The Ocular Surface is a complex and delicate arrangement of organs at the front of the eye ball that provides a moist environment in order to perform the first steps of the Vision Process. The moist mucosal organs at the anterior side of the Eye Ball form a continuous Anatomical Unit. It consists of the Ocular Surface Proper (Cornea and Conjunctiva - the organs that are continuously bathed by the tears) and of the Ocular Surface Mucosal Adnexa (Lacrimal Gland and Lacrimal Drainage System - the organs that manage the tears, i.e. that produce them or dispose them, respectively). Regulatory Systems maintain the intact function of the organs and thus join the Anatomical Ocular Surface into the Functional Unit. The Ocular Surface is a pre-requisite for Vision. Moisture - by the tears - is Key at the Ocular Surface. Moisture must be produced by the ocular surface glands - this is Secretion. Moisture must be spread into a Tear Film to provide permanent moisture in the palpebral fissure - this is Tear Film Formation. Dysfunction of the Ocular Surface Functional Unit leads to Disease - prototypic is Dry Eye Disease.
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The ocular surface is a complex and delicate arrangement of organs at the front of the eye ball that provides a moist environment in order to perform the first steps of the VISION Process
Contribution of the Ocular Surface Center Berlin (OSCB) to Ocular Surface Research
Members of the Ocular Surface Center Berlin (OSCB) have devoted their scientific energy to the concept of an Ocular Surface Unit for about 3 decades. Nowadays this is a cornerstone for the conceptual understanding of health and disease at the ocular surface.
The ocular surface consists of the moist mucosal organs at the anterior surface of the eye. They are a continuous anatomical unit from the lacrimal gland over the conjunctiva & cornea into the lacrimal drainage system.
The ocular surface organs are joined by several systems e.g. the flow of tears along the mucosal surface and they are regulated by the same systems, e.g. nerves, hormones and the immune system - thus they also form a functional unit.
The main function of the Ocular Surface is to provide the necessary equipment for VISION ... in the form of permitting the entrance of light into the eye and for its refraction.
Any dysfunctions in the unit, due to underlying regulatory systems or environmental influence factors, potentially results in ocular surface disease mainly Dry Eye Disease
The Ocular Surface consists of the moist mucosal organs at the anterior side of the eye ball that form an ANATOMICAL UNIT
The ORGANS of the OCULAR SURFACE form a continuous the Anatomical Unit of
the Ocular Surface PROPER
´... the (in-visible) organs that are bathed by the tears´
as a transparent window of the brain to the outside world
The cornea is the ´nerd´ of the ocular surface with high-tech function ... however in a very limited spectrum
main support tissue for the Cornea that hat many functions and provides, moisture, nutrition and protection
has a much larger surface because it covers the
anterior surface of the globe and the
posterior surface of the eyelids
contains all components that the Cornea can not have in the interest of transparency, e.g.
blood and lymph vessels
The conjunctiva is the ´maintenance genius´ for the ocular surface ... and thus for the whole eye and for vision
the Ocular Surface Mucosal ADNEXA
´... the (in-visible) organs that manage the tears´
´Home of the aqueous tears´ - it produces the bulk aqueous tear flow that reaches the downstream Conjunctiva and Cornea via its several excretory duct
... which is certainly a simpli-fication because the lacrimal gland produces many other important ingredients apart from just water
LACRIMAL DRAINAGE SYSTEM
´The sewer pipe for the aqueous tears´ - it drains the tear fluid, after bathing the ocular surface, into the nose
... which is again a simplification, as there are also several other functions - but it is good enough for now
All the mucosal organs of the OCULAR SURFACE PROPER and of its mucosal ADNEXA are anatomically continuous and form an anatomical unit.
REGULATORY SYSTEMS maintain the intact function of the organs and thus join the Anatomical Ocular Surface into the Functional Unit
The healthy function of the ocular surface organs is established and maintained by an intricate interacting network of regulatory systems such as
the nervous system,
the endocrine hormonal system and
the immune system.
Furthermore there is a plethora of other soluble factors that come with the blood circulation or are locally produced and ensure the growth, maturation, regeneration and ´special functions´, such as protective reactions and inflammation, of the tissues and organs.
The regulatory systems transform the anatomically continuous organs of the anatomical unit into the ocular surface functional unit. For more details please see e.g. the Section on ´Regulatory Systems´.
The Ocular Surface is a pre-requisite for VISION
The ocular surface provides the clear optical media for entrance of light into the eye and for its refraction to have a clear image of the outside world.
All later events inside the eye for
further transmission and refraction/ accomodation of the light for near and far distances ... or
for its reception by the photo-receptors of the retina ... or
for the neural transduction of signals in the nerve fibers to the visual cortex of the brain
can be drastically impaired or become meaningless IF the ocular surface is not intact.
The ocular surface is thus of utmost importance for vision and any dysfunction or disease of the ocular surface immediately endangers visual acuity.
MOISTURE — by the tears — is key at the Ocular Surface
1. Moisture must be produced by the glands - this is SECRETION
The organs of the mucosal adnexa, that are not readily seen in clinics, can be termed upstream and downstream of the ocular surface proper (cornea and conjunctiva).
This points to the high importance of the tear fluid, that ´flows´ along this paths, to provide ocular surface integrity, health and function.
"MOISTURE is key at the ocular surface" because
moisture keeps the optical medium of the cornea TRANSPARENT for the entrance of light into the eye and, probably equally important,
2. Moisture must be spread into a tear film to provide permanent moisture in the palpebral fissure- this is Tear Film FORMATION
Moisture must be spread into a FILM of Tears in front of the cornea and conjunctiva at the anterior side of the eye ball in the palpebral fissure. The FORMATION of the pre-corneal Tear FILM is achieved by the Blinking movement of the eye lids.
This importance of the pre-corneal TEAR FILM has at least two main reasons:
For the Mucosal Organs the essential MOISTURE must be be guaranteed always & everywhere. This puts the Ocular Surface into a DILEMMA:
in the palpebral fissure the bulbar cornea and conjunctiva are exposed to the ambient air atmosphere and are thus at risk of desiccation
on the other hand, when the eye lids were constantly closed this would be safe for the mucosa ... but no light could get into the eye for vision
This Dilemma is elegantly solved by the Ocular Surface: the transparent cornea is constantly covered with a very thin and homogeneous tear film. By this ´trick of nature´ the mucosal surface is kept moist every-where and every-time and light can still get into the eye.
The solution wouldn´t be half as elegant, if this ´trick´ wouldn´t provide another important function, because the very smooth surface of the pre-corneal tear film is at the same time the main refraction element of the eye and thus of the of utmost importance to achieve optimal visual acuity.
... here we already have a hint to understand, why one frequent symptom of Dry Eye Disease, that typically goes along with alterations of the pre-corneal tear film, is an unstable visual acuity.
Dysfunction of the Ocular Surface Functional Unit leads to Disease - prototypic is Dry Eye Disease
When components of the ocular surface functional unit are impaired and thus become dys-functional beyond a certain limit, this includes a risk of downstream pathological consequences.
All together the intricate network of structure and function at the ocular surface is keeping a delicate functional balance to preserve the moist mucosal niche in a dry environment ... and may easily become ill.
In view of the complex task that the ocular surface has, it is fair to say, that the system turns out to be surprisingly robust in our daily lives.
Nevertheless, many disturbances of the ocular surface functional unit, at least when they are chronic, can lead to pathology.
This will eventually also affect the most basic functional complex of the ocular surface - which is the provision of moisture. Therefore Dry Eye Disease is a prototypic disease of the ocular surface.