KEY POINTS
RGP CLs are the most common visual rehabilitation option to improve keratoconic patients’ quality of life.
The use of this CPG can guide clinicians in the process of fitting RGP CLs in patients with keratoconus.
The CPG provides evidence-based information to support clinical decisions in keratoconic patient management.
INTRODUCTION
Keratoconus is a progressive, bilateral and often asymmetric corneal disorder characterized by thinning and steepening of the central and paracentral cornea that causes high myopia and irregular astigmatism [1–3] [1,2] [4] [5,6]
Rigid gas permeable contact lenses (RGP CLs) provide a tear layer between the irregular corneal surface and the contact lens and thus provide excellent vision for patients with keratoconus and improve patients’ quality of life [1,5–7] [8] [9] [8,10,11] [10–15]
Clinical practice guidelines (CPGs) are defined as statements that are informed by a systematic review of the evidence to assist practitioners in making clinical, policy-related and system-related decisions [16,17] [18]
The purpose of this review is to evaluate the existing literature to create CPGs that provide eye care practitioners with a strategy to successfully fit RGP CLs in patients with keratoconus. The CPG was appraised by eight independent expert panelists using the Appraisal of Guidelines for Research and Evaluation (AGREE II) [18]
LITERATURE REVIEW
An extensive search of databases [Medline, PubMed, Google Scholar, Science Direct, Cochrane, metaRegister of Controlled Trials (www.controlled-trials.com www.clinicaltrials.gov
KEY TO EVIDENCE STATEMENTS AND RECOMMENDATIONS
Based on review of the 52 published articles, a collection of key statements and recommendations were created by the CPG development group (Table 1 ). The classification of recommendations was determined by considering two, widely adopted grading systems. Namely, the Scottish Intercollegiate Guidelines Network (SIGN) [19] [20–24]
Table 1 -
Key rigid gas permeable contact lenses care and fit recommendations in keratoconus
Statement
Key recommendations for care
Grades of recommendations (GRADE system)
Levels of evidence (SIGN system)
RGP CLs are the most common choice for visual rehabilitation of a patient with keratoconus
SR
GQ
II++
RGP CL fitting in keratoconic patients should take place in three visits: initial or diagnostic visit, dispensing visit and prescribing visit
DR
MQ
II−
The use of Calculens.com to determine the first diagnostic RGP lens allows a reduction in the number of trials and visits necessary to achieve a successful RGP CL fitting in keratoconus
SR
GQ
II+
The ‘three-point-touch’ (divided support) pattern is the most widely accepted and safest modality of RGP CL fitting in keratoconus
SR
GQ
I−
Apply changes of BOZR in steps of 0.10 mm to refine fluorescein pattern until 3-point-touch fluorescein pattern is achieved
DR
MQ
III
Patient education in the correct maintenance and handling of RGP CLs and hand hygiene is essential in reducing CL complications and adverse effects
SR
GQ
II−
After dispensing the RGP CLs, a wearing schedule starting with 1–2 h/day and adding 1–2 h/day until 8–12 h/day is achieved, during the 2–3 weeks before the prescribing visit
GPP, DR
LQ
IV
During first year of RGP CLs wear keratoconic patients should be checked every 3 months. After this, visits every 6 months should be acceptable (with biomicroscopy, fluorescein pattern assessment and corneal topography)
GPP, DR
MQ
IV
Keratoconus patients should be advised to remove their RGP CLs whenever redness, tearing, visual loss or pain occurs and to consult their eye-care professional at once
SR
GQ
IV
Levels of evidence (SIGN system): I++ high-quality meta-analyses, systematic reviews of RCTs or RCTs with a very low risk of bias; I+ well conducted meta-analyses, systematic reviews of RCTs or RCTs with a low risk of bias; I− meta-analyses, systematic reviews of RCTs or RCTs with a high risk of bias; II++ high-quality systematic reviews of case–control or cohort studies and high-quality case–control or cohort studies with a very low risk of confounding or bias and a high probability that the relationship is causal; II+ well conducted case–control or cohort studies with a low risk of confounding, bias or chance and a moderate probability that the relationship is causal; II− case–control or cohort studies with a high risk of confounding, bias or chance and a significant risk that the relationship is not causal; III nonanalytical studies, e.g. case reports, case series; IV evidence obtained from expert committee reports or experts’ opinion.Grade of recommendation (Grading of Recommendations Assessment, Development, and Evaluation system): GQ, good quality: further research is very unlikely to change our confidence in the estimate of the effect; MQ, moderate quality: further research is likely to have an important impact on our confidence in the estimate of the effect and may change the estimate; LQ, low quality: further research is very likely to have an important impact on our confidence in the estimate of the effect and is likely to change the estimate; SR, strong recommendation: interventions that ‘should’ be used, the guidelines development group is confident that, for the vast majority of people, the intervention (or interventions) will do more good than harm; DR, discretionary recommendation: should be ‘considered’, the guidelines development group is confident that the intervention will do more good than harm for most patients. GPP, Good-practice points: Recommended best practice is based on the clinical experience of the guideline development group.RGP CL, rigid gas permeable contact lens; BOZR, back optic zone radius; GRADE, Grading of Recommendations Assessment, Development, and Evaluation; SIGN, Scottish Intercollegiate Guidelines Network; RCT, randomized controlled trial.
SIGN is a revised system of determining levels of evidence based on study design and the methodological quality of individual studies. SIGN define four levels of evidence (from I to IV): I++ high-quality meta-analyses, systematic reviews of randomized controlled trials (RCTs) or RCTs with a very low risk of bias; I+ well conducted meta-analyses, systematic reviews of RCTs or RCTs with a low risk of bias; I− meta-analyses, systematic reviews of RCTs or RCTs with a high risk of bias; II++ high-quality systematic reviews of case–control or cohort studies and high-quality case–control or cohort studies with a very low risk of confounding or bias and a high probability that the relationship is causal; II+ well conducted case–control or cohort studies with a low risk of confounding, bias or chance and a moderate probability that the relationship is causal; II− case–control or cohort studies with a high risk of confounding, bias or chance and a significant risk that the relationship is not causal; III Nonanalytical studies, for example case reports, case series; IV evidence obtained from expert committee reports or experts’ opinion.
GRADE is a system that provides rating quality of evidence and strength of recommendations [20–24]
Each recommendation is assigned an overall strength: strong recommendation, discretionary, weak or conditional recommendation and good practice point (GPP) – according with SIGN and GRADE recommendations – strong recommendation are interventions that ‘should’ be implemented. The CPG development group is confident that, for the vast majority of people, the intervention (or interventions) will do more good than harm. Discretionary recommendation should be ‘considered’. The CPG development group is confident that the intervention probably will do more good than harm for most patients. GPP are recommended best practice based on the clinical experience of the guideline development group.
Some recommendations can be made with more certainty than others. The wording used in the recommendations in CPG denotes the certainty with which the recommendation is made (the ‘strength’ of the recommendation). The ‘strength’ of a recommendation considers the quality (level) of the evidence. Although higher quality evidence is more likely to be associated with strong recommendations than lower-quality evidence, a particular level of quality does not automatically lead to a particular strength of recommendation.
GUIDELINES DEVELOPMENT (APPRAISAL OF GUIDELINES FOR RESEARCH AND EVALUATION II INSTRUMENT AND EXPERT PANEL PARTICIPATION)
The AGREE II is a well validated tool used to assess the quality of CPG [18,25,26] Table 2 ) [18] [18] [27,28] [18] [29–31] [32] [33–34] [35] [36]
Table 2 -
Appraisal of Guidelines for Research and Evaluation II domains and items
Domain 1: Scope and purpose
 1
The overall objective(s) of the guideline is (are) specifically described
 2
The health question(s) covered by the guideline is (are) specifically described
 3
The population (patients, public, etc.) to whom the guideline is meant to apply is specifically described
Domain 2: Stakeholder involvement
 4
The guideline development group includes individuals from all relevant professional groups
 5
The views and preferences of the target population (patients, public, etc) have been sought
 6
The target users of the guideline are clearly defined
Domain 3: Rigour of development
 7
Systematic methods were used to search for evidence
 8
The criteria for selecting the evidence are clearly described
 9
The strengths and limitations of the body of evidence are clearly described
 10
The methods for formulating the recommendations are clearly described
 11
The health benefits, side effects and risks have been considered in formulating the recommendations
 12
There is an explicit link between the recommendations and the supporting evidence
 13
The guideline has been externally reviewed by experts prior to this publication
 14
A procedure for updating the guideline is provided
Domain 4: Clarity of presentation
 15
The recommendations are specific and unambiguous
 16
The different options for management of the condition or health issues are clearly presented
 17
Key recommendations are easily identifiable
Domain 5: Applicability
 18
The guideline describes facilitators and barriers to its application
 19
The guideline provides advice and/or tools on how the recommendations can be put into practice
 20
The potential resource implications of applying the recommendations have been considered
 21
The guideline presents monitoring and/or auditing criteria
Domain 6: Editorial independence
 22
The views of the funding body have not influenced the content of the guideline
 23
Competing interests of guideline development group members have been recorded and addressed
Overall assessment
Judgement as to the quality of the guideline, taking into account the criteria considered in the assessment process
Provide a recommendation for use of the guideline
After the development of the CPG for fitting RGP CLs in keratoconic patients, the guidelines were reviewed using the AGREE II instrument requirements (Table 3 ) by an international panel of eight independent experts (Keratoconus Guideline Appraisal Group), each of whom have wide experience in RGP CL fitting in keratoconus. The experts on the panel hail from Australia (one), Italy (one), Portugal (one), Spain (three), the Netherlands (one) and the United Kingdom (one). For each domain evaluated, the experts’ mean AGREE II score exceeded the 60% value that is considered as a sufficient to recommend the use of the CPG (Fig. 1 ) [30,37,38]
Table 3 -
Summary of Appraisal of Guidelines for Research and Evaluation II instrument evaluation scores for each domain achieved by expert panel
AGREE II domain
Mean ± SD (%)
Median (%)
Mode (%)
1. Scope and purpose
88.88 ± 14.70
91.50
100.00
2. Stakeholder involvement
73.63 ± 12.42
69.50
61.00
3. Rigor of development
83.75 ± 11.49
86.50
63.00
4. Clarity of presentation
88.75 ± 6.02
89.00
83.00
5. Applicability
72.38 ± 22.58
79.00
58.00
6. Editorial independence
87.50 ± 35.35
100.00
100.00
Overall assessment
85.42 ± 10.68
83.33
83.00
AGREE II, Appraisal of Guidelines for Research and Evaluation II.
FIGURE 1: Box plot of the Appraisal of Guidelines for Research and Evaluation II domain scores across the eight expert panel members. Boxes represent interquartile range (Q 1–Q 3) with the median (Q 2) represented as a horizontal line. Whisker lines represent distance between the smallest and the largest value. Outliers are plotted as circles when they differ from the median by more than 1.5Ă— of the interquartile range. Extreme values are plotted with an asterisk (∗) when they differ from the median by more than 3Ă— the interquartile range.
CLINICAL PRACTICE GUIDELINES FOR FITTING KERATOCONUS PATIENT WITH RIGID GAS PERMEABLE CONTACT LENS
The CPG developed includes nine key recommendations (Table 1 ) that outlines a strategy for successfully fitting RGP CLs in keratoconic patients. For each key recommendation discussed, we include in parenthesis the strength of the recommendation as per the CPG development group (strong recommendation, discretionary recommendation or GPP), and the strength of evidence per the GRADE (good or high quality, moderate quality, low quality or VLQ) and SIGN systems (levels I through IV). This takes place in three different visits (discretionary recommendation; moderate quality; II− ): the initial or diagnostic visit, dispensing visit and prescribing visit (Fig. 2 ). The practitioner's aim is to prescribe a RGP CL that induces minimal mechanical impact on the corneal surface while providing excellent patient comfort and visual rehabilitation (strong recommendation; good or high quality; II++ ). The CPG discusses these visits in detail, including how to calculate contact lens parameters, how to evaluate optimal contact lens fit, and guidance on patient education and follow-up.
FIGURE 2: Flow chart outlining protocol for successful rigid gas permeable contact lens fitting in patients with keratoconus.
SCHEDULE AND GAS PERMEABLE FITTING CLINICAL PROCEDURE
1.- Initial or diagnostic visit
During the initial visit the clinical provider should obtain a full history and conduct a complete ophthalmic exam. The patient will be asked structured questions regarding the reason for the visit, the nature of the presenting problem, their visual and ocular history, general health, medication and allergies, their family ocular and medical histories as well as vocational visual requirements [39]
A complete eye examination should be conducted to determine whether the patient is a good candidate for contact lens wear [40] [41,42] [41,42]
If, based on the history and exam, the patient is a good candidate for RGP CLs, the eye care provider should discuss wearing schedule, replacement frequency, financial cost and the care required for contact lens hygiene. If the patient accepts RGP CL wear and is interested in proceeding, the next step is to calculate the parameters of the diagnostic RGP CL [base-optic zone radius (BOZR), periphery and total diameter].
Calculation of the first diagnostic lens parameters
There are multiple manufacturers and companies that provide RGP CLs with specific keratoconus designs. Most of them come with a trial set, which allows more than one diagnostic lens to be fitted in the same session. Use of trial set requires adequate disinfecting and maintaining of the lenses, for example with use of hydrogen peroxide or povidone iodine solutions. These solutions have been found to be effective against bacterial, fungi, amoebae and virus (herpes simplex, HIV and coronaviruses) [43]
This guideline recommends using measured keratometry or simulated keratometry (provided after corneal topography assessment) and Calculens.com (www.calculens.com [44,45] [44,45] [44] + ).
First diagnostic lens assessment
The first diagnostic RGP lens is selected from a trial set, based on the suggested parameters. Usually, the RGP trial set has lenses with the same power and a standard diameter but different BOZR. The first RGP diagnostic contact lens calculated is inserted into the patient's eye and the eye care practitioner must allow the diagnostic RGP CL is placed on the patient's ocular surface and allowed to settle for 20–30 min [11,46,47] [48] [49]
After 20–30 min of wear, the practitioner should evaluate the diagnostic contact lens to ensure optimal static and dynamic fit [50,51] [49,50]
The diagnostic contact lens should also be assessed for adequate movement with blinking. Slight movement is needed to allow tear exchange under the lens with each blink. However, excessive movement can result in patient discomfort and fluctuations in vision.
The practitioner should assess for any interaction between the RGP CL and the eyelid. Specifically, eyelid attachment or interpalpebral fitting to provide adequate lens positioning, stability and centration [47]
The diameter of the contact lens should be evaluated to ensure it completely covers the pupillary aperture. If total diameter is modified additional BOZR adjustments should be necessary to guarantee the lens sagittal height remains the same.
Lastly, the fluorescein pattern is assessed with a slit-lamp using a cobalt filter and a Wratten 12 or Tiffen 2 yellow filter [52] [53] [54] [55] [55,56] Fig. 3 ) (strong recommendation; good or high quality; I− ). In this fitting philosophy the RGP CL has light touch on the apex with peripheral alignment. Lens support and bearing is shared between the apex and the paracentral cornea.
FIGURE 3: Fluorescein patterns of the three fitting philosophies. (a) Apical touch; (b) three-point-touch; (c) apical clearance.
Central flat (apical touch) or steep (apical clearance) fluorescein patterns indicate that the BOZR must be changed. If any parameter of the diagnostic lens is inadequate, the RGP CL must be changed and a second diagnostic lens selected. It is advised that adjustments to the BOZR are made in steps of 0.10 mm or greater (discretionary recommendation; moderate quality; III); for example, the next diagnostic lens is decreased by 0.10 mm steps if the BOZR of the lens was too flat and vice versa [57] Fig. 4 ). Special attention should be paid to the mid-peripheral fluorescein pattern because mid-peripheral alignment is necessary to avoid a flat or tight lens fit. Finally, correct peripheral alignment with a narrow band of edge clearance at the periphery is recommended to enable adequate tear exchange and comfort, avoiding an excess or reduced edge clearance.
FIGURE 4: Flow chart of diagnostic lens selection and back optic zone radius evaluation at the first diagnostic visit. BOZR, back optic zone radius; RGP, rigid gas permeable.
Once the BOZR and peripheral design are determined, over-refraction should be performed to determine the power of the RGP lens and the best corrected visual acuity (BCVA) and the RGP lens will be ordered from the manufacturer.
2.- Dispensing visit
During the dispensing visit, the ordered RGP CL should first be evaluated to ensure the lens is free from defects and that all parameters are within acceptable tolerances [46]
The RGP CL is then evaluated on the patient's ocular surface to ensure the lens displays correct movement, centration, fluorescein pattern and provides excellent vision.
If the RGP CL satisfies the criteria above, the eye care practitioner may dispense the contact lens with a wearing schedule starting with 1–2 h on the first day and then adding 1–2 h/day until a minimum of eight hours of wear each day (with a maximum of 12 h/day) is achieved in new RGP CLs wearers (discretionary recommendation; low quality; IV; GPP). It is suggested that the 12-h maximum wearing period is not exceeded until the eye care practitioner has assessed the fit in the prescribing visit and provides the information about normal adaptive symptoms and signs.
Patient education
The patient should be trained in the care, maintenance and handling of RGP CLs [58,59] − ). This includes hand hygiene, how to disinfect and store lenses with appropriate solutions, methods for insertion and removal, and safe wearing practices [59]
3.- Prescribing visit
The purpose of the prescribing visit is to guarantee that the dispensed RGP CL is correct in terms of visual acuity, comfort, fitting and safe without contact lens-related complications. After 2–3 weeks of wear the RGP contact lens fit should be assessed considering lens movement, centration and fluorescein pattern, vision and ocular surface health. The RGP CL fit is considered to be good if all these conditions are acceptable: the RGP CL provides good vision that cannot be improved with over-refraction, enough comfortable daily wear (minimum of 8 h/day or more) and optimal physiology of ocular surface without contact lens-related complications such as corneal staining, hyperemia, keratitis, giant papillary conjunctivitis or others. The eye care practitioner must provide follow-up recommendations and a schedule of aftercare visits.
If any parameter of the RGP fit is found to be inadequate, a new RGP CL should be ordered and a new dispensing visit should be scheduled. If, after multiple visits a satisfactory RGP CL fit cannot be achieved, the eye care practitioner should consider other contact lens options such as scleral lenses, hybrid lenses or piggy back systems as well as noncontact lens-related options (surgical management) [1,2,5,6]
4.- Follow-up visits
During the first year of RGP CL wear, follow-up visits should occur every 3 months (discretionary recommendation; moderate quality; IV; GPP). After the first year, visits every 6 months should be acceptable (discretionary recommendation; moderate quality; IV; GPP). As always, modifications should be made specific to the clinical context. More frequent visits may be appropriate in patients with higher risk of keratoconus progression or concurrent anterior segment disease and the eye care practitioner should recommend additional visits whenever the patient experiences an unexpected problem in vision or ocular condition (strong recommendation; good or high quality; IV). Visit frequency may decrease in subsequent years depending on the severity of the disease and case evolution. At all follow-up visits, the eye care practitioner must check the visual acuity with RGP lens, comfort, over-refraction, corneal topography, RGP lens surface (e.g. polishing, scratches, chips, fogging) and fit assessment with fluorescein (attention should be paid to the apical touch and changes in the fluorescein pattern, which can be indicative of keratoconus progression and a requirement for refitting of the RGP CL) [52]
In addition, the eye care practitioner should regularly check corneal topography and/or tomography. Topography provides valuable information about the anterior corneal surface, including corneal warpage from contact lens use and keratoconus progression. Of note, accurate monitoring of keratoconus progression using topography will require a contact lens holiday of several weeks preceding the visit. This may be burdensome for those patients who rely on contact lenses for functional vision. For these patients, tomography can be especially valuable since keratoconus progression can be monitored by changes in posterior surface steepening and global thickness pattern [2]
Common findings in aftercare visits
RGP CL wear can lead to induced astigmatism of the anterior corneal surface (warpage), that results in a reversible loss of visual acuity [60] [61]
There are a number of different causes of corneal staining that may be observed. For instance, apical staining can occur if the RGP CL is too flat with apical touch and excessive lens movement. Constant irritation of the flat RGP CL may lead to scarring. To manage this problem, it is necessary to decrease the pressure of the RGP lens on the apex of the cone (refit the RGP CL with a steeper BOZR) [60] [60] [62]
CONCLUSION
This CPG was developed based on review of the available evidence and validated using AGREE II by eight independent expert panelists. Use of this CPG in clinical practice provides clinicians with a successful strategy for fitting RGP contact lenses in patients with keratoconus.
Keratoconus Guideline Appraisal Group is formed by: Victoria de Juan (University of Valladolid; Hospital Universitario RamĂ³n y Cajal, Madrid, Spain) Luisa Simo (Plymouth University, United Kingdom), Cesar Villa-Collar (Universidad Europea de Madrid, Spain); David Piñero (Universidad de Alicante, Spain); Gonzalo Carracedo (Universidad Complutense de Madrid, Spain); JosĂ© Manuel Gonzalez-Meijome (Universidade do Minho, Portugal); Lily Ho (University of New South Wales, Australia); Giancarlo Montani (UniversitĂ¡ del Salento, Italy); Henny Otten (Visser Contactlenzenpraktijk, The Netherlands) and Gary Orriss (Orriss & Low Optometrists, United Kingdom).
Acknowledgements
We would like to thank to Keratoconus Guideline Appraisal Group for their collaboration appraising and improving CPG.
Financial support and sponsorship
The current work was supported by the Optometry Research Group, IOBA Eye Institute (University of Valladolid) Valladolid (Spain).
Conflicts of interest
None of the authors has a financial or proprietary interest in any material or method mentioned.
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