Current Practice

No clinical trials have been conducted to determine the optimal schedule of aftercare visits for contact lens wear. A useful starting point for developing a protocol for contact lens aftercare visits is to consider the actual aftercare visit frequency of contact lens wearers. A survey of 222 current and 258 previous contact lens wearers in the United Kingdom found an average self-reported aftercare visit frequency of once every 1.07 years ( ). As can be seen from Fig. 37.1 , a majority of lens wearers (44%) presented annually for a routine aftercare visit, but a significant minority presented every 6 months (33%) or even every 2 years ( ).

Proportion of lens wearers presenting for aftercare visits at various frequencies.

After Ewbank, A. (2013). Understanding the CL consumer: Part 1 – Buying habits and customer loyalty. Optician , 245 (6400), 38–41.

Recommended Visit Schedules

reviewed the concept of contact lens aftercare and sought to determine the preferred frequency that lens wearers should return for routine visits. Four key clinical reasons for conducting a routine aftercare visit are identified as preserving ocular health, maintaining good vision, optimizing comfort and ensuring satisfactory lens fitting performance. Commercial reasons for conducting aftercare visits were also considered. adopted a 1-year interval as a referent, given that this seemed to be the ‘default’ frequency most adopted by lens wearers.

Based upon these wide-ranging considerations, considered which combinations of lens wear and refractive considerations would indicate longer or shorter intervals between visits, compared with the 12-month referent. The outcome of this theoretical analysis was an aftercare frequency decision matrix to help practitioners decide upon the appropriate time intervals between routine aftercare visits ( Table 37.1 ).

There are two mutually exclusive domains in this decision matrix, which are based on: (a) lens replacement frequency, wearing modality (daily or extended wear) and type (soft or rigid); and (b) the predicted rate of a refractive change. If a lens wearer meets criteria in both domains that suggest different aftercare frequencies, the higher frequency should be adopted.

The first aftercare visit should always take place within 1 week of lens dispensing. This will provide an opportunity to ensure that lenses are being handled and worn in accordance with instructions; to verify that lens performance, vision and comfort are as expected; and to examine the eye for any unexpected early clinical signs or adverse ocular reactions to the lenses or solutions. Current practice is often to only supply enough lenses for the initial wearing period of lens replacement, so as to provide the lens wearer with additional incentive to return for a check-up after 1 week and to obtain an ongoing supply of lenses. During this 1-week aftercare visit, the lens wearer must be advised of the ongoing frequency for routine aftercare visits, as per the decision matrix.

After the 1 week visit, the following time intervals between routine aftercare visits are advised as a general guideline: soft daily disposable, 24 months; soft daily reusable, 12 months; soft extended wear, 6 months; rigid daily reusable, 12 months; and rigidly extended wear, 6 months. These aftercare visit frequencies may need to be adjusted when rapid rates of refractive change are anticipated, such as every 6 months in youth myopia and every 12 months during presbyopia.

Australian and British lawmakers essentially allow optometrists to set the period of validity of a contact lens prescription ( ). Practitioners may therefore choose to align this period of prescription validity with the advised frequency of aftercare visits. Such a strategy would serve the interests of contact lens wearers by (1) providing a safety net to reduce the risk of problems and complications associated with protracted unsupervised lens wear and (2) creating an incentive to return to the practice for an aftercare visit and resupply of lenses.

Caveats

stressed that the aftercare frequency decision matrix must be considered only as a set of general guidelines or as a ‘starting point’ for determining the appropriate aftercare frequency for an individual patient. In this regard, it is necessary to consider numerous caveats that require deviation from the recommended aftercare visit frequencies summarized in Table 37.1 . The following is by no means a complete list but serves to illustrate the flexible approach required in making such determinations:

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  Orthokeratology involves the wearing of rigid lenses overnight ( ) to physically reshape the cornea so as to provide corrected vision while the therapy continues. Frequent modifications in lens design may be required, and the physical and physiological integrity of the cornea needs to be closely monitored. Accordingly, frequent aftercare visits are required at various phases of the treatment, whether it is used to correct stable myopia or to arrest the progression of myopia (‘myopia control’ or ‘myopia management’).

  
  
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  Myopic patients fitted with lenses designed for myopia control may need to be examined more frequently to monitor the efficacy of the treatment ( ).

  
  
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  Paediatric lens fitting may require more frequent aftercare visits as refraction is changing more rapidly and young children are likely to be fitted with contact lenses due to greater refractive or clinical need ( ). Some studies have indicated that children have a greater propensity for adverse events ( ) although others have found low rates of contact lens-associated ocular complications in children ( ).

  
  
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  Therapeutic applications such as paediatric aphakia require frequent aftercare visits given the complexity of fitting contact lenses to infants and the fact that there is rapid growth of the eye during the first 18 months of life. recommend aftercare visits every 4–6 weeks once contact lenses have been fitted successfully. If the infant is wearing the contact lenses on an extended wear basis, a more frequent review may be required.

  
  
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  High ametropia may require frequent aftercare visits, especially if refraction is changing rapidly. High ametropia (>5.00 D) also carries an increased risk of 1.5× for any adverse event and 1.9× for other infectious events compared with low ametropia ( ). As well, high myopia carries a higher risk of associated ocular complications, such as posterior subcapsular, cortical and nuclear cataracts; glaucoma; chorioretinal abnormalities such as retinal detachment, chorioretinal atrophy and lacquer cracks; and tilted, rotated and larger discs as well as other optic disc abnormalities ( ).

  
  
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  Lens wearers with corneal pathology such as keratoconus, corneal dystrophy or postkeratoplasty generally require more frequent aftercare visits as part of their management compared with uncomplicated cosmetic lens wearers. emphasize the importance of monitoring for disease progression in patients with keratoconus – in particular children, who tend to undergo more rapid changes – so as to facilitate appropriate modification to contact lens fitting.

  
  
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  Lens wearers fitted for postrefractive surgery may need to be seen more frequently during the first 12 months following surgery, as corneal sensitivity may be reduced and there is a greater propensity for dry eye ( ).

  
  
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  Lens wearers deemed or predicted to be poorly compliant with lens care regimens and wearing protocols may need to be seen more frequently in view of the link between noncompliant behaviours and adverse ocular reactions ( ).

  
  
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  A higher risk-taking personality style of contact lens wearers is associated with less compliant lens care behaviour ( ). Therefore lens wearers deemed to have a higher risk-taking personality may require more frequent aftercare visits.

  
  
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  Lens wearers displaying evidence of lens-induced pathology, or who are recovering from an adverse event, may need to be monitored more frequently, especially during the active or recovery phase of the condition ( ).

  
  
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  Following the initial 1-week check, neophyte wearers should be reexamined within the next 2 months in view of the high risk of discontinuation from lens wear in this demographic category ( ).

  
  
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  If lenses of a different type – or lenses of the same type but with modified parameters – are supplied to the patient, the aftercare schedule should be reset, with a visit after 1 week and further visits according to the decision matrix.

  
  
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  The decision matrix is largely designed for the review of asymptomatic, content contact lens wearers, notwithstanding that some patients might present with mild signs or symptoms that did not require urgent attention between aftercare visits. Patients should be explicitly advised to contact their eye-care practitioner if they have any questions or concerns about their comfort, vision or ocular health at any time.

  
  
• •
  

  The decision matrix sets out a time-line for ‘in person’ clinical aftercare examinations. Other forms of communication between practice and patient (for example, a phone call or e-mail from a member of support staff to enquire about ongoing lens performance) may also be useful, especially during the first few weeks of lens wear.

Patient Preparation and Time of Day of Examination

The potential for detecting problems that need to be addressed at a contact lens aftercare visit can be maximized by suggesting that the lens wearer synchronize lens usage leading up to the aftercare visit so that at the time of presentation to the practice, the lenses being worn are at the end of the replacement cycle. For example, a lens wearer using monthly replacement daily wear lenses should present with lenses that have been worn on a daily basis for one month.

As well, the examination of daily lens wearers is best conducted after at least 4 hours of lens wear on the day of the aftercare visit. Where there is overnight use of lenses, an early morning appointment is favoured – and again preferably towards the end of the life cycle of the lenses being worn – to potentially detect issues arising from closed eye lens wear. By scheduling aftercare appointments in this way, any problems with the integrity of the lens or ocular tissues, or deficits in vision or comfort, are more likely to manifest and can be addressed accordingly.

In-Practice Preparation

Certain in-practice preparations need to be made before the aftercare appointment. The previous record of the patient should be reviewed beforehand so that the practitioner can become familiar with the case history, anticipate any potential problems and devise an appropriate history-taking strategy. It is common practice that contact lens records for contact lens aftercare examinations are separate from the comprehensive examination encounter form, even within electronic medical record systems.

Efficient electronic patient records for contact lens practices will include separate forms for entry of contact lens parameters tried during the fitting as well visual and fitting results of trial and historical lenses. For example, efficient electronic records will allow the entry of comprehensive trial lens parameters with resulting vision, overrefraction and fitting data stored, with the option of a carry-forward of the dispensed trial lens parameters at the follow-up visits.

Data from a contact lens fitting or follow-up appointment may be retained separate or merged with typical encounter forms. All aftercare evaluations should record the recommended postfitting procedures including care solutions dispensed. Electronic systems may be preprogrammed with macros of common lens wear and care instructions for ease of selection and entry into the signed encounter note.

Before acquiring any patient-abstracted information, it is critical to include some patient demographics and appointment information. Along with patient names and identification numbers, age is an important variable to document, as this will assist in identifying presbyopic symptoms. The appointment date and time also should be noted; this data will probably be automatically recorded within electronic medical record systems. Date and time entry allow more accurate postexamination reviews if adverse reactions are noted at a certain time of day. For example, orthokeratology or rigid lens extended-wear patients typically are required to have initial extended-wear progress checks within 2 hours of awakening to monitor for lens adherence. Silicone hydrogel wearers should have initial progress checks within the first 2–4 hours of lens insertion to document any asymptomatic corneal staining induced by the unanticipated lens–solution interactions ( ).

Expected parameters of contact lenses worn to the aftercare visit should be at hand; these are typically carried over from the previous visit. This strategy is not always accurate because patients can present wearing ‘older’ lenses that are different to those prescribed at the most recent prior visit; lenses that have been obtained elsewhere (e.g. internet); or lenses that have become switched between the eyes; however, it affords an important point of reference during case history and compliance review.

A recent survey of eye-care practitioners around the world was performed to gather current practices for anterior eye health recording within examination records, and secondarily to provide the contact lens practitioner with guidelines on best practice ( ). The guidelines recommended the use of grading scales (discussed later), recording which grading scale is used, and grading to one decimal place. The tissue that has been examined should always be recorded, even if there are negative findings.

History Taking

The case history is crucial to assess patient compliance and to begin to formulate an opinion about the cause of any possible contact lens-related complications that have developed. The information obtained should include, at minimum, a subjective assessment of vision (including extent and duration of any morning or postlens removal blur), comfort, wearing time and care regimen. Additionally, it is important to elicit symptoms such as redness, tearing, photophobia or discharge if they are present. These series of questions are imperative to establish whether there is an incompatibility with the solutions or lenses.

It is good practice to review medications used by the patient and to ascertain whether any general allergic responses have been encountered, so as to ensure that these circumstances have not changed since the last visit. Additionally, patients can be invited to describe their chief complaint (if any) and review their overall lens-wearing history. A more detailed account of contact lens history taking can be found in Chapter 33 .

Visual Acuity

Presenting distance and near visual acuity with contact lenses should be recorded monocularly and binocularly with the consulting room lights on. This should be undertaken at each visit and the results compared with those expected from the dispensing visit or previous progress check. Visual acuity should be recorded prior to the utilization of any bright lights or disclosure dyes, which can induce lacrimation or lens misalignment.

Overrefraction

As with any subjective refraction, an initial objective assessment of refractive status using an autorefractor or retinoscope provides the starting point for the subjective overrefraction. Retinoscopy can also provide invaluable information when qualitatively viewing the red reflex over the lenses. Features such as optical zone edges or bifocal segments within the entrance pupil can be observed and correlated with patient reports of visual anomalies. Distortions or small visual obstructions induced from lens deposits, scratches, warped lenses or lens lift-off from the corneal surface may also be detected during over-retinoscopy. Lastly, ocular pathology of new onset since the last visit, such as a posterior subcapsular cataract, can be easily detected by viewing the red reflex.

A subjective sphero-cylindrical refraction over the contact lenses is an important measure that should be recorded at every visit. Overrefraction can reveal required power changes due to unanticipated lacrimal lens formations, lens rotation, changes in refractive error, patient-induced lens power changes, lens warpage or lens flexure. The duochrome test is especially useful in determining the refractive end-point of an eye wearing a contact lens.

A useful clinical technique during subjective refraction is to obtain both spherical and sphero-cylindrical end-points independently (rather than merely calculating the best-sphere refraction from the sphero-cylindrical end-point). In cases of spherical lens fitting, spherical power modifications can be demonstrated to the patient and the resultant visual acuity measured. If vision is inadequate following a spherical overrefraction, a sphero-cylindrical overrefraction should be performed and a toric lens fit initiated if warranted. In soft toric or rigid front-surface toric lens fitting, a sphero-cylindrical overrefraction can assist in determining the magnitude and direction of any cylinder mislocation ( ).

A repeatable cylindrical overrefraction obtained over a spherical rigid lens suggests lens flexure. Thin rigid lenses can flex approximately one-third of the corneal toricity. The probability of flexure increases with steeper and larger lenses. Flexure has been thought to increase with materials of higher oxygen permeability ( Dk ), but a study of rigid materials across a range of Dk values (from 15 to 151 Barrer) failed to find a difference in flexure when measured by overrefraction ( ).

Flexure can be confirmed by manual or automated keratometry over the lenses. A cylindrical overrefraction over a back toric rigid lens results from a crossed-cylinder effect and a careful review of the measured cylindrical power and axis suggests either over- or undercorrected cylindrical correction, misaligned cylinder axes or residual lenticular cylinder.

Overkeratometry

Corneal topography or keratometry performed while the lenses are worn will provide an index of lens flexure over a spherical rigid lens. As the anterior lens surface is being measured, the absolute instrument readings will not correlate with the baseline corneal measurements. The degree and location of the detected cylinder should correlate with the overrefraction if lens flexure is the suspected cause of residual astigmatism over a spherical lens on a toric cornea.

Assessing lens surface topography is believed by some practitioners to be a useful aid in determining the lens–cornea relationship in the soft lens fitting. When using keratometry, the clarity, consistency and shape of the mires that are reflected off the anterior soft lens surface can be useful for problem solving. For example, overkeratometry can help detect a steep or flat-fitting soft lens even though the lens fit may be judged to be clinically acceptable upon biomicroscopic examination. In a steep-fitting relationship, sustained overkeratometry observation can reveal distorted mires that become more irregular as the eye is left open between blinks. Additionally, the mire quality improves immediately after the blink when the lens has temporarily improved drapage over the cornea. In a flat fit, the opposite occurs: the mires blur immediately after blinking owing to excessive lens movement and the mire quality improves as the eye remains open and the lens stabilizes ( Fig. 37.2 ).

Appearance of keratometer mires reflecting off the surface of good, steep- and flat-fitting lenses, observed immediately before a blink, and immediately, 5 and 10 seconds after a blink.

External Examination

General inspection of the eye under an angle-poise lamp will reveal the presence of any general ocular pathology, such as red eye, conjunctival oedema or indeed almost any form of pathology, if severe enough. Also, evaluation of head posture, blink habits and palpebral aperture of the patient can provide important information on lens adaptation and lid effects. New rigid lens wearers often present with partial blinks or a narrowing of their palpebral aperture in an attempt to decrease lid sensations. Rigid contact lens wear has also been shown to induce true acquired nonsenile blepharoptosis from mechanical manipulation of the eyelids, or mild contact lens-induced lid inflammation (see Chapter 38 ).

Slit-Lamp Biomicroscopy

During the biomicroscopy evaluation while contact lenses are worn, the lens surface is first examined, followed by an evaluation of the lens fitting characteristics, and finally, an assessment is made of possible interactions between the lens and eye.

Lens Surface Assessment

Both rigid and soft lenses should be inspected for surface quality, deposit formation, tear film interactions and gross surface or edge defects. Clinically, it is very useful to observe the characteristics of the tear film and anterior lens surface between blinks. All soft lenses form mucoprotein deposits, which begin to form as soon as the lens is inserted. Tear film constituent deposition and coating are also expected; however, the analysis at this stage is aimed at determining whether the specific lens–cornea interaction in the patient being examined has resulted in the formation of a coating and, if it has, whether there has been any adverse reaction as a result. A decision can then be made as to whether the lens replacement frequency needs to be increased or a change of lens material is necessary.

The primary form of deposition on hydrogel lenses is mucoprotein. Silicone hydrogel lenses may develop an incompatible lipid deposition; it is estimated that there are more than 45 individual lipids within the tear film and the chemistry of the relatively hydrophobic silicone hydrogel materials may develop an incompatible lipid deposition ( ). Thus silicone hydrogel lenses should be closely observed for deposition even in the early refitting phase. Although these lenses deposit minimal amounts of protein ( ), about 13% of patients wearing silicone hydrogel lenses exhibit clinically significant lipid deposition on new lenses, even though they may not have had this problem with previous hydrogel materials ( ).

Although some care products are specifically formulated for use with silicone hydrogel lenses, there are conflicting findings (depending on the care product formulation, lens substrate and research methods) with respect to care products that have the ability to alter lipid sorption appreciably ( ); however, routine lens rubbing can remove small amounts of sorbed lipids that would otherwise tend to accumulate ( ).

Although it is clinically difficult to assess lens and tear film interactions, a biomicroscopy method for assessing tear break-up time using white light has been suggested. It is assumed that an intact and smooth tear film coating on the anterior surface of a lens (indicated by longer tear break-up times) enhances the biocompatibility of the lens and thus promotes comfort and tolerance. The patient is instructed to refrain from blinking and the examiner records the time to observe disruption of the tear film, as evidenced by a disruption of the white-light specular reflex from the anterior lens surface. Generally, break-up times of greater than 5 seconds should be observed on clean or mildly coated lenses. Break-up times of 4 seconds or less are usually associated with visible deposits and may indicate that the lens should be replaced more regularly or that the lens material is incompatible with the ocular surface of the patient ( ).

Obvious nonwetting of rigid lenses is easily detectable during the biomicroscopy evaluation and should correlate with patient symptoms of discomfort, hazy vision and the frequent need for lens removal and cleaning ( Fig. 37.3 ). Nonwetting of rigid lenses is common in patients with meibomian gland dysfunction (MGD). Patients may have worn rigid lenses successfully for years and used the same material and care products, yet find themselves with poor wetting lenses and difficulty managing comfort if the patient develops significant MGD.

Deposition on the surface of a rigid lens, presumed to be denatured protein.

Courtesy Kathy Dumbleton, Bausch & Lomb Slide Library.

The international workshop on MGD presented data suggesting that discomfort and dryness symptoms in contact lens wear are associated with MGD and management of the MGD can improve the symptoms ( ). Managing MGD and nonwetting in rigid lens wearers with lid hygiene, care solutions and material selection is achievable but can be challenging; often patients have to switch to hydrogels or suspend lens wear if the deposition cannot be managed. Other cases of nonwetting detected at aftercare visits may be secondary to organic compounds such as cosmetics or moisturizers, inappropriate lens care or adverse chemical interactions between incompatible solutions.

Rigid lens nonwetting is also occasionally noticed during lens dispensing; this immediate nonwetting is usually unrelated to MGD but may be due to improper preparation of the lens by the manufacturing laboratory that supplied the lens. Causes of manufacturing-related nonwetting include residual pitch and improper polishing.

Another lens surface change that should be assessed includes surface hazing. Symptoms caused by rigid lens surface hazing include lens dryness and variable vision; this problem is thought to be due to excess tear film evaporation from the anterior lens surface, resulting in surface drying. Surface hazing on rigid lenses soon after dispensing may be an indication to change the lens material. In general, silicone acrylate and fluorosilicone acrylate materials behave differently, with the latter exhibiting greater tear film retention. Lastly, surface scratches and calcified deposits are common on aged lenses. As lens polishing is not routinely carried out in optometry practices today, these findings typically dictate lens replacement.

Lens Fitting Characteristics

Lens movement and centration should be evaluated as described in Chapter 8, Chapter 15 for soft and rigid lenses, respectively. Deviations from the initially desired fitting approach should be assessed and changes made to lens parameters as needed. However, practitioners should anticipate the possibility of a slight alteration of in-eye hydrogel lens performance towards the end of each day, as the lens dehydrates ( ). Hydrogel lens fitting may also alter towards the end of the wearing cycle of reusable soft lenses. This is due to an ‘ageing effect’, whereby there is a gradual loss of water over the life of the lens ( ). This water loss can possibly alter the lens dimensions and have an impact on lens movement and comfort.

For rigid lenses, a fluorescein pattern evaluation should always be performed, with either the Burton lamp or the slit-lamp biomicroscope, or both. It should be noted that with the Burton lamp it is not possible to observe the fluorescein patterns of rigid lenses made from materials that absorb ultraviolet light. When the slit-lamp biomicroscope is used, the appearance of the fluorescein pattern can be enhanced by introducing a cobalt blue filter into the illumination system and a yellow barrier filter (Wratten number 12 yellow) into the observation system.

The fluorescein pattern should be assessed at every routine rigid lens aftercare visit to establish whether the lens fit has changed. At the first aftercare visit, fluorescein pattern interpretations can vary as patients adapt to their lenses and reflex tearing subsides. It is not uncommon for a lens to be judged to be fit with apical clearance at a dispensing visit, yet be observed to be fit with apical touch at a progress evaluation ( Fig. 37.4 ).

(A) Rigid lens fluorescein pattern at initial lens dispensing, showing apical clearance. (B) Same patient and lens as in (A), seen at an aftercare visit 2 weeks later, after adapting somewhat to lens wear. Note that mild corneal touch is now evident; this may have been masked by excessive tearing during lens fitting.

Scleral and corneo-scleral lenses should be assessed without fluorescein first to check for conjunctival blanching and posttear lens thickness. Tear layer thickness can be assessed with a parallelopiped slit-lamp beam; the gap between the posterior lens surface and the anterior cornea can be judged in relation to the known corneal or lens thickness using white light. Fluorescein can then be added to assess tear exchange and flow beneath the lens surface.

Because the corneal shape and posterior lens tear film thickness may change as the patient adapts to new scleral lenses (which will influence the interpretation of the lens fit), it is wise not to alter lens parameters until the fitting has stabilized, typically about 2 weeks after lens fitting. Scleral lens settling is known to change the posterior tear film thickness dramatically once the patient has adapted ( ). Over an 8-hour time span, lenses can settle by about 100 μm; therefore lens changes made for tear clearance on the initial dispensing day may not be accurate. The lenses should be sufficiently settled after a few weeks, and then, patients should present at least 2 hours after lens insertion for the aftercare visits.

Lens–Eye Interactions

With the lens in the eye, there is an opportunity to look for any adverse interactions between the lens and ocular surface. In the case of 3 and 9 o’clock corneal staining, the tissue compromise would be expected to be aligned with the position of the lateral edges of a rigid lens. In the context of lens fitting, the peripheral profile of a rigid lens may appear steeper at a follow-up visit than was initially documented once reflex tearing has subsided; this can be detected by insufficient edge clearance, peripheral seal-off or even an epithelial indentation ring ( Fig. 37.5 ).

Epithelial indentation ring immediately following lens removal, revealed with the aid of fluorescein, indicating an extremely steep-fitting lens and/or a strongly adherent lens.

A conjunctival indentation ring induced by a tight-fitting soft lens would be expected to coincide with the position of the lens circumference. Higher-modulus silicone hydrogel lenses may also create asymptomatic conjunctival imprints, circumferential conjunctival staining, or conjunctival flaps at the edge of the lens. Corneal staining induced by a lens defect is likely to be observed in the proximity of that defect. It would be difficult to reconcile many of the adverse reactions described above with lens performance and location if these reactions were first detected after the lens had been removed.

Uncorrected Vision

An initial measure of uncorrected vision can be reconciled against the presenting visual acuity, the magnitude and nature of the refractive error and the subsequent subjective refraction. It should be noted that vision may be significantly degraded – beyond that attributable to uncorrected refractive error – during the first 15 minutes following lens removal. This is due to the fact that the tear layer is disrupted following lens removal, which can take about 15 minutes to recover ( ).

Refraction

Aside from natural changes in refractive error unrelated to lens wear, contact lens-induced alterations in corneal curvature can significantly alter refractive error with associated changes in visual acuity. An autorefractor or retinoscope should be used initially to determine refractive status prior to undertaking a subjective refraction. Retinoscopy has the added advantage of facilitating direct observation of the optical quality of the eye, the detection of ocular aberrations or distortions induced by the contact lens.

Refractive error should be expected to remain constant or to progress slowly over time and should be unaffected by lens wear. Also, visual acuity should remain correctable to prefitting levels. Reduced visual acuity may signal the presence of ocular pathology or lens-induced warpage if it correlates with corneal curvature changes, as described later in this chapter. An average of a one-line decrease in best corrected visual acuity attributable to contact lens-induced topographic abnormalities has been reported ( ).

Specific refractive error changes have been documented with certain lens types and wearing schedules. Myopic progression associated with daily wear of hydrogel lenses with low oxygen permeability was reported in early clinical trials ( ). An average of 0.30 D increase in myopia has been reported after 9 months of extended wear of low- Dk soft lenses, which was presumably due to hypoxia-driven corneal oedema ( ). Conversely, extended wear with high-modulus silicone hydrogel materials has no impact on refractive error and may even be associated with a hyperopic shift from central corneal flattening in some patients ( ). In fact, orthokeratology-like induced topographic changes have been documented with high-modulus silicone hydrogel lenses that are typically of high powers and/or being worn inside out ( ).

Refractive error changes have been reported in adult patients who have monocular blur intentionally induced with monovision contact lens correction. Specifically, approximately one-third of patients can expect changes in anisometropia between 0.50 and 1.25 D after wearing monovision contact lenses ( ).

Keratometry and Corneal Topography

Corneal shape changes and/or warpage may appear with any type of contact lens secondary to mechanical stress or lens interference with corneal metabolism ( ). Corneal shape changes are rare in uncomplicated soft lens wear ( ).

It is important to be able to identify rigid lens-induced corneal changes correctly before they create severe visual consequences. Also, careful corneal curvature assessment is a good predictor of lens fit and physiology. Corneal topography or keratometry may reveal numerical changes from the prefitting values, or an increase or decrease in corneal astigmatism.

A general consensus is that, in normal eyes, changes greater than ±1.00 D from baseline are clinically significant, and in such cases, the fit should be investigated for potential alteration to prevent potentially long-term corneal moulding. In eyes with pathology such as keratoconus or postcorneal transplantation, large changes in keratometry readings are not uncommon. Increased corneal astigmatism or curvature changes in keratoconus indicate progression of the disease and in postcorneal transplant patients indicate continued wound healing, recurrent disease (if the transplant was performed for keratoconus) or instability of the host cornea. Large changes in corneal astigmatism can be detected in keratoconus patients posttransplant, beginning about a decade after surgery ( ); therefore continued measurement of keratometry or topography is prudent in these patients. Keratometry can detect surface irregularity by assessment of mire distortion. In fact, the quality of the mires should be graded at every progress check (see Appendix K ).

A superior technique for assessing changes in corneal curvature is to undertake a corneal topographic assessment. One of the most valuable applications of this technology is to monitor the stability of the cornea after both short- and long-term lens wear. Subtle corneal steepening or sphericalization that is undetectable with keratometry may characterize early corneal changes due to contact lens wear. Serial topography assessment with the use of topographic difference maps may reveal subtle changes over time.

Occasionally, rigid contact lenses can distort the corneal surface, resulting in transient or permanent corneal warpage. Most forms of distortion can be traced back to the fit and/or material of the lens. Different forms of corneal distortion can be detected and often can be classified into one of three categories: (1) a shift from a prolate to an oblate shape, (2) inferior corneal steepening or (3) ‘smile’ impression arcs.

used profilometry and topography-based corneo-scleral limbal radius estimates to quantify the effect of 5 hours of cornea-scleral contact lens wear on the anterior eye surface of healthy eyes, including cornea, corneo-scleral junction and sclero-conjuctival area. Although the authors did not observe any corneal shape changes, they observed alterations to sclero-conjuctival topography in the form of sclero-conjuctival flattening which was not uniformly distributed across the anterior eye.

Oblate Shape

The normal cornea is a prolate shape: it is steeper in the centre and flattens aspherically in the periphery. Long-term flat-fitting rigid lenses can permanently shift the cornea to an oblate shape by flattening the central cornea and secondarily steepening the periphery. This type of warpage may not be detected with keratometry or manifest refraction if the astigmatism is regular and the patient remains correctable to 6/6. Only corneal topographic assessment can reveal the oblate shape, which can create difficulty in rigid lens fitting and problem solving.

As mentioned previously, silicone hydrogel lenses can induce a transient oblate corneal shape and a related decrease in myopia. Fig. 37.6 shows an example of this phenomenon, where a high myope wore a high-modulus silicone hydrogel lens for 30-day continuous wear, and 3 months after entering this mode of wear, central corneal flattening and 1.00 D of decreased myopia were detected.

Oblate corneal shape induced unintentionally in a lotrafilcon A extended-wear contact lens user.

Inferior Steepening

Long-term wear of low- Dk rigid lenses or superiorly decentred rigid lenses can cause inferior corneal steeping and give the appearance of keratoconus ( Fig. 37.7 ).

Inferior corneal steepening secondary to corneal warpage from long-term rigid lens wear.

Courtesy Leon Davids, Bausch & Lomb Slide Library.

compared the topography findings of 100 eyes with either keratoconus or contact lens-induced warpage. They concluded that keratoconic eyes have high shape factors, extremely high corneal irregularity measures and steep toric mean reference curvatures, whereas contact lens-induced warpage is characterized by almost-spherical shape factors, elevated corneal irregularity measures and normal toric mean reference curvatures.

Even soft lenses can cause severe shape changes, which are often due to hypoxia-induced corneal swelling, and which can also give the appearance of inferior corneal steepening and pseudokeratoconus. Fig. 37.8A shows the topography of a patient after sleeping in group 4 hydrogel lenses on a weekly basis for 6 months. Note the inferior steepening, which mimics keratoconus. After discontinuing all lens wear, corneal topography normalized in 3 weeks ( Fig. 37.8B ).

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1. Anterior Eye
2. History Taking
3. Practice Management
4. Diagnostic Instruments

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