Contact lens part 3: the ocular surface in contact lens wear: course code C-13462.
Solving symptomatic problems of a contact lens wearer often forms the primary focus of patient aftercare and management. However observing the mechanical and physiological impact of contact lenses on the ocular surface also forms a fundamental part of the management of our contact lens patients Not only is it important to observe the cornea, but also the conjunctiva and eyelids. This article reviews the current understanding of some of the most frequently seen responses of the ocular surface to contact lens wear and the recommended methods for their examination and observation.
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Grading the appearance of the ocular surface
Slit-lamp biomicroscope examination of the anterior eye and adnexa is integral in contact lens practice for eye care practitioners, and an important part of such examination is to assess the ocular surface for signs of mechanical or physiological irritation, such as staining, redness and swelling. Grading our observations with accuracy and repeatability is particularly important for ongoing patient management and to establish evidence of improvement or deterioration. Most UK practitioners will be familiar with clinical grading scales. These are generally photographic eg the Cornea and Contact Lens Research Unit (CCLRU) scale, (1) or pictorial eg the Efron scale (2) (Figure 1). Today's eye care practitioners should certainly be using a suitable grading scale in practice as it has been shown to be superior to traditional verbal descriptors in terms of reliability and repeatability. (3) This is particularly important in a practice where several practitioners work together and may see each other's patients; having a grading scale readily available within each consulting room is vital, but it must be the same scale since cross-comparisons cannot otherwise be made. (4)
What is perhaps less well-known is the importance of interpolation of grading scores between the discrete integer intervals that are provided on the scale. The CCLRU and Efron scales are based on a zero to four scale, where '4' represents the most severe anchor. By grading to decimal places that are representative of points in between two successive integer points on the scale, e.g. 1.3, 2.4, 3.5 etc., the scale is expanded and the sensitivity (ability of the scale to discriminate a difference) is thereby increased. (5) However, there is a limit to such interpolation; 0.1 increments are generally considered optimal as any finer intervals would promote poor concordance between observers. (4,5)
The variability of grading scores between practitioners can be wide and they generally tend to form clusters around whole numbers. (6) However, evidence suggests that this tends to improve with training or practice. (4,7-10) One criticism of grading scales is that they may not necessarily cover all possible clinical appearances, (11) particularly at the severe end of the scale, and that they may not be linear. (5,12) Objective analysis of digital images provides an attractive alternative to the subjective nature of practitioner grading, and this has the potential to be more sensitive. (10) However, the subjective judgement that a practitioner makes at the slit lamp is actually a complex one to mimic objectively. For example, the grading of ocular redness objectively involves judgement of both the hue and vessel size, relative to the area under question. Approaches to this challenge are still emerging (13) and further development in this area is anticipated. One interesting development is the use of 'morphing' grading scales, which are accessible digitally within the consulting room either on disc or via customised software (Figure 2), which can be used to show gradual changes from one grade to another by manipulation of a slider.
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Normal grading scores for the ocular surface
There is a general inference that the first grade on the scale (zero or 1, depending on the scale used) represents the normal, non-contact lens wearing eye, but close examination of the grading scale guidelines and evidence from research suggest otherwise. For example, the CCLRU grading scale states that in general, a grade of slight (grade 2) or less is considered within normal limits. Studies have shown that the normal ocular appearance is not necessarily the lowest level on the grading scale, nor is the 'normal' level the same score for each appearance, ie the scales may not be 'aligned'. This does not devalue the use of the scales in clinical practice, but it is important that eye care practitioners have an idea of these 'normal' values for the appearance of the ocular surface, so that we might correctly interpret findings in our contact lens patients.
Table 1 presents the normative values (according to the scale used) for the most pertinent features of the ocular surface for contact lens practice.
Use of fluorescein staining in contact lens wearers
Some degree of corneal staining is found in up to 79% of corneas (9) and 71% of conjunctivas (16) in healthy, non-contact lens wearing individuals, so some corneal staining could result directly from the normal physiological process of desquamation at the surface (supported by the fact that it varies from day to day (16)). However, signs of corneal staining could also tell us that the cornea is compromised. Interestingly, although sodium fluorescein (a pH indicator dye) has been widely used to assess corneal integrity since the 19th century, it is still not absolutely clear how it acts on the ocular surface. (16) It is commonly accepted that it penetrates only interruptions or gaps in the epithelium and therefore only via damaged cells can it permeate into intracellular spaces and possibly underlying tissues. (17) However, there is some evidence to suggest that cells do not have to be damaged to be stained by fluorescein. (16,18)
The natural ability of sodium fluorescein to fuoresce at 510-520nm under exposure to light of wavelength 495nm (visible blue), (19) allows excellent visualisation of the dye in the eye, but not all slit lamps seem to provide this exact optimal wavelength of light. (20) Viewing of this fluorescence is further enhanced by using a yellow barrier filter, since this absorbs any reflected, superfluous blue light (Figure 3). However, practitioners should also be aware that yellow filters could also vary in their ability to match the optimal absorption wavelength. Yellow barrier filters can be hand-held (see figure 12) or be built into the slit lamp; you can also utilise the Fluorescein setting on your fundus camera (in 'anterior eye' mode) to good effect, as there will be a built-in barrier filter. (21)
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Most practitioners would admit to using a 'moisten and shake' approach with a Fluoret and in fact this represents a valid technique. It has been shown that moistening a Fluoret strip with saline and shaking the excess off, or using a drop from a Minim of 1% Fluorescein, will reach a useful level of fluorescence much faster, and will also last sufficiently long enough to be useful, compared to not shaking the Fluoret, or using 2% in a Minim. (20) Indeed, Fluorescein has a natural limit to its intensity of fluorescence such that at high concentrations, the fluorescence diminishes; this is termed 'quenching'.
When fluorescein is first applied to the eye, it appears yellow under normal white illumination but as it rapidly dilutes in the tear film, its characteristic green appearance becomes visible. (19) This is why it is best to wait at least one minute before examining the ocular surface after fluorescein instillation.
Practitioners tend to vary in where they apply a moistened Fluoret--for examination of the fit of gas permeable contact lenses, superior bulbar application may be preferred to introduce the dye behind the lens with the first blink, but for general use, applying the moistened Fluoret to the inferior tarsal plate avoids any potential unintentional conjunctival staining. (19) Practitioners should be aware that several instillations of Fluorescein during a consultation will increase the amount of corneal staining observed, although the reasons why are unclear. (22)
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A recent survey (23) recorded that only 75% of UK eye care practitioners claim to use fluorescein at most appointments, despite UK professional guidelines highlighting the need to use such diagnostic agents routinely in contact lens practice. Reasons cited for not using fluorescein routinely include subsequent discolouration of hydrogel lenses and concerns about Pseudomonas aeruginosa infection following instillation. Now that the majority of patients wear disposable contact lenses, discolouration is less of a worry whilst concerns about Pseudomonas aeruginosa are actually founded on an incidence in the 1950s with non-preserved sodium fiuorescein solutions in a hospital clinic; the more commonly used sterile strips fail to colonise with the organism even with deliberate contamination, and therefore pose much less of a risk. (23)
Fluorescein staining patterns in contact lens patients don't always match their symptoms. Careful grading and recording is important here to help to understand the aetiology, and one recommended technique is to segregate the cornea into five separate zones and then to apply your grading scale of choice to each zone (Figure 4).
Contact lenses and corneal staining
The cornea is a self-renewing tissue, with stem cells located at the limbus that begin the process of cell proliferation at the basal cell layer of the limbus and corneal epithelium. As cells develop, they move upwards/anteriorly to be eventually shed into the tear film (desquamation). Contact lens wear alters both surface cell exfoliation and proliferation in the corneal and limbal epithelia--a decrease in the number of exfoliating cells is observed with both daily and overnight wear. (24,25) Indeed, the effects of eyelid closure and wearing of any type of contact lens appears to slow down these processes, (26) so we might expect to see an increase in corneal staining.
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Begley and colleagues (27) observed that one-third of hydrogel contact lens wearers had significant corneal staining, but the average grade amongst asymptomatic wearers was 0.5. Temporal and nasal grades tended to be similar but lower than superior and inferior grades. The prevalence of any degree of corneal staining amongst contact lens wearers is about 60%, (28) but values in the literature vary due to different definitions of 'significant' grading.
The clinical appearances of corneal staining in contact lens wear are well described in text books (29) but certain types are characteristic of common problems. A superior epithelial arcuate lesion (SEAL) is frequently associated with poorly fitting lenses, particularly if they have a high modulus (Figure 5). Desiccation staining on the peripheral cornea of a rigid gas permeable (RGP) contact lens wearer is known as '3&9 o'clock' staining, and is frequently associated with poor blinking in such patients (30) (Figure 6). Desiccation staining on the inferior cornea of a soft lens wearer is known as 'smile' staining (Figure 7) whilst solution staining may be diffuse or annular with central sparing (Figure 8). Dimple veiling is the name given to staining of indentations that represent bubbles of air in a stagnant tear film usually behind a steep fitting RGP lens (Figure 9).
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Visual acuity (VA) is generally not affected by corneal staining unless it is severe and coalesced. It should be remembered that the correlation with discomfort is frequently weak--foreign body staining can be superficial but very painful, and conversely, a patient with diffuse and extensive punctate staining may have no symptoms at all. The cornea generally recovers very quickly once the cause of the staining is removed; superficial staining will disappear overnight, whereas deeper or more extensive staining needs supervision over the following days to check corneal integrity, before resuming lens wear.
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Use of lissamine green in contact lens wearers
Whilst fluorescein is very good at staining compromised cells and their boundaries, particularly on the cornea, its counterpart in ophthalmology for almost 80 years has been rose bengal (RB), which stains dead or degenerate cells and mucous, or healthy cells unprotected by mucous. However, RB has a rather vicious sting for patients and is seldom used in optometry. Lissamine green (LG) has similar staining characteristics to RB, (31) but stings very little in most patients and is experiencing something of a resurgence in popularity of late, after being introduced originally as a food dye in the 1970s. It is available in paper strips impregnated with 1.5mg of the dye (Figure 10). The recommended technique is to apply two large drops (10-20[micro]l) of the dye from the strip into the lower fornix, one eye at a time, and to wait for at least two minutes to observe any staining. (32) Any pooled dye must dissipate before viewing the staining. Staining can be punctate or coalesced and you should observe this with reduced white light or with a red barrier filter (transmits 634-567nm) to improve visibility (available from www.ocular-solutions.co.uk or from the Vision Care Institute of Johnson & Johnson; Figure 12). Interestingly, there is an emerging trend in using 'double staining'--applying a combined application of both dyes. It has been shown that a mixture of 2% fluorescein and 1% LG can aid simultaneous observation of corneal and conjunctival staining, (33) but this author prefers to observe tear film stability, then fluorescein staining followed by LG staining as separate procedures. This avoids any staining of mucous by LG, which may affect subsequent tear film stability assessment. Recording LG staining of the conjunctiva should be done in at least three zones: nasal, temporal and corneal, (34) but with contact lenses it can also be useful to examine the inferior and superior regions, by lifting the lids slightly. Assigning a score to the LG staining observed can be done using the Oxford grading scale (34) (Figure 13), which has a series of panels reproducing the staining patterns met with in dry eye patients. Typically, nasal LG staining is greater than temporal LG staining in non-lens wearers. Corneal staining with LG is rare except in cases of severe dry eyes and it can be difficult to see due to the lack of contrast. Rather, it is the ability of LG to stain the conjunctiva and the lid margins that is of particular importance in contact lens practice.
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Contact lenses and the conjunctiva
When fluorescein is instilled it naturally collects in the 'furrows' of the normal adult bulbar conjunctiva (Figure 14), and it is only when this sign remains after more than a few minutes that it can be associated with desiccation. Conjunctival staining can be an early sign of dryness problems on the ocular surface, even without any corneal staining, (35) and will persist in chronic cases alongside subsequent corneal staining. At a cellular level, contact lens wear appears related to reduced cell density in the conjunctival epithelium, and mild thinning. (36) In contact lens wearers particularly, conjunctival staining may occur before corneal staining because the cornea is 'protected' somewhat by the lens itself (Figure 15). One aspect of conjunctival assessment in contact lens wearers that does not require any staining agent for examination is that of lid-parallel conjunctival folds or LIPCOF. LIPCOF are sub-clinical folds in the lower conjunctiva parallel to the lower lid margin (Figure 16), that have been shown to be strongly predictive of symptoms in contact lens wearers. (37,38) LIPCOF are evaluated using a 2-3mm vertical slit at 25x magnification, with narrow observation angle. The area to be observed is below the horizontal limbal area at the lower lid margin--the number of folds and the height of them can be classified according to a four-point grading system (Table 2). Friction between the upper eyelid and the bulbar conjunctiva is thought to interfere with lymphatic flow, resulting in dilation and ultimately folds.
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Contact lenses and the eyelids lid wiper epitheliopathy
The contacting edge of the upper eyelid on the ocular surface is termed the 'lid wiper'. Lid wiper epitheliopathy (LWE) is a clinically observable alteration of the epithelium of the wiper area. LG is useful to stain this area (Figure 17) since in contact lens wearers with dryness symptoms, increased friction causes cell loss in this area. According to Korb et al, (39) 80% of contact lens wearers who suffer from dry eye display staining of the lid wiper versus only 13% of asymptomatic lens wearers.
Contact lens wearers with dryness symptoms have been shown to exhibit significantly more LWE and LIPCOF, but not necessarily increased corneal staining, bulbar hyperaemia or decreased tear film stability, compared to asymptomatic wearers. The correlations between LWE and LIPCOF are significant; this may reflect their common frictional origin. (38)
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Meibomian gland dysfunction (MGD)
The potential for contact lens wear to influence meibomian gland changes is controversial, with conflicting evidence in the literature. This may reflect differing methodologies; the most recent evidence suggests that contact lens wear is associated with a decrease in the number of functional meibomian glands that is proportional to the duration of lens wear, and there is no significant difference between RGP and hydrogel lens wearers. (40) Contact lens wear appears to produce similar effects on the dropout of glands to that seen with aging, (40) and more effect on gland shortening and drop-out is seen in the upper lid compared to the lower lid. (40) This supports the idea that chronic irritation through the conjunctiva is the cause, (41) although it has also been suggested that dead epithelial cells may actually block the orifices. (42) Increased redness at the lid margins is perhaps a sign that does not receive enough attention, but is indeed associated with MGD (Figure 18).
Ocular redness in contact lens wear
It is usually considered that soft lens wearers tend to exhibit more limbal injection than RGP lens wearers, (7,44) but several studies have now shown a decrease in limbal hyperaemia with the latest high Dk silicone hydrogel lenses, a direct correlation between oxygen permeability and physiological performance. (46-50) In extended wear, it has been shown that the vascular response is less (48,50) and quicker to recover[w] in subjects wearing high oxygen permeability lenses compared to low oxygen permeability lenses.
It is important to remember that the painful red eye normally requires urgent attention. Redness will not usually provoke pain or severe discomfort--corneal involvement is indicated in patients who present with pain, and practitioners must make careful assessment. One of the more fundamental clues to management of redness in a contact lens wearer is whether the problem is bilateral or unilateral. Bilateral redness suggests a systemic, or solution problem. Unilateral redness is much more likely to reflect a specific problem with that lens or eye, such as infiltrates, damaged lens, conjunctivitis, or keratitis etc.
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Examination of bulbar redness is best achieved directly with a broad white beam, whereas the limbal arcades are easier to see in retro-illumination and using higher magnification. Blanching of blood vessels around lens edges indicates direct compression of the vessels due to a tight fitting lens (Figure 20).
The assessment of redness and staining on the ocular surface are such fundamental parts of our slit lamp routine that it is worth reviewing the current knowledge. This article has highlighted the typical changes in redness and staining of the ocular surface that may be seen in our contact lens patients, and reviewed the current recommended methods for examination. A future series of articles in Optometry Today will deal specifically with the management and treatment of the types of problems described in this article.
Course code- C-13462
1. Where should you observe lid-parallel conjunctival folds (LIPCOF)?
a) Parallel with the nasal limbus
b) Parallel with the temporal limbus
c) Parallel with the lower lid margin
d) Parallel with the upper lid margin
2. Which wavelength of light is optimum for illuminating sodium fluorescein?
3. Why should you grade between the main intervals on any grading scale?
a) It improves reliability
b) It improves sensitivity
c) It improves specificity
d) All of the above
4. How does a yellow barrier filter aid the viewing of a rigid gas permeable (RGP) contact lens fit with sodium fluorescein?
a) It reflects unwanted blue light
b) It absorbs any reflected blue light from the ocular surface
c) It enhances contrast by reducing illumination
d) The wavelength of the filter is the same as the light source
5. A Grade 3 lid-parallel conjunctival folds (LIPCOF) score describes the appearance as:
a) 2 folds of height 0.1 mm
b) 1 fold
c) 3 folds
d) Several folds of >0.2mm
6. What causes the phenomenon of "quenching"?
a) The fluorescein dilutes too quickly
b) Too much fluorescein causes a decrease in fluorescence
c) Not enough fluorescein has been applied
d) Altered pH in the tear film
7. What affects on the meibomian glands might you see in a contact lens wearer with dry eye symptoms?
a) Lid margin redness
b) Meibomian gland drop-out
c) Meibomian gland blockages
d) All of the above
8. What type of staining is frequently associated with stagnant tears?
a) Arcuate lesion in the inferior cornea
b) Dimple veiling
c) Smile staining
d) Arcuate lesion in the superior cornea
9. What Cornea and Contact Lens Research Unit (CCLRU) grade of Iimbal hyperaemia represents an upper limit for normal eyes?
10. Which of the following is the most likely cause of lid wiper epitheliopathy?
a) Friction between the conjunctiva and the tarsal plate
b) Inflammation of the meibomian glands
c) Friction between the inner lid margin and the ocular surface
d) Inflammation of the bulbar conjunctiva
11. Lissamine green acts on which components of the ocular surface?
a) Dead cells and mucous
b) Healthy cells and lipid
c) Dead cells and lipid
d) Healthy cells and mucous
12. In which region of the bulbar conjunctiva would you expect to see most lissamine green staining in a non-contact lens wearer?
Dr Christine Purslow PhD MCOptom, FBCLA, FIACLE
Dr Christine Purslow is a lecturer in the School of Optometry & Vision Sciences, and a director of the Contact Lens & Anterior Eye Research (CLAER) Unit at Cardiff University. She is also a member of the College of Optometrists, and a Fellow of both the BCLA and the International Association of Contact Lens Educators (IACLE).
Table 1 Typical grading scores for normal, non-contact lens wearers. NaFL = Sodium Fluorescein, LG = Lissamine Green UPPER MEAN (MEDIAN) LIMIT OF SCORE for non- NORMALITY FEATURE GRADING SCALE CL wearers Bulbar McMonnies 0.9 2.3 redness (14,15,44) (0-5 photos) CCLRU 2.0 3.0 CCLRU 1.9 2.6 Limbal redness (14) CCLRU 1.6 2.5 Corneal staining CCLRU (0.1) 0.5 (NaFI) (9) Conjunctival Oxford 0.3/0.8 1.4/2.4 staining (LG; grading temp/nasal) scale Upper palpebral CCLRU (1.3) 2.0 redness (8) Upper palpebral CCLRU (1.3) 12.0 roughness (8) Significant grade change FEATURE Bulbar [greater than or equal to] 1.0 unit redness (14,15,44) [greater than or equal to] 0.6 units [greater than or equal to] 0.4 units Limbal redness (14) [greater than or equal to] 0.6 units Corneal staining [greater than or equal to] 0.3 units (NaFI) (9) Conjunctival [greater than or equal to] 1.1/1.6 units staining (LG; temp/nasal) Upper palpebral [greater than or equal to] 0.5 units redness (8) Upper palpebral [greater than or equal to] 0.5 units roughness (8) Table 2 Lid-parallel conjunctival folds (LIPCOF) grading Grade 0 No parallel fold Grade 1 1 parallel fold Grade 2 2 parallel folds with a height of <0.2mm Grade 3 Several parallel folds with a height of >0.2mm
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|Title Annotation:||CONTINUING EDUCATION & TRAINING|
|Date:||Mar 26, 2010|
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