May 1, 2023
By Monica Jong, BOptom, PhD, Global Director of Professional Education, Myopia, Johnson & Johnson Vision
Topography has been suggested as the gold standard for orthokeratology fitting because the detailed mapping of the cornea allows more accurate fitting and a custom-made lens.
Myopia is one of the greatest eye health threats of the 21st century.1 By 2050, the prevalence of myopia will reach 50% without accounting for the three time increase in myopia that occurred in parts of the world during the COVID-19 lockdowns.2 Today, professional associations such as the World Council of Optometry, the American Academy of Optometry, and the American Academy of Ophthalmology recognize that myopia management should be the standard of care.3-5
Practitioners today have the ability to provide patients with options matched to the patient’s clinical and lifestyle factors.6 Orthokeratology may be a good option for those who would like to manage myopia or be completely lens free during the day.7 Patients who have previously suffered from soft contact-lens-related discomfort or dryness may also benefit.8 Orthokeratology can generally fit myopes up to -4.50D and -1.50D of astigmatism.7
Orthokeratology has been demonstrated to be one of the most effective treatments for myopia management, with up to ten years of studies.9-11 Advancements in corneal topography alongside new experiential guided fitting software can revolutionize the way we fit orthokeratology. Accurate corneal maps may help achieve the optimum lens fit.
There are generally four distinct zones that define the geometry of an orthokeratology lens design (Figure 1A):7
- Base Curve (BC): The base curve flattens the central cornea to achieve the refractive correction for the patient.
- Reverse Curve (RC): The reverse curve is the second curve on the lens and it is dramatically steeper than the base curve in order to bring the lens back down towards the cornea.
- Tangent Zone (TZ) = Alignment Curve: The tangent zone’s main purpose is to align the lens to the cornea and keep the lens centered on the eye to achieve the desired orthokeratology effect.
- Edge Lift (EL) = Peripheral Curve: The edge lift is the thin zone in the peripheral curvature of the lens and provides comfort as the lens sits on the eye and promotes exchange of tears.
The sagittal height (often referred to as “sag height”) is the depth from the corneal apex to a more peripheral measurement location on the cornea. Matching the depth of the lens to this location on its tangential zone to match the sag height of the cornea to be fitted will more likely result in a good fit.7
Importance of Topography in Orthokeratology
Topography has been suggested as the gold standard for orthokeratology fitting because the detailed mapping of the cornea allows more accurate fitting7 and a custom-made lens.13 Topography is essential for pre- and post-follow-up.9
The two most common corneal mapping systems are Placido ring technology and Scheimpflug tomography. These construct a three-dimensional model of the anterior corneal surface.
- Placido ring topographers analyze rings that are reflected off the corneal surface.14
- Scheimpflug imaging is generated by a rotating Scheimpflug camera used to locate the anterior and posterior corneal surfaces.14
Topography in Action — Diagnostic vs. Guided Experiential Fitting
Diagnostic fitting involves using trial lenses to assess fit. A trial lens is selected based on patient corneal measurements, and typically the same lens is worn overnight to assess corneal reshaping the next day. A clinical study reported that in a group of experienced orthokeratology practitioners, fluorescein pattern analysis alone did not improve the clinical assessment of fits versus the first trial lens fit from topography measurements.12
Experiential guided fitting software, a type of empirical fitting, is enabling more practitioners to include orthokeratology in their myopia management portfolio by making orthokeratology easier and simpler:
- For example, the FitAbiliti software from Johnson & Johnson Vision is an all-in-one experiential guided fitting software that walks the practitioner through all the required tests, simulates the lens on the eye based on the patient’s clinical and topography data, and then automatically orders the lens.†
- The customized lens then arrives and is delivered to the patient by the practitioner to commence overnight lens wear.
- At the first and subsequent follow-up visits, the software guides the practitioner through analyzing the orthokeratology-lens-induced changes on the corneal topography maps, supporting the practitioner every step of the way.†
- FitAbiliti has a 90%* first time fit success rate.15§ It may also reduce chair time since the lens order is done automatically and there is no need to store or clean any diagnostic lenses in the office.
Corneal Topography Maps
All topographers capture corneal data that can be represented as axial curvature, tangential curvature, or refractive power maps in units of diopters. The basic elements of a corneal topography map are shown in Figure 2. Red denotes steeper curvature while blue denotes flatter curvature.
Using Corneal Topography Difference Maps to Assess Orthokeratology Lens Fits
Difference maps subtract post-wear topography data from pre-wear topography data to highlight the orthokeratology-lens-induced changes to corneal shape. (Figure 3)
Red areas indicate steepening (increased refractive power relative to the baseline pre-lens wear map), blue areas indicate flattening (reduced refractive power), and green areas indicate no change.
Difference map types for orthokeratology lens fit assessment:
- Axial difference maps enable the assessment of the regularity of the treatment zone (Figure 4A).
- Tangential difference maps allow assessment of lens centration from the treatment zone margin (red ring); a uniform red ring indicates a well-centered treatment effect (Figure 4B).
- Refractive power difference maps indicate the refractive correction achieved (Figure 4C).7
Optimal Orthokeratology Lens Fit
The ideal fit of an orthokeratology lens, called a bullseye fit, is shown in Figure 5. During overnight lens wear, an optimal orthokeratology lens fit (Figure 5A) will achieve a uniform central zone of corneal flattening on the axial difference map (Figure 5B), and a uniform ring of corneal steepening on the tangential difference map (Figure 5C).
Troubleshooting in Orthokeratology
Topography is essential for orthokeratology troubleshooting. The FitAbiliti experiential guided fitting software troubleshoots some of the common patterns (Figure 6):
- A) Central Island: The lens is too steep and tangent too tight, causing a 2.00mm area of central steepening where the apical power is steeper than the original cornea.
- B) Smiley Face: The lens is sitting too high, revealing a red “smile” pattern on the lower cornea.
- C) Frowny face: The lens is marginally tight, causing it to decenter inferiorly as seen by the red ring being decentered inferiorly.
- D) Lateral decentration: Lateral decentration shows a temporal red arc opposite to the direction of the decentration; it is decentered temporally.
- Personalized myopia management based on clinical and lifestyle factors is important.
- Orthokeratology offers both myopia management and lens-free wear in the daytime.7
- Good quality corneal topography should be part of the standard of care for orthokeratology.7
- The availability of revolutionary experiential guided fitting software such as FitAbiliti means that more practitioners may include orthokeratology as part of their myopia management portfolio.
- Up to 90%* first time fit success rate.15
- Practitioners can focus more on their patients with reduced chair time and the need for maintaining a set of trial lenses in the office.
|Dr. Monica Jong, PhD, BOptom, is Global Director of Professional Education, Myopia, Johnson and Johnson Vision; Honorary Fellow, School of Optometry and Vision Science, UNSW, Sydney, Australia. As Global Director of Professional Education, Myopia, at Johnson & Johnson Vision, she leads practitioner education initiatives around the world to support evidence-based myopia management. She was the former Executive Director of the International Myopia Institute, an organization she helped found and lead. In this role she led the development of white papers and key initiatives to bring consensus to the field of myopia management by bringing together leading researchers, clinicians, educators, policy-makers, and public health experts. Dr. Jong has published numerous peer-reviewed articles, co-created the first global online education program in myopia at the Brien Holden Vision Institute, and co-authored the WHO report on the Impact of Myopia and High Myopia. She was the former secretary of the Refractive Error Work Group of the International Agency for the Prevention of Blindness (IAPB) and contributed to position papers and advocacy initiatives in uncorrected refractive error. She has supervised a number of graduate students and speaks regularly at scientific and practitioner meetings in myopia and refractive error.|
This article is sponsored by Johnson & Johnson Vision.
† Professional Fitting and Information Guide. ACUVUE Abiliti Overnight Therapeutic Lenses for Myopia Management. Johnson & Johnson, 2023.
* Final lens fit is determined by the ECP — software is for decision support only
§ JJV Data on File 2022. ACUVUE Abiliti Overnight Therapeutic Lenses for Myopia Management-Consolidated, Approved Claims List; U.S. Only Claims
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