Living Library

Contact Lens Associated Dry Eye

CLINICAL DESCRIPTION:
It is well established that an adequate and stable pre-corneal tear film (PCTF) is necessary to sustain contact lens (CL) wear 1-4.  In the presence of a CL, several changes occur to the PCTF and adnexa such as thinning of the PCTF, lipid layer disruption, increase in mucous secretions, changes in the blink characteristic and rate, and changes in lid conformity1. Corneal dessication, results due to the increase in tear evaporation, increase in tear osmolarity, decrease in tear break up time and increase in lysozyme and lactoferrin.  These changes are affected by the inherent properties of the CL material (perhaps lens dehydration) and the status of the PCTF prior to lens wear.  As a result of these changes, some patients experience dry eye symptoms associated with CL wear, hence referred to as CL-induced or CL-associated dry eye. 1-2
SYMPTOMS and OCULAR SIGNS:
CCLRU grading scaleCCLRU grading scale Symptoms1-7 of CL-associated dry eye include foreign body sensation, tearing or burning, ocular discomfort, red irritated eyes and a sensation of ocular surface dryness. Symptoms often worsen with the progression of the day and are exacerbated by drafts, air conditioning or heating vents, wind, tobacco smoke, chemical vapors, dust,  lint and other pollutants.
The ocular sign 1-2  most commonly associated with CL-induced dry eye is corneal staining. Varying degrees and extent of staining will indicate the severity of CL-induced dryness. Using a standardized grading scale, such as the CCLRU 8 grading scale (Figure 1), the progression and regression of the corneal staining can be monitored with more precision. With rigid gas permeable (RGP) lenses, the corneal staining is most often found at 3 and 9 o'clock, close to the limbus. With soft hydrogel lenses, the staining is most commonly found on the lower third of the corneal surface.
Other common signs 1-2 are lens surface dehydration, surface deposits, bulbar hyperemia and an increased conjunctival papillary response. 
INCIDENCE: 
It is challenging to find a consensus on the incidence and/or prevalence of contact lens induced dry eyes. This is due in part to the varying definitions of dry eye that exist in the literature coupled with the myriad of symptoms the patient describes and the numerous diagnostic tests available. In an effort to better compare future dry eye studies, a special National Eye Institute (NEI)/Industry Workshop on Clinical Trials of Dry Eye held in 1995 6   established a working definition of dry eye as;
Dry eye is a disorder of the tear film due to tear deficiency or excessive tear evaporation which causes damage to the interpalpebral ocular surface and is associated with symptoms of ocular discomfort.
This should standardize somewhat the definition of dry eyes and faciliate comparison and interpretation of international studies. Contact lens associated dry eye falls within the evaporative dry eye section of the above definition.
Depending on the methodology, age group and gender of those studied, dryness symptoms have been reported anywhere between 10-28% 4.  Surveys by Robboy and Orsborn9  indicate that dryness is the most common complaint and reason for discontinuation, up to 40%.  Doughty et al. 10 reported 28.7% of all CL wearers in Canada report dryness.  Other studies confirm that dryness increased by the end of the day 11-15 and that symptoms correlate well with ocular signs. Symptoms are more prevalent in females and in the elderly population. 5
ETIOLOGY:
The etiology of CL associated dry eye can be either one of two things; the alteration of the PCTF and/or the CL itself, that is its water content, lens material and lens thickness.
PCTF:
A marginally unstable or insufficient PCTF may become exacerbated in the presence of a CL. Identifying patients with this type of PCTF and other precursors can limit CL-associated dry eye and decrease chair time of unnecessary subsequent visits.
The McMonnies Dry Eye Questionnaire 16-17 has been designed to identify factors such as medication use, systemic and ocular surface disease, pre-existing symptoms of dryness and other factors which can lead to identifying marginally dry and potentially unstable PCTF. A comprehensive history is vital in identifying potential factors including environmental factors at home and at the workplace that places the CL candidate at risk for dryness.
A comprehensive anterior segment examination, with particular attention to the PCTF and lid margins, can often unmask numerous problems when dry eye is suspected. An evaluation of the PCTF’s production, distribution, outflow and stability as well as ocular surface structure integrity needs to be meticulously performed.
Production:
The lacrimal gland produces the majority of the aqueous layer of the PCTF, while the meibomian glands produce the outermost lipid layer. The Schirmer tear test 18 or the Phenol Red Cotton Thread Test (CTT) 19 will identify if production of the PCTF is sufficient. Table 1 identifies values that are indicative of an unstable or inadequate PCTF.
Digital expression of the meibomian glands should provide clear sebaceous fluid-like secretions indicative of a healthy lipid layer 20-21. The tear meniscus adjacent to the meibomian gland orifices can be observed to be slightly colored by the oily secretions. A colored PCTF throughout the ocular surface, without forced gland expression, is indicative of overactive sebaceous glands and will contribute to a sticky PCTF, attracting various debris.
Observation of the tear meniscus height 22-23 is an approximation of tear production. Usually the inferior meniscus is larger than the superior and approximately the same in both eyes (given that there are little anatomical differences between the two eyes). An inferior tear meniscus height less than 0.3 mm is suspect and is indicative of aqueous deficiency. 
Distribution:
Uniform distribution of the PCTF 1-2 is directly related to the action of the lids. Observation of the blink for completeness and lid-globe apposition is necessary for proper PCTF distribution. A loss of lid conformity due to scars, deformation or anomalies such as entropion or ectropion will disrupt the flow along the lid margin.
An abundance of debris along the tear meniscus will increase the viscosity and slow down the flow towards the punctum. Make-up and debris, from untreated blepharitis or other environmental debris, will contribute to a reduced flow and distribution.
Outflow:
A good apposition 1-2, 24 between the globe and an open punctum is necessary for proper outflow of the PCTF. The PCTF leaves the ocular surface via the nasolacrimal route. A positive Jones test 1-2 will reveal a fluorescein stained PCTF in the ipsilateral nostril indicating an unobstructed nasolacrimal route.
Stability:
In addition to evaluating PCTF production, distribution and outflow, it is equally important to evaluate PCTF stability 24. Although the tear break up time (TBUT) test is very variable, it still remains a clinically relevant and popular test of PCTF stability 24. Using a broad illumination beam and the appropriate excitation (Cobalt) and barrier (Yellow Wratten #12) filters should enhance visibility of the break. To further improve this technique, the Dry Eye Test (DET) was introduced in which the fluorescein strips are narrower and deliver a smaller amount of fluorescein to the PCTF. This methodology has improved the repeatability of the TBUT 5-6. Non-invasive tests of PCTF stability, such as tear thinning time (TTT) 25-26 and non-invasive break up time (NIBUT) 27 using the Tearscope 28 generally reveal longer tear rupture times. Table 1 indicates expected values of the PCTF stability.
Corneal and Conjunctival Integrity:
Following observation of the cornea and conjunctiva, the integrity of these structures is evaluated using vital stains such as fluorescein, rose bengal or lissamine green 29-30 . Fluorescein stains defects of the corneal epithelium and are best observed using a Cobalt excitatory filter coupled with a yellow Wratten barrier filter to maximize fluorescence. Rose bengal or lissamine green, used with white light, stains devitalized corneal and conjunctival cells as well as normal conjunctival mucus. Lissamine green is reported 31 to be gentler upon instillation as compared to rose bengal which is photosensitizing. Expected results of normal ocular surface structures with vital stains range from scant to no staining. Generally signs of dry eye are revealed as inferior and/or 3-9 o'clock corneal and conjunctival staining.
Laboratory Tests:
Many other tear film tests 1-2, 5   are available such as osmolarity, lactoferrin levels, and impression cytology of the conjunctival epithelium. However these require special instrumentation and technical knowledge that are not always available in, or conducive to, a  clinical setting.
CL Dehydration and Induced Dryness:
A hypothesis put forth by some authors 32 is that as the CL loses water while wearing the lens, the oxygen transmissibility of the lens is reduced, which in turn increases the hypoxic stress on the cornea and reduces its sensitivity.  Therefore, there is reduced reflex tearing and thus you have a dryer eye.  Also contributing to this process is the increased tear osmolarity which dehyrates the lens and the cornea resulting in a dryer lens/eye. 33
Still little is known about the effect of lens dehydration and its relationship to the symptom of dryness.  Conflicting results also exist, where a relationship was found by Efron and Brennan 34 and no relationship was found with studies by Pritchard and Fonn  35 and Fonn, Situ and Simpson. 36 
Lens Material:
Pusch and Walch 37  describe the differences between soft CL materials (unrelated to water content) but, varying with temperature.  CL’s containing methacrylic acid (MA) are composed of more free water molecules.  This wetting agent attracts more water and thus can release more water, readily when the lens goes from the container to the increased ocular temperature and then, throughout the day.  Whereas, lenses containing n-vinyl pyrrolidone (nPVP) are composed of more bounded water molecules.  The lens loses its ability to hydrate ions thus is limited in the amount of hydration energy which limits the amount of water loss i.e. less dehydration on eye.
It is unknown as of yet whether silicone hydrogel lenses have similar properties, related to the use of silicone and other components used to make the surface wettable.
We suspect RGP lenses, having mixtures of silicone and fluorine, that, it is the property of these materials to attract deposits (protein and lipid, respectively) that may more affect the dryness of the surface rather than the material itself.
Water Content:
Many studies have tried to relate water content to lens dehydration and symptoms of dryness.  The higher the water content, the greater the water loss from 11 to 15% with increased symptoms of dryness and the lower water content lenses dehydrated the least, from 2 to 6% with less symptoms of dryness. 38-40
On the other hand other studies by Pritchard and Fonn, 35 and Fonn, Situ et al 36 have not shown this relationship between dehydration and symptoms of dryness.  They allude to other causes for symptoms of dryness other than material or water content of the contact lens. 
Again, silicone hydrogel lenses have not been yet directly related to the performance of other lenses, but, we perhaps could imply that the lower water content of these lenses would perform similarly.
Material dehydration due to water loss is not an issue with RGP lenses having no water to lose.
Center Thickness:
Conflicting results have been reported regarding center thickness (CT).  Some have shown that there is a relationship between thickness and water loss 41 and others 42,43 reported no role of CT.  They found that thicker lenses had a slower dehydration rate initially but, reached the same equilibrium water content as the thinner lenses of the same water content.

MANAGEMENT

PCTF:
There is an intimate relationship between contact lenses and the PCTF, hence factors affecting one will have an influence on the other 3, 44-46 . Management of CL-associated dry eye will depend on the problem identified 1-4, 46. Factors identified during history such as medication use and systemic diseases need to be further considered for their potential effects on the PCTF. Medications 1-2, 46  often associated with reduced tear production include anti-histamines, tricyclic anti-depressants, beta-blockers, oral contraceptives and non-steroidal anti-inflammatory agents. An understanding of the work/leisure environment needs to also identify if a more ergonomic approach would avoid heating and air condition vents .
Any preexisting condition, such as blepharitis or Meibomian gland dysfunction (MGD) needs to be treated prior to CL wear. 
For production problems such as aqueous deficiency, tear substitutes (preferably non-preserved), inserts or punctal plugs can offer relief. An improvement of symptoms with trial dissolvable plugs can indicate if a more long term approach would be beneficial. For mucin deficiency, mast cell stabiliser can aid in the treatment of the tarsal plate as well as vitamin A drops 47 and hypotonic solutions. For severe cases  acetylcystine can be used for mucous strands. For lipid deficiency, hot compresses, lid scrubs, topical antibiotics can be useful to stimulate the sebacous glands. Systemic tetracycline may also be useful in severe cases.
For distribution problems such as incomplete blinks, the patient may be made aware of the problem and that in itself (with a post-it reminder at the work space) may induce more frequent blinking, however variable. Surgical intervention for lid scars and abnormalities should be considered if they cause a poor lid/globe apposition, especially around the punctum area.
For outflow problems, dilation and irrigation (D&I) procedures should eliminate any obstruction. Dilating a closed punctum and then irrigating the nasolacrymal route should restore a proper outflow. The Jones test #2 (following a D&I) should show fluorescein in the ipsilateral nostril. 
Stability problems, caused by blepharitis, MGD or excessive make-up debris should be treated with proper lid hygeine (daily lid scrubs, warm compresses) to improve the quality and hence the stability of the PCTF. Addressing the production problems mentioned above will also contribute to an increased stability of the PCTF, as documented by an increased rupture time.
In order to compare clinical studies, it is recommended that standardized documentation be used. Corneal staining caused by dryness can be documented using the standardized CCLRU grading scale 8 and tracked for progression and/or regression with better precision. Improvement is expected as causative factors are eliminated or controlled, hence an improvement of corneal staining should be evident.
Contact lenses Options:
Lens Material. Change lens material, if ionic go to non-ionic, that is, increase the material wettablility by adding n-vinyl pyrrolidone (nPVP) instead of methacrylic acid (MA) or visaversa.  Try a combination lens (omafilcon A) that has properties of a Group 2 material, such as the Proclear lens, which recently received FDA approval as a material for the dry eye patient. 48-50 
Water Content:
Change the water content, if high go lower or visaversa.
Center Thickness:
Try a slightly thicker lens, but, do not compromise oxygen transmission.
Overall, going to a more frequent replacement schedule of any lens will reduce the incidence of deposits which contribute to the feeling of dryness.  Take into consideration the solutions the patient is using, perhaps a non-preserved system would prevent preservative-deposit binding that contributes to dryness and inflammation.
In severe cases, a reduced wearing schedule of daily replaced lenses would be ideal. If optically viable, going to an RGP with a low amount of silicone content could also be considered.
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Cornea and Contact Lens Living Library
Contact Lens Associated Dry Eye
Edited by:
Etty Bitton O.D., MSc., F.A.A.O., University of Montreal   
School of Optometry
Luigina Sorbara, O.D., MSc., F.A.A.O., University of Waterloo School of Optometry