs the tear film, as occurs e.g. in:
Chronic inflammatory disease such as in rheumatic diseases or in the immune response after bone marrow transplantation (graft-versus-host disease, GvHD).
A lack of water is often thought be caused by a reduced production of watery tears through the lacrimal gland. However, a primary lack of water due to a disturbance of the lacrimal gland is very rare.
Much more common is (secondary) water loss due to increased evaporation of the tear water on the ocular surface. This occurs in case of oil deficiency and is made worse by desiccating environmental influences.
Tear film deficiency causes tissue damage to the ocular surface, whether caused by increased evaporation or by primary low lacrimal gland production
THERAPY => Aqueous eye drops, with or without added oil, are a useful therapy.
... They should be used as needed and often enough, up to 1x per hour. An even more frequent use of aqueous eye drops is usually not useful, as this can reduce the effect of your own (residual) tears and thereby the irritation of the eye can be worse.
Most often, not the water of tears is missing first, but the superficial layer of oil on the tear film, which reduces the evaporation of the water.
Lack of oil is usually caused by disorders of the meibomian glands in the eyelids . When the glands clog, oil is missing and the watery tears evaporate faster, leaving the eye dry. Meibomian gland disorders are very common and increase with age .
THERAPY => Eye drops that contain oil or a lipid spray can help here ... but ...
... above all, it is important to improve the function of the oil-producing meibomian glands in the eyelids again ! This is done by a physical lid therapy (with warming, massage, cleansing), which the patient himself performs regularly at home to improve the blockage and damage to the glands.
The regular eyelid strike, termed as the ´BLINK´, is performed by the action of the internal eyelid muscles, and is necessary:
Rare blinking and incomplete blinking are common causes of a tear film deficiency.
The Office Eye / Office Eye is a fast-growing form of dry eye in "modern" office work environments . This can add up several harmful effects and thus lead faster to a dry eye. This form of dry eye not only affects the elderly but also occurs more frequently in younger people .
Concentrated visual work (eg computer, television, driving) is accompanied by rare blinking and therefore easily leads to a dry eye .
The danger of a dry eye is getting bigger:
In addition to an unstable tear film still drying environmental factors and perhaps negative internal influences on the tear production are added.
THERAPY => My observation and, if necessary, change of the eyelid are important here, for a sufficiently frequent and complete eyelid strike. Furthermore, deliberate Blink exercises at work can be useful - there are even computer apps to remember. Furthermore, avoidance to dry working environments, sufficient breaks and sufficient drinking volume are helpful.
A tear disorder induces or exacerbates the irritation of the ocular surface.
An irritated ocular surface, in turn, worsens the stability of the tear film on the damaged ocular surface.
Tear Deficiency and and Ocular Surface Tissue Damage are obviously linked by a so-called "Vicious circle" where the dysfunction of one makes the other worse - which then reinforces the starting event ... and so on.
Therefore, dry eye disease has a tendency to aggravate itself if not treated adequately.
THERAPY => An interruption of the harmful self-aggravation (Vicious Circles) can be done by:
If the ocular surface is permanently irritated, as is typical in the dry eye, then this can trigger an inflammatory reaction. The inflammation is actually the defense of the eye. But if the inflammation occurs permanently, then it can increase the self-aggravation of the dry eye.
THERAPY => here an anti-inflammatory therapy by the ophthalmologist may be useful.
The ophthalmologist you trust and, for severe cases, even in specialized Sicca centers, there are even more therapy options available.
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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"
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.
An increased tear flow in case of watering eyes can indicate 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.
Another reason for watering eyes with tear overflow over the eyelid border, medically termed as ´epiphora´, can occur due to eyelid deformations. Because eyes with eyelid deformations cannot form a normal tear film or cannot hold it on the ocular surface these conditions also lead to Dry Eye Disease with ocular irritation.
Frequent eyelid deformations are e.g. an inward or outward twist of the eyelid margin (ectropion or entropion) that typically occurs with tissue changes in advancing age.
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 on the surface of the tear film has the function to slow down the evaporation of tear water ... similar to a lid on a pot with warm 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 ocular surface disease - of which Dry Eye Disease is the most frequent one - for quite a while ... and researchers world-wide have 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.
... 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.
Choose your PAGE of Interest - or simply read along ... which may be most instructive:
Choose your CHAPTER of Interest - or simply read along ... which may be most instructive
The shining of the Ocular Surface comes from the Tear Film ...
... that maintains the permanent Moisture of the Ocular Surface.
Moisture is necessary for the health of the ocular surface tissue and moisture is also important for perfectly clear vision.
Without sufficient moisture the vision becomes blurry, the tissue is increasingly damaged, and sensations of discomfort occur.
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.
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´
The Tear Fluid is produced by several Ocular Glands.
There are three different types of glands needed, because the tear film on the eye consists of three different types of substances.
Tears are produced by the various Glands at the Ocular Surface.
The bulk volume consists of water and comes from the lacrimal gland that is located upstream in the upper lateral side of the bony orbit.
From there the tears enter the conjunctival sac. They are flowing over the visible anterior part of the eye and thus constantly bathe this area.
At the nasal side the ´used tears´ are sucked up by two narrow lacrimal puncta, one at each nasal end of the upper and lower eyelid.
Through the lacrimal drainage system the tears enter the nose. When tears go there in larger quantities, e.g. in emotional crying, they may flow backwards into the pharynx where we can sense their salty taste.
Meibomian oil protects the tear water from evaporation.
The Meibomian glands produce lipids that are liquid at body temperature and thus form an oil.
The glands are of particular importance for the health of the ocular surface because their oil retards the evaporation of the tear water from the lacrimal glands.
In the dry environment that we live in, even a copious secretion of tear water would rapidly evaporate from the ocular surface if it was not protected by the superficial Meibomian oil layer on the tear film.
The Meibomian glands form individual long bodies that fill the tarsal plates of our eyelids. About 25-30 glands can be found in every healthy eyelid and the little orifice is close onto the posterior lid margin ... as can be seen in an ordinary mirror, by everybody who is interested.
With every blink of the eyelids a little drop of oil is expressed by the lid muscle. It gets from the gland onto the eyelid margin and the tear film. where it protects the aqueous tear film from too rapid evaporation.
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 ocular surface and thereby provides a perfectly Smooth Surface layer for perfect refraction of the incoming light that allows for perfect Visual Acuity.
The Tears are transformed into the thin, homogeneous Tear Film ... through the coordinated Movement of the Eye Lids - the BLINK.
During the blink mainly the upper eye lid wipes over the anterior surface of the eyeball and thus distributes the tears into the very narrow Tear Film.
During the down-phase of the blink the old tear film is removed by the upper eyelid and during the up-phase the upper eyelid draws out a new intact homogeneous tear film.
It becomes obvious that any disruption of the EyeLid and of their normal Blink movement and speed is an important factor for the onset on a Dry Eye condition . This is termed as ´Eyelid and Blinking Disfunction´ (abbreviated as LBD).
Only through the coordinated blink movement of the eyelids, together with the very special composition of the Tears , is it possible to form a TEAR 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.
The formation and preservation of the Tear FILM is very laborious in the dry environment that we live in, and is thus very vulnerable.
The Tear Film depends on a multitude of very different Influence Factors, that can, in one or the other way, have a positive or negative influence.
All negative influence factors are Risk-Factors - they can, sooner or later, lead to a Dry Eye condition - particularly when they become chronic.
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 Tear Film has the function to prevent Drying of the Ocular Surface Tissue. Therefore the most immediate consequence of a Dry Eye condition is typically the Drying and thus Destruction of the Ocular Surface Tissue.
The eye lids can then often be sealed by sticky mucus and encrustations.
This results in a ´downstream´ irritation of nerve fibers They transmit ocular irritation of various degrees and can lead to pain that is often described on and around, occasionally behind, the eye. Inflammatory reactions can reinforce the whole process, eventually leading to severe tissue destruction and to a chronic pain syndrome.
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
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 a typical Tear Supplementation Therapy.
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.
The glands are blocked by inspissated secretum and excessive keratinization - therefore inspissated oil accumulates inside the glands.
Muscular force during blinking of the eyelids normally helps to express the oil from the Meibomian glands.
Rare Blinking is thought to be an important factor for a lack of oil on the tear film and possibly a co-factor for onset of gland dysfunction.
Intended forceful blinking is known as a simple way to increase the oil layer on the tear film and thus to improve tear film stability in order to prevent ocular surface dryness.
In most cases there is a deficiency of the Tear FILM based on a qualitative or quantitative lack of Tear Components.
Physical Eyelid 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 !
It appears necessary that Physical Therapy is done as a permanent therapy, at best twice a day - because a chronic disease typically requires a chronic therapy !
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 or even electrically heated and moistened googles may make the potentially laborious effort of physical therapy, twice a day, considerably 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.
... or, to re-phrase it in the Roman way: ´palpebra sana in corpore sano´ - unproven quote from Clarissimus GALEN ;-)
- - -
Various other THERAPY OPTIONS are discussed in other Chapters of the full length English Language Pages of the OSCB Information WebSite.
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 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.
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
Choose your CHAPTER of Interest - or simply read along ... which may be most instructive
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.
The Glands of the Ocular Surface for the production of the dfferent components of water, oil and slime/mucus together form the tear fluid.
The Tears are the essential medium for the provision of moisture at the Ocular Surface.
The Eye Lids spread the tears into the essential pre-ocular Tear Film.
The Tear Film makes it possible that moisture can even persist on the tissue within the opened palpebral fissure. In addition to moisture the Tear Film aids in allowing a perfect light refraction and thus a perfect vision at the same time.
The Healthy Ocular Surface is a Pre-Requisite for Vision and without it all later steps of the vision process are meaningless.
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.
Dry Eye Disease typically shows the two PATHOLOGIES of
The basic CAUSATIVE FACTORS for Dry Eye Disease are those that directly lead to the deficiency of the Tear FILM - this is
Such patho-physiological analysis of the disease process in Dry Eye Disease led to the ´Holistic Dynamic Concept´ of Dry Eye Disease as described in the Dry Eye Chapter of the original full length English language version of the OSCB WebSite.
The main clinical signs of Dry Eye Disease are thus:
Instability of the Tear Film is a typical feature of any type of Dry Eye Disease and thus important to be investigated.
Vital staining is a quick and easy way to verify another important feature of any type of Dry Eye Disease which is alteration, wounding and destruction of the normal epithelial structure
Tear Film Deficiency and Surface Damage lead to typical subjective irritative SYMPTOMS of the patient.
Typical Syptoms in Dry Eye Disease are e.g. ocular irritation, 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.
Initially the ocular irritation due to tissue alterations can lead to episodes of increased tearing, watery eyes and tear dripping over the lid margin.
The ONSET and PROGRESSION of Dry Eye Disease is strongly influenced by many different factors.
in Dry Eye Disease are
Tear Film Deficiency and Surface Damage influence each other negatively and are therefore linked by several self-enforcing vicious circles that lead to worsening of the condition.
are a typical component of Dry Eye Disease because inflammation represent a basic protective mechanism of wounded tissue - and this is also true for the Ocular Surface.
When the wounding becomes chronic the inflammatory answers of the tissue also become chronic and more severe.
Inflammatory pathways are thus an important disease mechanism for worsening of the condition in chronic ocular surface 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 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.
´Rigid´ Contact Lenses are typically smaller and exclusively rest on the cornea. They need a certain adaptation time for the wearer and are thus less widespread, but have superior inert material and optical quality.
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.
Movement of a Soft Contact Lens on the Surface of the Eyeball and behind the Eyelids. The Contact Lens moves with every gaze movement of the eyeball and also upon the frequent eye blinks. The amount of mechanical friction at the ocular surface is typically increased in contact lens wear, even when the tear film is sufficient.
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.
The fine structure of the surface epithelium may undergo a deterioration where it is exposed to the influence of a Contact Lens. Shown here is the change of the bulbar conjunctival epithelium in the excursion zone of a soft Contact Lens. The cubical surface cells with interspersed goblet cells for the production of water-adhesive mucins are replaced by a squamous epithelium without goblet cells in a process termed ´squamous metaplasia´.
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. Even though such contact lens impacts on the ocular surface may not necessarily be pathologic, they may still contribute to that is known as ´Contact Lens Discomfort´ (CLD). CLD refers to a vague irritative discomfort by sensing the presence of a contact lens on the eye and CLD was the topic and title of the 2013 TFOS report on such Contact Lens impacts on the Eye.
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.
It is shown that the structure of the bulbar conjunctiva changes in contact lens wear. This occurs in the zone where the margin of the contact lens is in touch with the surface and rubs over it upon every movement of the eye. The type of epithelium changes, termed as squamous metaplasia, and the number of goblet cells that produce the important mucus for the wetting of the surface, decrease in number. These alterations deteriorate the wetting of the Ocular Surface and promote the onset or worsening of Dry Eye Disease.
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 constitute a moist chamber that 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.
Modern contact lens types can often reduce many of the potential negative impacts on the ocular surface by technical improvements - An issue that is still relevant is, however, the HYGIENE.
Insufficient Hygiene is a crucial factor in Contact Lens wear and results in a higher rate of ocular infections in contact lens wearers. Microbes can be introduced by the fingers of the wearer or from the use of tap water, that should be omitted. Certain types microbes also occur on the normal ocular surface. Microbes grow on the lenses and in the storage containers and form adhesive ´biofilms´ that protect them against cleaning and removal.
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 eventually and 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.
Choose your CHAPTER of Interest - or simply read along ... which may be most instructive
The OCULAR SURFACE must be constantly moist to provide its health and thus perfect vision.
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.).
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 continuous Turnover of Tears at the Ocular Surface goes (1) from their main production in the lacrimal gland over (2) the readily visible cornea and conjunctiva that they must constantly bathe into (3) the lacrimal drainage system that drains the tears into the nose.
The Tear FLUID, usually simply termed as ´TEARS´ is produced/ secreted 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 ocular surface 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 real DRY Eye, with a definite lack of tears, the increased production of 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.
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.
A glimpse into the TEAR FILM. The main phase of the Tear Film overlying the transparent cornea is composed of the aqueous fluid from the lacrimal gland. Below are the numerous finger-like protrusions of the surface cells. Their cell bound and and loose secreted mucins (pink filaments) constitute the basal mucin layer that binds the tear water to the ocular cell surface. Mucins mix with the water and together they form a water-mucin gel. The surface of the Tear Film is covered by a very narrow oil layer from the-lipids of the Meibomian glands. The lipid layer has the same thickness and coloring as an oil film on a puddle of water. A main function of the oil layer is to retard the evaporation of the aqueous main phase of the tears. Consequently a lipid deficiency due to a dysfunction of the Meibomian glands is presently reported as the main causative factor for Dry Eye Disease.
This schematic animated diagram illustrates the principal eye lid function of tear spreading - actual tear drops occur in the palpebral fissure only during increased tear secretion.
The wiping movement of the upper eyelid during the blink spreads the tears into the thin and homogeneous Tear FILM.
Of particular importance at the eyelid margin is the posterior lid border because this is the structure that distributes the tears into a very thin film of tears. The posterior lid border acts similar to the wiper blade at the windscreen of car. It is therefore termed the lid wiper.
This blink movement of the Eyelids is not only necessary for keeping the moisture of the tissue in the palpebral fissure ...
The wiping movement of the upper eyelid during the blink spreads the tears into the thin and homogeneous Tear FILM.
This blink movement of the Eyelids is not only necessary for keeping the moisture of the tissue in the palpebral fissure ...
... but, at the same time, the tear film is the main surface for refraction of the light to provide perfect vision.
Another function of the blink is that the force of the lid muscle expresses some oil from Meibomian oil glands inside the Eyelids.
A lack of blinking therefore leads to a lack of oil on the tear film and to its instability.
In conclusion, the 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 blinking action of the eyelids …
... consequently an alteration of Gland function and/ or of Eyelid 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 eyelid 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 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.
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.
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.
Basic CAUSATIVE FACTORS for the pathology are:
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 !
The basic causative factors of insufficient secretion and/or insufficient tear film formation ...
... lead to the primary pathologies of Tear Film instability and subsequent Drying and Damage of the Tissue
These two pathologies explain the typically SYMPTOMS in Dry Eye Disease::
e.g. intermittent blurred vision that comes and goes and becomes better upon enforced blinking - which is good evidence that the symptoms indeed derive from a Dry Eye condition.
A moderate DRY EYE typically shows only mild redness of the Conjunctiva and Lid Margins that may indicate an inflammatory condition as described by the term ´Keratoconjunctivitis sicca´. The orifices of the Meibomian oil glands are often obstructed by visible or invisible inspissated secretum (which represents the most frequent primary cause of Dry Eye Disease). The tear volume is low due to water evaporation and the tissue of the Ocular Surface epithelium has many small defects, that occur as small spots in vital staining with a green stain (fluorescein) observed in blue light.
The lack of sufficient tear fluid or a lack of a sufficiently stable Tear Film, that is often caused by a Dysfunction of the Meibomian Glands (MGD), results in the pathological SIGNS of the Dry Eye Disease.
The typical signs of Dry Eye Disease are important to known and are useful for the Diagnosis:
initially, occasional episodes of increased tear flow and watery eyes can alternate with eye dryness
In Dry EYE DISEASE there is often a Disparity between subjective Symptoms of the Patient and the objective clinical Signs points to some considerations on the neurobiology.
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 variables 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 the same 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 the allocations that subcortical centers add to it in order to produce something that we call pain.
PAIN is not a mere perception but is basically more of a feeling, i.e. a construction of the brain, 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 explanation of the disparity of signs and symptoms in Dry Eye Disease.
However, for the respective individual, the two different neurobiological authorities of "perception´ and of ´pain´ are not always clearly discernible ... and it is not always clear which of the authorities is more ´real´ and thus trustworthy.
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.
The subjective emotional rating of a sensation may very well dominate over the pure perception ... or reverse. 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 of the normal structure and function but does not suffer from any severe symptoms 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.
Psychosomatic Influence on a disease process and on its self-perception by the patient are an established and well recognized part of medicine for a long term. Apart from e.g. back pain, cardiovaculatory dysfunction, and intestinal dysfunction, a psychosomatic component can play an important role also in Dry Eye Disease, as confirmed by many studies. When the disease becomes the main concern in daily life this may suggest that it could be useful to seek the help of psychosomatics.
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 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
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".
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.
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.
Inflammation is an important mechanism for worsening of Dry Eye Disease.
Inflammation is a basic protective mechanism of cells and tissues against wounding and destruction, as typically occurs in Dry Eye Disease due to tear film instability and increased friction. Inflammation initiates destructive mechanism in order to overcome the ´destructor´ and is later followed by tissue repair.
When inflammation becomes chronic, however, it transforms into a negative and destructive process because the initial destruction can not be followed by a sufficient repair.
In chronic diseases like Dry Eye Disease, the chronic tissue wounding may lead to a chronic inflammation that drives some vicious circles and can thus greatly enhance the disease process.
Dry Eye Therapy to interrupt the vicious circles in Dry Eye Disease may then include an anti-inflammatory therapy for a limited time in addition to a sufficient Tear Supplementation and Eyelid Therapy .
For more detailed information on THERAPY in Dry Eye Disease please see the Full Length English Language Pages of the OSCB
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 tasks 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.
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.
