Non-invasive tearscope plus routine for contact lens fitting

Contact Lens and Anterior Eye, (Supplement) 21, pp. $31-$40, 1998 1998 British Contact Lens Association Printed in Great Britain

NON-INVASIVE TEARSCOPE PLUS ROUTINE FOR CONTACT LENS FITTING

Jean-Pierre Guillon *

Abstract - - The Keeler Tearscope Plus was invented by the author as a multi-use instrument for the non-invasive examination of the tear film, its appearance, volume, stability and, its effect on the ocular and contact lens surface. Its use is maximised by following a step-

by-step approach described which is based on simple clinical principles of tear film stability.

KEY WORDS: Keeler Tearscope Plus, tears, pre-ocular tear film, pre-lens tear film

Principle of Tear Film Stability

T he tear film has been described as a trilaminar structure (Figure 1) with different levels of com- plexity? -:~ Each layer plays a different role towards the formation and stability of the structure. The quality and quantity of each layer is important as well as their interfacial relationship. The pre-ocular and pre-lens tear film rely also on the separation of their component layers to provide a prolonged stability and thus an adequate protection over the surface it covers (Figure 2). Each component layer must be present in adequate quantity and present qualitative characteristics that permit the normal formation of a tear film during the distribution phase occurring with the blink. This distribution mechanism needs to be efficient and repeated at regular intervals at least shorter than the time taken for a dry spot to occur.

Layer Characteristics, Separating and Distribution An ideal tear film over a perfect corneal or contact

lens surface exists when each of its layers presents the ideal qualitative and quantitative characteristics. The lipid layer limits evaporation, the aqueous phase provides the main fluid bulk and secretion from the epithelial cells provides an anchorage over which the surface active mucous layer can spread and protect the ocular surface/

The film will stay stable as long as an adequate separation exists between the layers.

The distribution of the film is provided by the sweeping motion of the upper lid during the blink. As 75-90'% of the tear volume is found in the tear reservoir along the lids, 5 the upper and lower lid edges needs to come in contact for the resurfacing of the mucous, aqueous and lipid layer to be effective.

When such a blink is repeated at regular intervals, a structure of prolonged stability is created and an adequate protection is provided over the surface it covers.

*BSc., PhD, FCOptom.

The ocular surface, free from aggression will not give rise to symptoms of dryness ~ and the lens surface will be free from an accelerated deposition process but provides prolonged and comfortable wear.

Figure 1

PRINCIPLE OF TEAR FILM STABILITY [

POTF LIPID

AQUEOUS MUCOUS

OCULAR SURFACE

GOOD QUALITY GOOD QUANTITY

GOOD DISTRIBUTION

I

PLTF L~m

AQUEOUS MUCOUS

BLINKING

] l GOOD QUAL1TY I I CO TA :::NS I I

SEPARATION OF THE COMPONENT LAYERS

I GOOD STABILITY

GOODPROTECTION [ [ GOOD SYMPTOMS

Figure 2

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JEAN-PIERRE GUILLON

DESTABILISATION PRINCIPLE ]

I INCREASED SEPARATION

OF LAYERS

I

I

TEAR FILM

DETERIORATION OF

COMPONENT LAYERS

CONTACT BETWEEN

COMPONENT LAYERS

I PROTECTION I BAD

SYSTEM PROTECTION

l I SYMP'!'OMS

Figure 3

I PATHOLOGY

I LNCREASED

INTERACTION BETWEEN LAYERS

I

I I I "RO : :'ONI

Principle ofDestabilisation oftheTear Film (Figure 3) When one or more of the component layers of the

tear film is less than ideal, the separation between the layers is compromised and a localised thinning of the tear film occurs.

Two mechanisms have been put forward to explain this thinning. Holly postulated from surface chem- istry of thin films that it is caused by migration of lipids from the superficial layer towards the mucous phasC and McDonald s deduced from clinical observations that it is driven by aqueous flow towards the meniscus shaped tear reservoirs.

Tile current evidence 9,1 suggests that a multiplicity of factors causes the break and that evaporation due to non-continuous lipid coverage may be an aggravat- ing factor ~l that may also increase the hyperosmolar- ity of the tear fluid found in most dry eye cases? 2,13

The break occurs when either the air surface or part of the superficial lipid layer comes into contact with the basal mucous layer, and creates a dry or non- wetting spot.

Recently ~4 it has been demonstrated that in some pathological cases, the break occurs over an ex- tended area immediately following the blink and that the area of the break is recovered by a lipid phase rendering it non-wettable by aqueous tears and actively pushing it away. The damage caused to the ocular surface may further destabilise the structure by not supporting a functionally adequate mucous coverage (Figure 4).

The worst case exists when a large quantity of lipid comes into contact with the mucous layer and produce an active non-wetting area. This may be more common when abnormalities of the lipid layer are present as in blepharitis, when skin lipids invade the ocular area ~5 but also has been observed following the use of oil based cosmetic products? ~

PATHOLOGICAL DRY EYE I BREAK UP MECHANISM

CONTACT BETWEEN TEAR FILM LAYERS

LIPID PROTECTION SURFACE DAMAGE ~_~

I TII1N

AQUEOUS I--~-.J NON WETTING PHASE AREAS

I DECREASED

MUCOUS COVERAGE LIPID COATING

Figure 4

. . . . AA~TION

In cases of reduced aqueous production, the thin aqueous phase may also accelerate the interaction between the bordering layers. The longer the dry spot exists, the larger the area involved and the greater the effect on the underlying surface.

On the ocular surface cell necrosis will occur. On the contact lens surface increased evaporation and deposition will result in dryness-related symptoms.

Protection Mechanism of the Cornea (Figure 3) Protection of the ocular surface is effective when the

resurfacing process takes place before the creation of the dry spot.

When this is not the case, the protection system relies on the presence of symptoms to trigger a reflex blink.

In the marginal symptomatic dry eye, the blink may occur immediately following the break and the ocular surface may not show any deterioration but symptoms may be present especially if a hypertonic film exists.

In the case of more severe dryness, when a delay exists between the break and the blink, 17 the unprotected epithelial cells of the cornea and conjunctiva are damaged. The longer the delay, the greater the damage inflicted to the epithelial cells (leading to the appearance of staining following fluorescein, Rose Bengal or Lissamine Green instillation).

A damaged ocular surface commonly presents a reduced sensitivity whereby the early signs of irritation do not act as a trigger for the blink reflex which is delayed and only activated when further damage has been caused.

Principle of Non-invasive Examination with the Tearscope Plus The Tearscope Plus and its flexible inserts permits the visualisation of the superficial structures of the tear film, of the morphology of the tear reservoirs (regularity, height and curvature) and the non-invasive measurement of the stability by two different techniques. The

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NON- INVASIVE TEARSCOPE PLUS ROUTINE FOR CONTACT LENS F ITT ING

following list details the specific observations, grading and measurement of the pre-ocular tear film (POTF) and pre-lens tear film (PLTF) which can be achieved with the Tearscope Plus and be part of the routine examination of the prospective of current lens wearer (Figure 5).

The examination of the POFT comprises five parts: Observation and grading of the lipid layer Observation and grading of the tear reservoirs Observation of the blink sequence Measurement of the non-invasive break-up time Assessment of Meibomian gland blockage

The examination of the PLTF comprises four parts: Observation and grading of the lipid layer Observation and grading of the aqueous phase Observation and grading of the tear reservoirs Measurement of the non-invasive break-up time.

Examination of the POTF

Observation and Grading of the Lipid Layer (Figure 6) The grading of the lipid layer appearance in its undisturbed state should always be the first clinical observation to be made and as it is the most unstable structure it should not last more than 20 s per eye (with practice 10 s should suffice).11,16,18,19,

TEARSCOPE PLUS ROUTINE EXAMINATION FOR CONTACT LENS FITTING

POTF ]

OBSERVATION AND GRADING OF THE LIPID LAYER. OBSERVATION AND GRADING OF THE TEAR RESERVOIRS OBSERVATION OF THE BLINK SEQUENCE, MEASUREMENT OF THE NON INVASIVE BREAK UP TIME. ASSESSMENT OF MEIBOMIAN GLAND BLOCKAGE

I PLTF I OBSERVATION AND GRADING OF THE LIPID LAYER. OBSERVATION AND GRADING OF THE AQUEOUS PHASE = OBSERVATION AND GRADING OF THE TEAR RESERVOIRS MEASUREMENT OF THE NON INVASIVE BREAK UP TIME.

Figure 5

Figure 6

The practitioner needs to recognise the pattern linked to the most stable tear film (amorphous) as it represents the best candidate for comfortable contact lens wear, those linked to increased evaporation and reduced stability; (Break-up, Abnormal colours, Globu- lar), the normal pattern linked to average stability; (closed meshwork, wave and normal colours and the pattern of thin coverage that may not form continuously over a contact lens; (open meshwork).

Stable lipid layer (amorphous) The even reflective surface of that layer represent a well mixed structure of around 80 nm thickness.

Unstable lipid layer: (Break-up Pattern) When the lipid layer is not continuous, a fourfold increase in evaporation has been measured. 11 This is most common when a source of contamination of the lipid layer exists. When a surface active substance finds it way to the surface of the tear film it may have the ability to break the lipid layer and in the worst cases confines it temporarily to a very small surface area. The area of an abnormally thin lipid layer appears as a darker zone of reduced reflectivity, 2 and full breaks are seen as a non-uniform surface representing the bare aqueous surface where full destructive interference of the Tearscope illuminating source exists.

Possible contaminants are sebum skin lipids but most likely they are of cosmetic origin in a young female population which represents 70% of contact lens wearers. 21 The worst culprits are oily make-up removers, night creams, mascaras. Close attention must be paid to the use of these cosmetic products as they will create localised instability at the contact lens surface in the areas close to the lid border and tear meniscus.

Unstable lipid layer: (Globular or Abnormal colours) When the lipid layer presents an abnormal colour pattern (colours of the second and third order of interference) which can become globular it is most likely linked to the presence of abnormal Meibomian secretion with poor spreading ability and a high melting point. The evaporation rate is usually high and the stability low. In these case lid hygiene treatment with hot compresses and Meibomian gland manipulation should be started before or at the earliest stage of fitting to avoid lens surface contamination and accelerated contact lens deposit formation.

Thin lipid layer: (Open Meshwork Pattern) This pattern is so thin that it is usually only seen at low magnification with the Tearscope Plus by its upward movement following the blink and is not visible a few seconds later. All previous research work has demonstrated that the PLTF is always more unstable than the POTF and that is usually supports a thinner lipid layer. If an extremely thin lipid layer exists at the surface of the POTF it is most likely that very poor or absent lipid coverage will be present at the surface of the PLTF. Potential wearers should be warned of the possibility of

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JEAN-PIERRE GUILLON

increased evaporation problems and evaporation resis- tant material could be considered at this stage as well as the use of re-wetting drops.

Normal lipid layer: (Closed meshwork, Wave, Normal Colours) These patterns represent the most common lipid appearance and are linked to average tear film stability. Multiple pattern lipid layer

Sometimes the lipid layer pattern following a blink cannot be classified as single appearance but may present two or more patterns within the corneal surface area.

Zonal distribution It is quite common for the lipid layer to be thicker in the lower area and thinner near the upper lid (as if the upper movement of the lid did not drag the layer in a uniform fashion but thins towards the top). In this case if the different components appear normal and well spread within their own horizontal zone, we are in the presence of normal secretion but uneven distribution and it will be most important to inspect the area along the upper lid for the presence of meniscus-related thinning or break of the PLTF. The repeated lack of lipid coverage in a localised area may cause the process of tocalised pervaporation and induced epithelial staining. 22

Irregular mixing of lipids If the lipid layer presents a pattern of multiple appearance representing various lipid thicknesses, this may be due to the presence of lipid secretions of different composition and melting points and is a sign of meibomian gland abnormality. When contact lens fitting is considered, adequate treatment, explained previously, should be applied.

Presence of contaminants The lipid layer may present irregularities at its surface. Most commonly spot like particles from dust or cellular debris have little effects, but irregular floating features visible as a change in reflectivity of the layer (either fainter or brighter) denote a localised thickness difference and can be described as plaque (when it appears darker and thinner than the surroundings) or oil (when it appears brighter and thicker than the surroundings).23,24

over the corneal or the conjunctival surface creating instability and symptoms of dryness. Tear reservoir morphology

When viewed with the Tearscope Plus, the reservoir presents a central black zone bordered on each side by areas of bright white reflections (Figure 9). The

CO

Figure 7

Figure 8

Observation of the Tear Reservoirs (Figures 7 and 8) The morphology of the tear reservoir has been shown to influence the stability of the tear film. It can be visualised with the Tearscope Plus along with the whole lid margin and graded for height, regularity and continuity. By examining its morphology the practitioner can assess the amount of tear fluid available for the formation of the pre-ocular tear film by the spreading action of the lids during the blink. A full tear reservoir present along the whole length of the lid represents a favourable situation for normal tear film formation. A reduced volume, an irregular or a non continuous reservior are all signs of unfavourable conditions that may lead to poorer tear film formation Figure 9

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NON-INVASWE TEARSCOPE PLUS ROUTINE FOR CONTACT LENS FITTING

observation of those three zones and their regularity permits a quantitative and qualitative assessment of the reservoir over its entire length (Figure 10). The tear reservoir is bordered on the lid side by the muco-cutaneous junction which is hydrophobic due to the nature of the sebum coating provided by the skin lipids. On the tear film side, an area of thinning produced during the blink phase by the mechanism of fluid attraction stops all fluid exchange between the reservoir and the tear film within 2 - 3 s from the completion of the blink.

Full reservoir A full reservoir with ample supply of fluid will present a thick regular central black band and the height of the striped structure will be a measure of the volume available.

Blocked Meibomian glands (Figure 11) In the presence of any Meibomian gland blockage, the gland opening is coated with Meibomian secretion and the aqueous phase of the tear film is dragged under- neath the coating. When the blockage is present over successive gland openings, a deformation of the tear reservoir occurs as it is pushed away between the gland by the lid coated with sebum and pulled forward at the site of the gland opening. This deformation produces a distortion of the central black zone which points to each individual gland opening which are blocked. Such an appearance will warrant the examination of the glands by translucence through the palpebral conjunctiva and the need to do a gland efficiency test (see next paragraph).

Displaced reservoir The reservoir is usually regular when it forms over the corneal surface. In cases of large palpebral apertures it may form over the conjunctiva which has limited regularity and its shape might be flattened reducing the volume available. Combined with a larger exposed area this may be the cause of increased instability and exposure dryness symptoms. Reservoir and conjunctival folds (Figure 13) Commonly the reservoir over the nasal and temporal conjuncriva is disturbed by the presence of conjunc- rival folds. 26,27 Conjunctival folds have been linked to subjective symptoms of dryness and can produce tear film instability over the conjunctival surface even in the presence of a normal level of tear secretion. When they are present, they affect the morphology of the reservoir which loses its meniscus shape and follows the contour of the underlying conjunctiva. This is seen with the Tearscope Plus as a widening of the black central band and a reduction of the bordering white bands. This reduced volume witl create a thinner pre-conjunctival tear film, symptoms of conjunctival dryness and will induce over a long period of time an increase in conjunctival hyperaemia

Irregular tear reservoir (Figure 12) The reservoir may be interrupted and this is one of the signs of the potential dry eye symptoms. In this case the irregularity is readily seen with the Tearscope Plus observation even when they relate to lid edge morphological changesY

Figure 11

Figure 10 Figure 12

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JEAN-PIERRE GUILLON

over the whole exposed area. The worse the folds the wider the black band and the most noticeable the symptoms.

The presence of conjunctival folds complicates further some other tests of tear measurements. When Schirmer tests or thread tests are used to measure tear secretion, they are usually placed in the temporal third area of the lid. Those tests rely on the presence of a representative tear reservoir for their moistening. It is evident that the reduced volume present in these conditions wilt further limit the relevance of the tests when performed in the patients presenting conjunctival folds.

Abnormal reservoir behaviour With ageing, the lower lid edge may not conform properly with the ocular surface and moves away from it during the blink sequence. When this is the case, the rese~-voirs do not meet and decreased efficiency of the tear spreading mechanisms occurs limiting tear film thickness and reducing its stability.

Observation of the Blink Sequence and Tear Film Motion The practitioner can observe the blink sequence and its effect on the spreading of the superficial lipid layer. Ideally the lipid pattern should be even over the whole surface and any secretion should disperse within the layer in a few blinks. Observing the debris present at the lipid surface and rating its motion has been advocated as a measure of viscosity of the tear filmY This may be useful when artificial tear formulation are used. Incomplete blinks

When a large proportion of the blinks are incomplete the upper lid does not collect fluid from the inferior reservoir and this limits the volume of fluid used for resurfacing the tear film. The uncovered area also will be the main site of prolonged tear film break, leading to cell necrosis and the pattern of inferior fluorescein staining observed in marginal dry eyes. In cases where blepharifis is present the drainage effect from the inferior meniscus is maximised and the pattern of 'Smile' staining will appear in the vicinity of the lid edge. In both situations there may be a localised decrease corneal sensitivity and a delayed reflex blink response leading to further surface damage.

Infrequent blinks A reduced blink rate will leave the tear surface unprotected for longer periods during which the evaporative effect will take place causing multiple breaks to form and allowing any break in the tear film to increase in size. In normal conditions a blink occurs on average 12 times a min corresponding to an inter-blink phase of around 5 s. It has been shown that these values vary with different visual tasks such as reading and using a VDU during which instability of the tear film and symptoms of dryness will increase.

These observations can be done routinely and the patient can be advised at the first visit or blink training and be made aware that unless progresses are made, the prospects of comfortable lens wear will be severely limited. 29

Measurement of the Non-invasive Break-up Time Following the grading of the undisturbed lipid layer pattern and tear reservoir morphology, the Non-Invasive Break-Up Time (NIBUT) can be measured. The Tearscope Plus has an integrated timer for this purpose. The use of fluorescein has been shown to disturb the tear film) ,~1 With the Tearscope Plus, two techniques of measurement can be used. A direct measure without grid and an indirect measure with the help of a grid insert. NIBUT without grid

This is a direct measure of NIBUT because there is constant observation of the tear film and its break. This also allows the observation in pathological dry eye or blepharitis of the interaction of the lipid layer with the mucous covered ocular surface when it is one of the causes of the break itself. It also allows classification of the type of break seen. When the lipid layer has a poor reflectivity (as in the thin open meshwork or in the presence of a light coloured iris), the observations are more difficult and measurement of the NIBUT can be made with the use of the fine grid insert.

Figure 13 Figure 14

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NON-INVASIVE TEARSCOPE PLUS ROUTINE FOR CONTACT LENS FITTING

With grid (Figure 14) This is an indirect measure of the NIBUT because the tear film itself is not seen but the measurements are made by observation of the regularity of the image of the fine grid produced by the tear film surface acting as a mirror. When the tear film is regular it acts as a perfect mirror and a regular image of the grid seen. When the tear film breaks it acts as a broken mirror and a break or distortion appears in the grid image.

Measurement routine for the clinician The measurement of the break is the time taken between the blink and the appearance of a disconti- nuity in tear film coverage or that of a distortion in the grid pattern. The patient is asked to keep both eyes open during the measurement, ff a blink occurs before a break is seen the timing is noted and recorded as such. It is easy to understand that a reflex blink can occur following a break in the other eye or following a break over the conjunctival surface. Because the eyes are kept open for longer periods than usual (over 25 s for normal tear films), it is better to alternate the eyes when repeated measures are taken as follows: Right eye, Left eye, Left eye, Right eye, Right eye, Left eye. This limits the effect on the fellow eye and allows the recording of the minimum value, maximum, median and calculation of the mean for further comparisons.

Type and location of break

Types: Spots, Streaks, Meniscus induced, Band, Surface Round spots or elongated streaks are most common and seem to be an individual characteristic or induced by the meniscus along the lid. On soft contact lenses breaks also occur as horizontal bands when the aqueous phase thins or as a surface break when it occurs over a whole area.

Location 5: corneal areas, Upper lid, Lower lid As for staining patterns, the cornea is divided into central, nasal, temporal, superior and inferior zones. The upper and lower locations reflect the meniscus- induced break occurrence. More than one location represents multiple breaks or single breaks occurring over a large area.

Testing for Meibomian gland blockage In all cases the effectiveness of meibomian secretion should be checked to rule out any blockage (especially when the reservoir presents any irregularity) and one can detect reduced secretion (when the lipid layer has an open meshwork pattern of low visibility). The lower lid is gently squeezed three times between the thumb and forefinger near the lid edge. In most cases this gentle pressure should be sufficient to expel a small quantity of lipids from the glands. It should be observed as it progresses upwards and mixes with the background lipid layer following each blink. If little or no lipid can be expressed it is unlikely for meibomian secretion to be effective under the sole action of blinking. If globules of lipid are present, they corre- spond to lipids with poor melting properties and treatment with hot compresses and lid squeezing should be advised. If, following a few blinks, the lipid layer has not changed in pattern or only one grade in the thickness range, blockage or reduced secretion is suspected. It has been demonstrated that squeezing of the lids produces an increase in lipid layer thickness and tear film stability over a period of time. It has been shown that meibomian therapy by repeated gland expression and lid massage was useful in problematic lens wear 32 and that the lipid layer thickness was increased in humid environmentsY

Corneal Surface Irregularity When damage of the corneal surface is suspected, as in dry eyes or following contact lens wear, it is important to detect any surface anomalies which need to be exanained or followed up. These include the presence of pingueculae, pterygium, 3 and 9 o'clock corneal irregularities, erosions, localised corneal damage present in blepharitis or tear film induced pathology. In such cases the flexible inserts are used as follows:

Any distortion of the corneal surface will be seen as a distortion of the reflected insert and will be present immediately following the blink and always in the same position regardless of tear film coverage.

Checking for evidence of reflex secretion Following the NIBUT measurement, the practitioner should reassess the lipid layer pattern and the status of the tear reservoir for any evidence of tear reflex induced during the measurement. Lipid layer reflex secretion is seen by an increase in lipid layer thickness and visibility which occurs in the following order: Open Meshwork, Closed Meshwork, Wave, Amorphous, Normal colours, Abnormal colours, Globular. Aqueous reflex secretion will be visible as an increase in tear reservoir height and flattening of its curvature (seen as a darker central black band) or as bulging outwards towards the lid edge. F igure 15

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JEAN-PIERRE GUILLON

Ring insert (Figure 15) This is best used for detecting large distortion such as those present in keratoconus or extensive corneal surface damage following lid closure anomalies, pterygium or long term 3 and 9 o'clock dryness. In the last case corneal epithelial staining may disappear in a matter of days or weeks but the distortion may take as long as 6-9 months before it disappears. Re-fitting is only advised following full recovery from the induced corneal distortion.

Coarse grid insert For medium distortion such as those produced by cell necrosis inferiorly in blepharitis and inferior dryness with contact lens wear or advancing pinguaculae. Again full corneal recovery will be achieved only when the distortion has disappeared. The tear film and the grid reflection are not situated in the same plane. In the routine use of the fine grid, the examiner focuses on the tear film using the white out of focus background, then advances forward to focus on the grid reflection to check for distortion. When distortions are seen, focus- ing back on the tear film will demonstrate if the site of the distortion is also the site of tear film break-up or abnormal coverage.

stability resemble more closely that found in Sj6- gren's syndrome than in the normal pre-ocular tear film. The epithelium damage occurring in Sj6gren's syndrome is replaced by a deterioration of the lens surface qualities and poor surface wettability which results in increased deposition and denaturation of the biofilrn. Luckily this can be counteracted by the judicious choice of lens material or lens wear modality based on the individual observations of the drying pre-lens tear film with the Tearscope Plus.

Structures seen with the Tearscope Plus (Figures 16 and 17) Lipid layer: The uppermost lipid layer is highly

reflective and is seen moving at the surface when present.

Aqueous phase: When the lipid layer is absent or thin, the lens surface is reflective, the mucous coverage is limited or dehydrating, the conditions are ideal for the production of interference fringes within the aqueous phase. All the above conditions are also present in pre-lens tear film of low stability when symptoms are more likely. This is the only way

Principle of Tear Film Instability on Soft Contact Lenses Two surfaces are at the origin of dryness symptoms in soft contact lens wear; the contact lens surface covered by the pre-lens tear film and the corneal surface covered by the post-lens tear film. In the ideal situation, a stable pre-lens tear film will protect the lens surface from deposition and the lens matrix from dehydrating. In the worst case an abnormal pre-lens tear film will induce an accelerated deterioration of the lens surface qualities, producing the dehydration of the post-lens tear film by pervaporation through the lens and induce corneal damageY Observation of the pre-lens tear film and its deterioration with the Tearscope Plus allows differentia- tion between a normal and abnormal PLTF.

Tearscope Plus use during Fitting and Contact Lens After-care Normal fluorescein cannot be used with soft lens wear and most tests offer very little supplementary information on the nature of the tear reservoir, the pre-lens tear film, its thickness, its structure or its spreading. It is during the examination of contact lenses that the Tearscope Plus is most useful and innovative.

Figure 16

Pre-Sofl Lens Tear Film Structures Guillon 16 has shown that the tear film covering any

soft contact lens is reduced in most of its components. The lipid, aqueous and mucous layers are thinner than the patient own pre-ocular tear film. The lens surface also has reduced wetting properties as it does not possess, like the corneal epithelium, an anchorage system for the mucuous layer.

In fact the pre-lens tear film structure, behaviour and Figure 17

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NON-INVASIVE TEARSCOPE PLUS ROUTINE FOR CONTAC~I" LENS F1TFING

to visualise the aqueous phase over a large area and map the thickness variation and distribution during the inter-blink.

Mucuous layer and lens surface When the aqueous phase disappears the mucous layer becomes visible and is seen dehydrating. If a blink does not reform the pre- lens tear film, the lens surface becomes visible.

Routine for Observation of the Pre-Lens Tear Film

Lipid layer presence The first thing to observe is the presence of a lipid layer. When only a thick (Amorphous) lipid layer is seen, it

is a sign of good protection from evaporation and is usually present when a thick underlying structure exists such as a thick aqueous phase and adequate mucous layer. This is the ideal PLTF linked to increased stability with limited deterioration with wear and time. In this case, most contact lens wear modalities can be utilised.

When the lipid layer is absent, increased evaporation from the aqueous phase is most likely. When combined with a thin mucous cover, the fringe system formed within the aqueous phase will be easily seen and drying of the PLTF will occur as bands or over the whole lens surface. In this case a material known for reduced fluid loss can be chosen (such as Proclear or Benz) and ultra thin lenses must be avoided (thicker lenses will limit the effect of pervaporation).

When the lipid layer is seen to break at the surface of the lens, it appears as bright reflective zones over the dry spot (Figure 18). This is the sign of active contamination of the underlying mucous layer where non-wetting patches can occur immediately following the blink. Localised dryness results as well as accelerated deposition. Regular replacement is the modality of choice and is based on the PLTF NIBUT whereby the shorter the NIBUT, the more frequent the replacement. Guillon et a124 have proposed that to avoid complications, replacement should occur when the pre-lens tear film NIBUT is less than 8 s and has decreased by 25% from its baseline measurement, or when it is inferior to 4 s.

When the lipid layer is visible and has normal appearance (Meshwork or Wave) it provides some protection from evaporation and fringes in the underlying aqueous phase will only be seen when the mucous coverage is not maximal. When this appearance is linked to a reduced stability or an irregular and thin tear reservoir, the practitioner can suspect the possible onset of dryness symptoms late in the day and advise the use of re-wetting drops at that time. The next observation is that of the tear reservoir forming over the lens surface.

Tear Reservoir in Soft Lens Wear During contact lens wear the tear reservoir is further disturbed by the presence of the lens whose surface is

Figure 18

less than adequate to provide support for an ideal tear film.

Soft lens materials, unlike the cornea, do not possess an anchorage system for the establishment of a stable mucuous coverage and pre-lens surface wetting relies mainly on the weak electrical attractions occurring at the lens surface and within the water molecules to establish a mucous coverage by spreading during the blink action. This less than ideal surface wetting may induce an increased instability in the area of the tear reservoir soon after its formation resulting commonly in excessive meniscus induced thinning) and corneal staining produced by evaporation through the lens. This staining may be seen near the lid edge and its severity will depend also on the thickness of the lens in this area, the lipid coverage and the ability of the lens material to retain water within its matrix. The greater the thickness of the lens and the lower the loss of water, the less the influence of meniscus induced thinning.

If an irregular, thin or curved reservoir is seen, less fluid is available for PLTF formation and a reduced aqueous thickness is suspected with potential dryness symptoms. On the other hand, if a full reservoir is present front lens wetting will be adequate in the presence of a full blink repeated at suitable regular intervals.

Protection Mechanism in Soft Lens Wear The contact lens protects the cornea by acting as a buffering zone from the effect of its drying surface. The blink reflex is not triggered by a break in the pre-

lens tear film and the delay may be quite significant. During this delay, two processes may take place. A process of deposition and a process of evaporation. Their occurrance and interaction is dependent on the structure of the pre-lens tear film, the duration of the delay and characteristics of the lens material.

Lens surface deposition occurs when superficial lipids come in contact with the mucous coverage and dryness and deposition will be accelerated.

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JEAN-PIERRE GUILLON

Evaporation from the lens surface. When the pre-lens tear film is devoid of superficial lipid layer and the unprotected aqueous phase evaporates it produces a dehydration of the mucous layer revealing the lens.

The lens surface, when devoid of mucous, aqueous and lipid coverage, acts as the ideal site for evaporation drawing fluid from the lens matrix. When driven by external conditions of reduced humidity, dehydration is accelerated, reaching the post-lens tear film and creating epithelial stainingY

Protection during Overnight Wear It has been shown 36 that during overnight wear, dehydration of the mucous layer of the PLTF occurs and effectively protects the contact lens surface. During the process of waking, first the mucous layer is re- hydrated by the influx of aqueous tears producing a very viscous tear film. The lipid secretion that follows stabilises the whole structure. If reduced secretion is suspected, the use of non-viscous eye drops such as unpreserved saline is advised on waking. Early symptoms may be caused by the lids moving over the drying lens surface or felt over the unprotected conjunctival area. Prolonged wear of a lens not protected by a functional pre-lens tear film may cause epithelial damage by pervaporation through the lens.

Conclusion The Tearscope Plus :~7 provides the practitioner with non- invasive information on the structure and behaviour of the tear film over the ocular surface and its interaction with contact lenses. This permits a more effective choice of mode of lens wear with the aim of limiting the symptoms and the effect of dryness.

Address for Correspondence Dr Jean-Pierre Guillon, FCOptom, 35 Heyford Avenue, London SW8 lEA.

REFERENCES

Wolff, E. The muco-cutaneous junction of the lid margin and the distribution of the tear fluid. Trans. Ophthalmol. Soc. UK., 66, 291 - 308 (1946). Tiffany, J.M. Tear f i l l stability and contact lens wear. J. Br. Con. Lens Assoc., 11, 35-38 (1988).

3 Prydall, J. and Campbell, F. Study of tear film thickness and structure by interferometry and confocal microscopy. Invest. Ophthalmol. Vis. Sei., 33, 1996-2005 (1992).

4 Dilly, P.N. Conjunctival cells, subsurface vesMes, and tear f i l l mucus. In: The Preocular Tear Film in Health, Disease, and Contact Lens Wear, Ch.61: 677-687. (Ed) Holly, F. J. (Dry Eye Instit, Lubbock, Texas) (1986).

s Carney, L.G. and Hill, R.M. Variation in blinking behaviour during soft lens wear. Int. Con. Lens Clin., 11,250-253 (1984).

6 Doughtly, M.J., Fonn, D., Richter, D., Simpson, T., Caffery, B. and Gordon, K.A. A patient questionnaire approach to estimating the prevalence of dry eye symptoms in patients presenting to optometric practices across Canada. Optom. Vis. Sci., 74, 624- 631 (1997).

7 Holly, F.J. Formation and rupture of the tear film. Exp. Eye Res., 15, 515-525 (1973).

8 McDonald, J.E. and Brubaker, S. Meniscus induced thinning of tear films. Am. J. Ophthalmol., 72, 139-146 (1971).

9 Fatt, I. Observation of tear film break up on model eyes. CLAO J., 17, 267-281 (1991).

10 Golding, T.R., Bruce, A.S., Mainstone, J.C. Relationship between tear meniscus parameters and tear film breakup. Cornea, 16, 649 - 661 (1997).

11 Craig, J.P., and Tomlinson, A. Importance of the lipid layer in human tear film stability and evaporation. Optom. Vis. Sci., 74, 8- 13 (1997).

12 Gilbard, J.P., Farris, R.L. and Santamaria, J. Osmolarity of tear microvolumes in keratoconjunctivitis sicca. Arch. Ophthalmol., 96, 677-681 (1978).

13 Gilbard, J.P., Graz, K.L. and Rossi, S.R. A proposed mechanism for increased tear film osmolarity in contact lens wearers. Am. J. Ophthalmol., 102, 505-507 (1986).

14 Bianchii, C. (1997). BUT revised in the light of the Tearscope findings. Video session. The American Academy of Ophthalmology San Francisco (Nov 1997).

15 McCulley, J.P. and Sciallis, G.F. Meibomian keratoconjunctivitis. Am. J. Ophthalmol., 84, 788-793 (1977).

16 Guillon, J-P. (1990). Tear film structure of the contact lens wearer. PhD Thesis. The City University, London.

17 Nakamori, K., Odawara, M., Nakajima, T., Mizutani, T. and Tsubota, K. Blinking is controlled primarily by ocular surface conditions. Am. J. Ophthalmol., 124, 24-30 (1997).

18 TEARSCOPE PLUS CLINICAL HAND BOOK AND TEARSCOPE PLUS INSTRUCTIONS. (1997). Keeler Ltd. Windsor, Berkshire. S14 4AA., Keeler Inc, Broomall (PA) USA.

19 Guillon, J-P. and Guillon, M. The role of tears in contact lens performance and its measurement. Contact Lens Practice (Ed) M. Guillon and M. Ruben (Chapman and Hall, London): 453-484 (1994).

2o Fogt, N., King-Smith, E.P. and Tuell, G. Intefferometric measurements of tear f i l l thickness using spectral oscillations. J. Opt. Soc. Am. (in press) (1997).

21 Syffoc. (1995). Enqu~te SOFRES Oct 1994. Communiqu~ de presse du 27-01-95.

22 Guillon, J-P., Guillon, M. and Malgouyres, S. Desiccation staining with hydrogel lenses: tear film and contact lens factors. Ophthal. Physiol. Opt., 10, 343-350 (1990).

23 Fontaine, A. Influence des cosmetiques sur la contamination du film lacrimal et des panpi~res. Memoire de maitrise de sciences et technique d'optique. Universite de Paris Sud (XI) Centre scienti- fique d'OrsayAline & Guillon, J-P. (1997).

24 Guillon, J-P. and Guillon, M. Tear film examination of the contact lens patient. Contax, May 14-18 (1988a).

25 Hykin, P.G. and Brnn, AJ. Age related morphological changes in lid margin and Meibomian gland anatomy. Cornea, 11, 334-342 (1992).

26 Rolando, M. and Macri, A. Low tech detection of tear f i l l related eye surface pathology. In Murube J. Ojo Seco - Dry Eye Soc. Espan. Oftalmol. Marid. Technimedia Editorial. (1997).

27 Hoh, H., Schirra, F., Kienecker, C. and Ruprecht, kW. Lid-Parallel Conjunctival Fold (LIPCOF) and dry eye: A diagnostic tool for the contactologist. Contactologia, 17, 104-117 (1995).

2s Schuller, W., Young, W. and Hill, R.M. Clinical measurements of the tears: viscosity. Am. J. Optom. Physiol. Opt., 43, 1358-1361 (1972).

29 Hi l l , R.M. and Carney, L.G. The effect of hard lens wear on blinking behaviour. Int. Con. Lens CUn., 11,242-248 (1984).

3o Mengher, L.S., Bron, AJ., Tonge, S.R. And Gilbert, D.J. Effect of fluorescein instillation on the pre-corneai tear film stability. Curr. Eye Res., 4, 9-11 (1985b).

al Pate1, S., Murray, D., McKenzie, A., Shearer, D.S. and McGrath, B.D. Effect of fluorescein on tear break up time and on tear thinning time. Am. J. Optom. & Physiol. Opt., 62, 188-190 (1985).

3") Pangh, J.R., Knapp, L., Martinson, J.R. and Homm, M. Meibomian therapy in problematic contact lens wear. Optom. Vis. Sci., 67, 803 -806 (1990).

33 Korb, D., Greiner, J.V., Glonek, T., Esbah, R., Finnemore, V.M. and Whalen, A.C. Effect of periocular humidity on the tear film layer. Cornea, 15, 129-134 (1996).

34 Guillon, M., Allary, J.C., Guillon, J.P. and Osborne, G. Clinical management of regular replacement: Part 1. Selection of replacement frequency. Int. Contact Lens Clin., 19, 104-120 (1992).

35 LiNe, S.A. and Bruce, A.S. Role of the post lens tear film in the mechanism of inferior arcuate staining with ultrathin hydrogel lenses. CLAOJ., 21,175-181 (1995).

36 Guillon, M. and Guillon, J-P. Hydrogel lens wettability during overnight wear. Ophthal. Physiol. Opt., 9, 355-359 (1989).

3~ Guillon, J-P. The Keeler Tearscope Plus. An improved device for assessing the tear film. Optician, 213, (5594), 66-72 (1997).

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Non-invasive tearscope plus routine for contact lens fitting