DEEPER INSIGHT into ...
Contact Lens DISCOMFORT (CLD)
Contact Lens Discomfort (CLD) is a major cause for discontinuation of CL wear
Even though amazing advancements have been made in design and material properties - contact lenses are certainly not yet perfect and may still cause sensations of ´feeling´ the contact lens on the eye – which may be quite vexing for some wearers.
Such unpleasant sensations and other minor side effects, that do not necessarily seem to reflect real pathologies, are still leading to many dis-satisfied contact lens wearers. A large percentage of them are ´dropping out´, i.e. they discontinue contact lens wear.
This condition was, by the respective TFOS International Workshop on Contact Lenses, termed as Contact Lens Discomfort (CLD). The initiative of the international scientific non-profit organization Tear Film and Ocular Surface Society (TFOS) has delivered the respective TFOS CLD REPORT in 2013.
Contact Lens Discomfort is difficult to be related to any concrete events and influence factors
The TFOS CLD Workshop addressed numerous issues around the topic of discomfort in contact lens wear including the underlying anatomy and cell biology, neural sensitization questions, suggestions on future study objectives and resulting potential therapy options.
The TFOS CLD REPORT has found enormous world-wide interest in the field and has led to considerable deeper insight into the topic. This report and other TFOS reports are freely available online at the TFOS homepage (www.tearfilm.org).
LID WIPER EPITHELIOPATHY occurs in Contact Lens Wear and is the most sensitive indicator for increased mechanical stress
One of the few conditions that could by identified to be likely associated with contact lens discomfort (CLD) is LID WIPER EPITHELIOPATHY (LWE).
The Lid Wiper is a specialised epithelial thickening of the posterior lid border (the Lid Wiper) is the surface.
It is in most direct contact with the eye balls and it distributes the tears into the thin pre-ocular tear film during the up-stroke of the blink.
Increased friction due to Contact Lens wear causes vital staining of the LID WIPER Epithelium of the posterior Lid Border
Therefore, the posterior lid border is the region that is exposed to the highest amount of friction between the eye lids and the eye ball. In any event where the friction is increased, e.g. in Dry Eye Disease or in Contact Lens wear, the Lid Wiper of the posterior lid border will conceivably suffer first and probably most.
There is evidence for this concept because destruction of the Lid Wiper epithelium, identified and termed as ´Lid Wiper Epitheliopathy´ by Donald KORB, Boston, was found to be the first an most sensitive indicator of increased mechanical stress at the ocular Surface.
FRICTIONAL FORCES ARE A MAIN IMPACT also at the Surface of the EYEBALL - on the Bulbar Conjunctiva
A main side effect of contact lenses occurs due to the direct mechanical impact, i.e. friction.
Even though contact lenses should basically be swimming in the tear film it is still practically unavoidable that they frequently come into touch with the adjacent tissue.
This is particularly relevant, when movements between the contact lens and the tissue occur. This happens all the time because the eye is rarely totally quiescent.
The contact lens moves over the ocular tissues: during:
movements of the eyeball during different directions of gaze
- blinking - movement of the upper eyelid over the contact lens with additional upward movement of the eyeball (BELL´s phenomenon)
- in extended contact lens wear overnight, when the eyeball can make ´Rapid Eye ;Movements´ during the REM-phases in sleep
Particularly important appears the margin of the contact lens, that does not only represent a ´stumbling block´ for the posterior lid border during a blink, but is likely also a main factor for interaction with the bulbar conjunctiva.
Contact Lens Wear causes Squamous Metaplasia of the ConjunctIval Epithelium
Studies have shown that not only rigid contact lenses but also soft contact lenses cause a distinct change of the bulbar conjunctival epithelium that is termed as squamous metaplasia..This is a distinct change of the cell type from spherical to flat together with changes in the number of goblet cells - typically a disappearance of goblet cells. This results in reduced wetting of the ocular surface and may thus pave the way for a development of a dry eye condition.
These changes are typically restricted to the excursion zone (please see the figure above) of the contact lens on the bulbar surface but this can easily extend for about one centimeter or more beyond the corneal limbus. The cell alterations occur rapidly within weeks to months after start of contact lens wear.
Contact lens induced bulbar conjunctival alterations (squamous metaplasia) are a likely cause of CLD
Eyen though such contact lens wearers with squamous metaplasia typically do not report symptoms at least within the first months after start of contact lens wear, such cellular alterations are conceivably related to adverse sensations compatible with what is termed as ´Contact Lens Discomfort´ (CLD) .
Squamous metaplasia was therefore identified a one likely reason for causing CLD during the TFOS CLD Workshop Report in 2013.
Further, frictional or possibly sub-clinical inflammatory impacts, associated with long-term contact lens wear may be responsible for an observed decrease (drop-out) of functional normal tissue of the Meibomian Glands with likely induction of MGD.
Silicone Contact Lenses with an increased stiffness (modulus) have an increased risk for causing epithelial slits (SEALs)
Contact lenses with high oxygen permeability and in particular silicone lenses have a certain tendency to induce corneal epithelial alterations such as´
- Superior Epithelial Arcuate Lesions´ (SEALs) that are epithelial erosions in the form of splits of the corneal epithelium often with irregular margins and with heaped-up cells at the margin. The occur in the superior part of the cornea, typically underneath the lid.
Generally, very thin Silicone Contact Lenses with an increased ´natural´ stiffness (modulus) have an increased risk for causing such epithelial. The risk is however only a few per cent of the users of such lenses and they are often asymptomatik, Still, they may be notices by the contact lens wearers as a unpleasant sensation that is subsummarized as Contat Lens Discomfort 8CLD)
Epithelial splits can also occasionally occur in conventional hydrogels without silicone. The risk for epithelial splits is therefore probably also related to the very thin lens design that may, even with a optimized geometry of the lens margin, pose a higher risk to ´cut´ into the epithelium.