Ординатура / Офтальмология / Учебные материалы / Orthokeratology Principles and Practice 2004

244 ORTHOKERATOlOGY

Table 9.4 An example of the daily disposable lens powers that might be issuedto a -2.50 0 myope in the first week of night therapy using single reverse geometry orthokeratology lenses

Table 9.5 lists typical normal and abnormal symptoms that may arise in both overnight and

daytime orthokeratology. Recognition of abnormal symptoms is vital if complications are to be avoided. Familiarity with the typical range of mild symptoms and signs arising during orthokeratology treatment is essential to enable the practitioner to manage patients conscientiously.

Quality of vision should be assessed both with and without the lenses in situ. In the case of overnight orthokeratology, the quality of vision with the lenses in place is almost irrelevant, but clearly needs to be adequate for patients to find their way about indoors and function normally if they awaken during the night. Obviously, the quality of this aspect of vision is more important for the daytime wearer. Of more interest is the quality of vision on lens removal. This will be both an assessment immediately on lens removal

Dry sensation towards the end of the wearing period which resolves on removal of lens

Slightsore or puffy feeling to the eyelids improved by removing lens

Slightincrease in the amount of "sleep" found at the inner canthus on awakening (nighttherapy)

Occasional misting of the vision during the day improved by removing lens and cleaning it or several forced blinks (daytime wear)

Imperfect vision through existing spectacles following lens removal (all modalities) or

slightlyimperfect vision with dailydisposable lenses worn during day (nighttherapy)

Marked drysensation or dryness not resolved by removing the lens

Obviously red or swollen eyelids or soreness or puffiness not resolved by removing the lens

Discharge collecting on the eyelids and lashes on awakening (night therapy)

Vision mists over shortlyafter insertion or misting at anytime not resolved by removing and cleaning lens (daytime wear)

Anydistortion apparent when examining text at near point without lenses in situ (all modalities)

Lenses immobile onawakening but start to move after a few minutes or after instillationof onedrop artificial tears and indenting sclera (night therapy)

Immobile lens not freed by use of scleral indentation and artificial tear instillation or producing pain on removal (night therapy)

and then of the stability of this vision during the day.

Where daily disposables are being worn, patients should be questioned as to the powers in current use and the quality of the vision through them.

VISION WITH LENSES IN SITU

Where lenses are going to be worn during daytime hours, it is most important to ascertain the quality of the visual result and overrefraction in the normal manner. Thus any deficiencies can be corrected to optimize the corrected acuity. The major difference between orthokeratology and conventional RGP lens fitting when considering this subject is the presence of a negative-powered liquid lens between the lens and the cornea. In a conventional alignment RGP fitting, the liquid lens serves to correct solely the front-surface corneal astigmatism. In the case of orthokeratology this is still true, but in addition the tear lens may correct up to 4 0 of myopia. This arises because the lenses are fitted flatter than the underlying central cornea. The general clinical rule of thumb applied in these circumstances is that for every 0.1 mm that the lens is flatter than the underlying cornea, there is a tear lens with a power of -0.50 O. This optical effect is predicted by the difference in refractive index between the lens material (typically about 1.47) and the tear film (taken to be 1.336). Thus, depending on how flat the central fitting is, the lens back vertex power will have been reduced accordingly.

Where the patient is wearing the lenses overnight, there is little point in performing an overrefraction since the lens will generally be worn with the eyes closed and a plano lens offers the best equivalent oxygen percentage (EOP) profile. Another advantage of ordering a plano lens is that it can be retained as a future trial lens should a second lens be necessary.

Given that the patients will typically be myopes between -1.00 and -4.00 0, then the negative liquid lens will usually be sufficient to correct the majority of the ametropia, allowing good functional vision. If plano lenses are used, this minimizes lens thicknesses and improves oxygen transmissibility. In normal circumstances

in night therapy practice it is rarely necessary to check the vision and overrefraction with the lenses in place.

LENS MOVEMENT AND POSITION

The next examination that takes place following the symptom and acuity recording is the examination of lens movement using white diffuse light (to reduce reflex lacrimation and afford a better view) and low magnification on the slitlamp microscope. If the lens has been worn overnight and the patient is seen more than an hour after rising, following instillation of artificial tears on rising, then there will generally be some lens movement. If the lens is bound and a corneal imprint is visible once the lens is manually freed up, then this may be regarded as an unacceptable degree of lens binding, or at least one that requires careful monitoring. Whether or not binding is evident at this visit, all patients must be shown how to look for lens movement and free up the lens by indenting the sclera and using artificial tears. This is described above under wearing schedules.

No lens binding should occur during a daytime trial and, if it does, this must be regarded as an adverse sign. Should this arise, then the practitioner is advised to follow the problemsolving approach set out later in this chapter.

Given that a very typical diameter for an orthokeratology lens is between 10.00 and 11 mm, the amount of movement seen on blink is relatively small. It is of the order of 1.00-1.50 mm. This can be seen at the same time as one is looking for binding. It is relatively easy to judge lens movement amplitude at low magnification, if it is compared to anatomical features such as the pupil border to inferior limbus distance. If the pupil size is 4 mm and the horizontal visible iris diameter is 12 mm, then this distance will be 4 mm, so that a movement of 1 mm will be equal to approximately a quarter of the pupil border to inferior limbus distance.

The direction of movement should always be vertical and an arcuate movement will almost always indicate a lens that is too flat or an eye that has significant against-the-rule astigmatism. The use of the push-up test, where the lids are

246 ORTHOKERATOLOGY

Figure 9.10 Simple means of recording 1.5mm of inferior temporal decentration of a right lens. The ends of the lines represent the edges of the cornea and the dot the lens center.

separated and the lens is pushed upwards with the lower lid and allowed to fall, is useful for establishing that there is no arcuate movement.

Another observation to be made at this stage is the habitual riding position of the lens. To assess this the patient must have the eye in the primary position, so it may be appropriate to use a fixation target. Centration is typically recorded as the amplitude of decentration from the pupil center in millimeters, together with the direction. For example: 1.5 mm inferotemporal de centration. The use of a simple cross to represent the cornea together with a spot to represent the lens center is a useful means of representing decentration. For example, 1.5 mm inferotemporal decentration in the right eye would be recorded as shown in Figure 9.10.

For daytime wear, this measure of centration is sufficient. The topographic change map usually confirms that the lens is decentered in the manner recorded, in that the zone of flattening is decentered in a similar manner. However, for overnight wear the situation is more complex. The authors

have observed several cases where the centration of the lens at first follow-up was less than ideal, but when the lens is centered on the cornea, the fit was perfect. However, when the topography difference maps were inspected the treatment zones were perfectly centered. This implies that the centration exhibited by a lens in daytime wear can be quite different from that in overnight wear. Presumably this is due to a variation in gravitational forces when lying down, together with the absence of blinking, and the different relationship of the lids to the lens.

Therefore in those patients on night therapy, more attention should be paid to the position of the zone of flattening measured using videokeratoscopy than the apparent lens centration with the eyes open. Figure 9.11 shows a topographical change map for a patient who had a narrow palpebral aperture and on whom trial lenses always rode low when seated in the consultingroom chair. However, the results in terms of the centration of the flattened zone on the cornea indicate that the lens must center correctly with the eyes closed. The fluorescein pattern with the lens manually centered also demonstrated all the correct attributes of an orthokeratology fitting.

FLUORESCEIN FIT ASSESSMENT

It is probably true to say that, providing the topographic response of the cornea is correct and the

Figure 9.11 Topographical changes in a patient wearing a lens that was consistently decentered in primary gaze with the eyes open, yet produced a perfectly centered zone of flattening.The lens must ride in the correct position during sleep.

cornea shows no adverse response to contact lens wear, then the fluorescein assessment of lens fitting is almost irrelevant. However, the vast majority of practitioners will want to look at the lens in situ at least once, if for no other reason than to ensure that it is not binding. Thus, as already stated, at this first aftercare visit the night therapy patient will generally attend wearing the lenses, allowing this determination to be made. Having the patient attend the practice on at least one occasion wearing the lenses has the further advantage that the cornea can be assessed immediately on lens removal, allowing any staining and edema to be seen that might otherwise have resolved by the time the patient gets to the practice after awakening.

Fluorescein instillation should be left until the movement, centration, and surface wetting of the lens have been assessed in case the extra fluid causes a change in these features. The postwear fluorescein pattern should not differ significantly from that observed on first insertion. The apparent depth of the tear reservoir may be slightly reduced but otherwise the features of the fluorescein pattern are as shown in Chapter 6.

Where this is not the case and the topographic change difference map shows anything other than a bull's-eye response, then the practitioner must resolve the deficiencies of the fit and, if necessary, schedule a retrial with an appropriately modified trial lens or ordered lens.

It is generally easier to inspect the fluorescein fitting at the slit lamp. This has several advantages over the hand-held Burton lamp. Firstly, the patient is already seated at the instrument and all one need do is instill fluorescein and inspect the fitting. Secondly, the use of a barrier filter to enhance the fluorescence is much easier at the slit lamp. Thirdly, the higher magnification afforded by the microscope permits the practitioner to observe more of the subtle indicators of an imperfect fitting, for example, persistent bubbles within the tear reservoir, bubbles at the lens edge, inadequate differentiation between tear reservoir and peripheral bearing zone, no tear flow through the fenestrations. Fourthly, several modern RGP lens materials incorporate an ultraviolet filter that prevents fluorescein from being properly activated. Clearly, nobody should be practicing orthokera-

tology without a slit lamp, so the use of a separate lamp to inspect the lens fitting is probably unnecessary.

A small quantity of dye is instilled directly from a fluoret (fluorescein-impregnated strip). The strip is wetted firstly with only one drop of sterile saline. Flooding the eye with fluorescein will lead to greater difficulty in analysis of the fit by virtue of front surface fluorescein and the extra tear volume will give a false impression as to the essential balance between the zones of "contact" and clearance. In addition, a large quantity of fluorescein simply does not fluoresce very much. It is more difficult to instill the correct amount of dye from a minim or other form of ready-mixed fluorescein.

Whatever the riding position, the fluorescein pattern should be assessed with the lens held in the centered position with the lids and the fingers. It is impossible to determine the reasons for lens decentration with the lens decentered, since the lens will be resting over peripheral cornea and an asymmetric pattern will result.

As described in Chapter 6, there is now a variety of genuinely different lens designs on the market. However, when correctly fitted, the fluorescein patterns are very similar.

During the assessment of the fluorescein pattern, the practitioner will be able to inspect the fenestrations (if present) for any sign of tear flow through them. During normal blinking, it should be possible to observe the outward flow of fluores- cein-laden tears through the fenestrations. This is another sign that lens movement is occurring and that the lens is not bound. It is believed that the fenestrations help reduce the lens to unbind on awakening, after instillation of artificial tears.

POSTREMOVAL VISUAL ASSESSMENT

On removal the unaided vision should be recorded. This is a crucial indication of the efficacy of the procedure in meeting patients' expectations. Depending on the lens type and degree of initial myopia, this change may be marked or relatively minor. One of the rewarding aspects of orthokeratology practice is seeing the satisfaction of patients experiencing improved vision on the removal of their lenses.

Additionally, the refraction on lens removal should be measured together with the corrected acuity. It is not acceptable for there to be any reduction of best-corrected visual acuity. The patient and practitioner may have to accept a little induced against-the-rule astigmatism, particularly in the early stages, as described in Chapter 7, but neither this nor any induced mild peripheral corneal distortion should lead to loss of full visual potential with refraction. If it does, then careful attention to the fit should be made and if necessary the patient discontinued from the procedure.

Corneal examination

At any aftercare visit there should be no significant increase in limbal or bulbar hyperemia, providing a very high-Dk material has been used. This is in marked contrast to conventional extended-wear hydrogel lens wear where an increase in limbal hyperemia after overnight wear is almost universal (Holden et al1986). Hyperemia is best assessed using diffuse illumination at low magnification. Then using direct focal illumination, the cornea is examined for any sign of edema.

If corneal striae or even folds are seen in a patient wearing a high-permeability lens for overnight wear or, even more unlikely, in a daytime-wear patient, then it is evident that the degree of metabolic embarrassment is too much for the cornea concerned. It may be that moving patients to daytime wear would enable sufficient oxygen to pass to the cornea, but if not, it is best to advise patients that orthokeratology is not a viable procedure for them and it should be discontinued.

Corneal microcysts will not be observed after one wearing session as these are a longer-term response to hypoxia. However they have not been observed to date by the authors in any patient at any aftercare visit. Central corneal clouding, as seen in polymethyl methacrylate (PMMA) wearers, should never be seen in overnight orthokeratology patients, as the degree of corneal edema produced is extremely low (see Ch. 3).

If the technique of overnight orthokeratology brings any surprise to the experienced contact

lens practitioner, it is the near-total absence of corneal stain following a successful overnight wear. One hour or so after rising, when the patient attends at the practice, there should be no more than grade 1 or 2 (trace or mild on the Cornea and Contact Lens Research Unit (CCLRU) scale) central stain, no 3 and 9 0' clock stain, and only the faintest indication that the lens bound during the night. Figure 9.12 shows the features of a just acceptable corneal response in terms of stain. There is grade 2 nonconfluent stain, which would require careful monitoring by the practitioner. The causes and solutions for corneal staining are dealt with later in the problem-solving section. To improve the visualization of fluorescein stain, the practitioner is recommended to use a Wratten 16 yellow filter, as was used to view the fitting pattern.

Typical adverse responses are evident as grosser degrees of stain, particularly if confluent. Figure 9.13 shows significant confluent stain. Figure 9.14 shows a gross degree of compression stain associated with severe binding, which occurred during a daytime trial. This will usually be associated with limbal desiccation stain, in the approximately "3 and 9" format. When severe binding occurs overnight, there is no limbal stain of this sort since no desiccation occurs. However, if the lens binds off-center, there may be some compression of the bulbar conjunctiva.

Equally, in daytime wearers, there should be only minimal corneal response, although there

Figure 9.12 Grade 2 nonconfluent stain in a patient immediately following removal of the lens at the first aftercare.

Figure 9.13 Unacceptable confluentgrade 3 stain following overnight lens wear (Cornea and Contact Lens Research unit).

Figure 9.14 Unacceptable degree of corneal compression in a daytime wearer. Note that there isalso stain over the limbus representing desiccation of the cornea.

may be a little more lid hyperemia due to the greater lid interaction than occurs compared to overnight wear. Unlike an overnight trial, there should be no sign of any corneal compression due to binding, as the lens should remain freely moving at all times.

A common observation following a short period of lens wear is a degree of corneal "dimpling." This occurs because of bubble formation under the lens, typically under the tear reservoir.

Figure 9.15 Corneal "dimpling" seen on removal of a lens fitted too steeply with a deep tear reservoir.

Figure 9.16 Bubble formation occurring under the edge of an excessively flat lens.

Whilst this can be a sign of a steep fit, if the topographic change map indicated that this is not the case, then the situation should be monitored. Clinical experience indicates that this reduces over time. An example of this dimpling is shown in Figure 9.15. A variant of this arises when bubbles form under the lens edge. This is illustrated in Figure 9.16 and usually occurs when the fit is too flat or the edge clearance is excessive. Discussion of a problem-solving strategy for dimpling is given later in this chapter.

250 ORTHOKERATOLOGY

Corneal topography changes

Currently, there is no better way of evaluating the technique of orthokeratology than by measuring the shape change in the very tissue that is being altered, i.e., the cornea. Whilst, strictly speaking, all Placido disk-based topographers measure the shape of the tear film, it seems reasonable to suppose that, away from the lids, this will be almost the same as the anterior corneal surface.

The attributes of the ideal instrument for the orthokeratology practitioner have already been discussed in Chapter 2, but careful attention to image capture, editing, and analysis will greatly aid in the correct discrimination of the ideal from the imperfect fit. The objective unbiased nature of topography measurement is a marvellous way to validate the technique of orthokeratology and a calibrated instrument of the appropriate quality should be regarded as part .of the essential armoury of the competent orthokeratologist.

It is a well-known fact that the line of Sight and the geometrical center of the cornea do not coincide. Typically, the line of sight is decentered nasally with respect to the center of the cornea. Thus a degree of nasal decentration is by no means a bad thing: the center of the zone of flattening is more likely to be located over the line of sight, which coincides with the center of the eye's entrance pupil (the image of the pupil produced by the cornea). In topographic systems that allow the entrance pupil to be identified (see Ch. 2), it is easy to establish that this has occurred. Where the entrance pupil is not identified, then it is reasonable to assume that the center will typically lie 0.5 mm nasally from the center of the topography map.

As has already been stated, the topography difference map will indicate whether the lens has centered correctly. If there is a continuous ring of mid-peripheral steepening around a zone of flattening which is centered over the middle of the pupil, then a perfect result has been obtained. This aspect of confirming the quality of lens centration is an important one and is not easily done by any other means than sequential topography. In terms of difficulty, the most significant problem that arises in orthokeratology is to ensure that the lens is well-centered.

The analysis of the postwear topography difference map is the same as that set out in Chapter 6, namely the differentiation of the bull's-eye response from central islands and smiley facetype responses.

Clearly, the smaller the treatment zone (see Ch. 7), the more critical is good centration to avoid flare. At aftercare visits, it is crucial that the quality of lens centration, as determined by the topography change map, is thoroughly appraised. At this first visit, it is unlikely that patients will report flare, as the degree of refractive change will generally be modest. However, the practitioner who does not attend to improvement of centration at this visit risks significant problems with poor-quality vision and corneal distortion later.

As has already been described in Chapter 2, the topography plays a vital role in the selection of the first lens by virtue of its ability to measure the apical radius and the eccentricity of the cornea. Clearly,as the cornea changes, so will these values. However, there is no evidence that they are of any value when it comes to refitting the patient with future lenses. This is because of the nature of the topographical change in the cornea. As has already been described in Chapter 7, it has been known for many years that the endpoint of orthokeratology treatment is a spherical cornea.

The posttreatment apical radius and eccentricity data only serve to indicate that the apex of the cornea has flattened and that its eccentricity has changed. The practitioner must carefully inspect the posttrial tangential map to infer what the nature of the topography change is. The endpoint of orthokeratology becomes evident when there is no further refractive change and the central 4-5 mm of the tangential plot is spherical. In addition, the absence of any of the topographical signs of steep or flat fits and the presence of the ideal topographic change indicate that the lens fitting is still optimal. If it is not, then the diligent practitioner will refit until both the fluorescein pattern and the topographical change maps are perfect.

Lens condition

It is unlikely that the lenses will have been damaged by the time of the first aftercare

appointment. However, the practitioner is dutybound to inspect both lenses for scratches, deposits, and blocked fenestrations. This is best done by a combination of two techniques. Firstly, the lens surface is inspected on the slit lamp at medium magnification and using diffuse illumination. Rapid hazing of the surface after blinking may indicate a wetting problem that may be related to poor manufacture or possibly lack of attention to cleaning by the patient. The lenses should be removed, cleaned, and then carefully dried. The clean, dry lens should then be critically inspected either using a loupe or the slit lamp.

A lens is shown in Figure 9.17 that has developed a heavy layer of adherent surface plaque. Figure 9.18 shows a lens that has marked lipid deposition on its surface.

In view of the close proximity of the lens to the corneal surface, any scratches or adherent deposits may give rise to corneal trauma. If the deposits cannot be removed either by using protein remover tablets or by careful cleaning of the lens rear surface using a cotton bud dipped in a contact lens cleaner containing polymeric beads (Boston cleaner), then the lens should be replaced.

Most unlikely at this stage is finding the fenestrations blocked by deposits and other dried ocular secretions. However, this should always be looked for, particularly in a patient who complains of discomfort who was previously a com-

Figure 9.18 Lipoidal deposits on the lens front surface. Courtesy of Pat Caroline.

fortable wearer. The material can be removed by the practitioner by careful use of a cocktail stick and polymeric bead cleaner. Afterwards, the fenestration should be inspected on the slit lamp to ensure that all the material has been removed and that the lens has not been damaged.

Figure 9.19 shows a reverse geometry lens with a blocked fenestration. The debris in the fenestration caused a mild degree of corneal insult which disappeared once it was removed by careful use of a cocktail stick and contact lens cleaner.

Figure 9.17 Example of a scratched lens with associated protein deposition. Courtesy of Pat Caroline.

Figure 9.19 A reverse geometry lens with a blocked fenestration. The debris caused a minordegree of corneal insult.

252 ORTHOKERATOLOGY

DECISION ON CONTINUING SUITABILITY FOR ORTHOKERATOLOGY TREATMENT

By the end of the first aftercare visit, practitioners will be able to decide if the patient has demonstrated the following:

1.satisfaction with the treatment to date and its effectiveness

2.the appropriate improvement in unaided vision

3.no undesirable response in terms of corneal stain, edema, or distortion

4.the appropriate topographical response.

If this is the case then the patient should continue with lens wear and follow the aftercare schedule set out in Table 9.2. If not then the practitioner must adopt a problem-solving strategy and either modify the fit or discontinue the patient from the treatment plan.

VISUAL CORRECTION DURING THE FIRST WEEK

During the first week, patients on night therapy need to be given some form of daytime vision correction. Their existing spectacles are generally now too strong for comfortable use. This is not the case with myopic children who may have an older pair of spectacles that incorporate a lower correction. Those patients with no suitable spectacles (or those who refuse to wear spectacles) need a vision correction to function normally during the day. The introduction of daily disposable soft lenses has made dealing with the progressively reducing myopia much more straightforward. The problems here are:

•The patient has to learn how to handle what is generally a more challenging type of lens.

•The power required will vary during the day and from day to day.

•The existing daily disposable lenses do not correct astigmatism.

•Patients may like disposable lenses so much they decide against orthokeratology - this happens occasionally!

There is little doubt that patients unused to soft lenses can find daily disposable lenses more

difficult to handle initially. The larger diameter, thin substance, and often low modulus of elasticity make them more difficult to insert than an RGP lens. However, with careful instruction it is not a problem. There will be some patients, typically low myopes, who will prefer to do without lenses and tolerate the blur arising from undercorrection of their myopia for the first few days. Others will ask if they can just put in the orthokeratology lenses when they want to see particularly well. This is perfectly acceptable providing the lens has been appropriately powered for their degree of ametropia. But for the vast majority the use of daily disposable soft lenses does not trouble them. It is interesting that several remark how much more comfortable their orthokeratology lenses are than soft lenses. Removal rarely presents a problem.

As described in Chapter 7, the typical dioptric change after the first wearing session with single reverse geometry orthokeratology lenses is approximately 0.75-1.00 O. The practitioner will know from the response trial exactly what change the patient exhibited. Therefore the choice of power for the morning of the first day is relatively straightforward. However, a few hours later regression will have set in and this power will be incorrect. Therefore it is normal practice to give patients a further pair of lenses approximately 0.75 0 stronger to use when they notice the distance vision tapering off. Mountford's study using single reverse geometry lenses (Mountford 1998) shows that in the first week of treatment an average of 1.930 of reduction in apical corneal power (and, by inference, myopia) occurred. This was measured in the morning. Eight hours later, 0.52 0 of the apical corneal power had returned. These are average figures, concealing some diversity in individual patient responses. Notwithstanding this, it does give the orthokeratologist some basis for deciding what powers of daily disposable lenses to issue to the patient. Patients seem to enjoy checking their vision at various times during the day and selecting another lens from their selection as appropriate. It is possible to supply patients with a vision chart so that they can assure themselves that their vision is good enough for driving purposes for the country in which they are resident.

To clarify this area, Table 9.4 shows the powers that might be issued during the first week to a patient with 2.50 D of myopia. Several extra lenses of each power are also issued so that patients can "jump up" (or down) the scale if they feel that their progress is falling behind or exceeding that predicted for them.

The approach described above may seem somewhat crude and unscientific. However, in practice it works perfectly well, providing patients understand the difficulty in giving them a completely accurate lens for both eyes for every minute of the day.

When double reverse geometry lenses are being used, the refractive changes will be much more rapid. Clinical experience indicates that approximately 75% of the final refractive change occurs during the first night of lens wear if the lens fit is perfect. Thus the first overnight trial will indicate the appropriate strength of daily disposable lenses to use on the first day. This may be up to 2.50-3.00 D less than the original refraction, assuming a large refractive change was programmed into the lens design. Subsequent changes will be rapid, meaning that it is unlikely that daily disposable lenses will be required after the first few days. Therefore the practitioner may supply an initial lens power based on the overnight trial and a couple of other lens powers between 0.50 and 1.00 D less than this for the second and third days.

The correction of astigmatism in the first week is more problematic. Assuming that patients have been selected for night therapy on the basis that they have no more than 1.50 DC of with-the-rule astigmatism the uncorrected astigmatism does not generally prove to be a problem. As already outlined in Chapter 7 there is a great shortage of good studies in the time course of astigmatic changes in orthokeratology. What can generally be stated is that the reduction in with-the-rule astigmatism lags behind the reduction in myopia and that a 50% reduction in astigmatism up to -1.75 DC occurs (Mountford & Pesudovs 2002). Patients with astigmatism should therefore be advised that the vision through the daily disposable lens will not be perfect in the initial stages.

FURTHER AFTERCARE VISITS

In terms of the scheduling of further visits, the program set out in Table 9.2 is generally appropriate. However, where the practitioner has made an alteration to the lens fit or wishes to keep a close check on an individual patient, then clearly more frequent visits will be scheduled. Once a patient has reached a stable situation and been followed for 6 months with no problems, then routine follow up is advised every 6 months, as set out in Table 9.2.

Orthokeratology treatment should always be tailored to an individual patient and care taken that the ideal topographic and physiological response is maintained. Practitioners new to the procedure are advised to see the treatment intervals set out in Table 9.2 as minima and always err on the side of caution and see a patient more frequently when they feel that this is clinically indicated.

EMERGENCIES

Increasingly, eye-care practitioners work in a more regulated and litigious environment. It is becoming incumbent on contact lens fitters to provide continuing care, not only in normal consulting hours, but also outside them. It is no longer considered satisfactory to say to the patient: "If you have serious problems outside of working hours, then go to the hospital emergency department." The first piece of advice that should be given is: "if in doubt, take them out." The vast majority of contact lens-induced disorders start to improve on removal of the lens. The practitioner should supply a list of what sort of symptoms may be considered normal during the initial few days of wear, and those that are abnormal and should lead to lens removal and the patient seeking advice from the practitioner. A suggested list of such symptoms is given in Table 9.5, together with indications as to how these symptoms may relate to the mode of wear.

In those instances where simple removal of the lenses does not lead to a reduction and then resolution of the symptom, patients need to know how they should contact the practitioner for