Investigation of the Effect of Short-term Orthokeratology With Increased Compression Factor on Ocular Parameters


Orthokeratology (ortho-k) is a clinical technique that uses reverse geometry rigid gas permeable contact lens exerting positive pressure on the central cornea to temporary reduce refractive error. Researchers have shown that this treatment is effective for myopia control in low to high myopes, with and without astigmatism. Most designs of ortho-k lenses in the market are fitted based on the Jessen formula. The compression factor was introduced to compensate for the regression of the ortho-k effect during the no lens-wear period, so that the wearer can obtain clear distance vision throughout the day and most lens designs use a compression factor of 0.50-0.75 D. However, in a retrospective study (mixed brands of ortho-k lenses), it showed that most patients did not achieve an over-correction of 0.75 D. In order to achieve an over-correction of 0.75 D, an extra flattening power of about 1.50 D instead of 0.75 D should be be targeted. The increased compression factor is expected to increase the target reduction and it may play a role in myopic control and providing a higher successful rate in fitting ortho-k lenses.

Study Type

  • Study Type: Interventional
  • Study Design
    • Allocation: Randomized
    • Intervention Model: Single Group Assignment
    • Primary Purpose: Treatment
    • Masking: Double (Participant, Outcomes Assessor)
  • Study Primary Completion Date: November 18, 2016

Detailed Description

Subjects were fitted with ortho-k lenses of conventional (0.75 D) and increased (1.75 D) compression factor. The laterality of the compression factor for each subject was randomised. Subjects were instructed and trained with proper lens handling and disinfection procedures. Lenses were given to the subjects only when they demonstrated proper techniques. All subjects were required to attend regular follow-ups (baseline, first overnight, and weekly over one-month period). The follow-ups were scheduled (except for the first overnight which was scheduled in the early morning) at a similar time to the baseline visit (+/- 2 hours) to minimise any potential influence of diurnal variation on ocular biometrics. Additional unscheduled visits were provided when necessary to ensure good ocular health and vision throughout the study period.


  • Device: Orthokeratology
    • It is a kind of rigid permeable lens.

Arms, Groups and Cohorts

  • Sham Comparator: Ortho-k lens with normal compression factor
    • The eye wears ortho-k lens with normal compression factor to achieve plano (+/- 0.25D) correction.
  • Active Comparator: Ortho-k lenses with increased compression factor
    • The eye wears ortho-k lenses with increased compression factor to achieve 1 diopter (+/- 0.25D) over correction.

Clinical Trial Outcome Measures

Primary Measures

  • Changes in Spherical Equivalent Refraction
    • Time Frame: baseline and one month
    • Maximum plus for maximum visual acuity was used as the criterion for subjective refraction. Spherical equivalent refraction was calculated by adding the sum of the sphere power with half of the cylinder power.

Secondary Measures

  • Changes in Subfoveal Choroidal Thickness
    • Time Frame: baseline and one month
    • The subfoveal choroidal thickness was determined as the thickness between the outer retinal pigment epithelium/Bruch’s membrane complex and the inner chorioscleral interface.
  • Changes in Higher Order Aberrations
    • Time Frame: baseline and one month
    • Ocular higher order aberrations were measured using Shack-Hartmann aberrometer. The wavefront data was fitted with a sixth order Zernike polynomial over a 5-mm pupil size.

Participating in This Clinical Trial

Inclusion Criteria

1. 6 to 10 years old 2. Myopia: between 0.50 D and 4.00 D in both eyes 3. Astigmatism: <1.50 D; ≤ 1.25 D for with-the-rule astigmatism (axes 180 ± 30); ≤ 0.50 D for astigmatism of other axes in both eyes 4. Anisometropia: ≤ 1.50 D 5. Symmetrical corneal topography with corneal toricity <2.00 D in both eyes 6. Agree for randomization Exclusion Criteria:

1. Contraindications for orthokeratology wear (e.g. limbus-to-limbus corneal cylinder and dislocated corneal apex) 2. Any type of strabismus or amblyopia 3. Myopic treatment (e.g. refractive surgery and progressive lens wear for myopic control) before and during the study period 4. Rigid contact lenses (including orthokeratology lenses) experience 5. Systemic condition which might affect refractive development (for example, Down syndrome, Marfan's syndrome) 6. Ocular conditions which might affect the refractive error (for example, cataract, ptosis) 7. Poor compliance for lens wear or follow-up

Gender Eligibility: All

Minimum Age: 6 Years

Maximum Age: 10 Years

Are Healthy Volunteers Accepted: Accepts Healthy Volunteers

Investigator Details

  • Lead Sponsor
    • The Hong Kong Polytechnic University
  • Collaborator
    • Menicon Co., Ltd.
  • Provider of Information About this Clinical Study
    • Principal Investigator: Pauline Cho, Professor – The Hong Kong Polytechnic University
  • Overall Official(s)
    • Pauline Cho, PhD, Principal Investigator, The Hong Kong Polytechnic University


Cho P, Cheung SW, Edwards M. The longitudinal orthokeratology research in children (LORIC) in Hong Kong: a pilot study on refractive changes and myopic control. Curr Eye Res. 2005 Jan;30(1):71-80.

Cho P, Cheung SW. Retardation of myopia in Orthokeratology (ROMIO) study: a 2-year randomized clinical trial. Invest Ophthalmol Vis Sci. 2012 Oct 11;53(11):7077-85. doi: 10.1167/iovs.12-10565.

Chen C, Cheung SW, Cho P. Myopia control using toric orthokeratology (TO-SEE study). Invest Ophthalmol Vis Sci. 2013 Oct 3;54(10):6510-7. doi: 10.1167/iovs.13-12527.

Chan B, Cho P, Mountford J. The validity of the Jessen formula in overnight orthokeratology: a retrospective study. Ophthalmic Physiol Opt. 2008 May;28(3):265-8. doi: 10.1111/j.1475-1313.2008.00545.x.

Citations Reporting on Results

Wan K, Lau JK, Cheung SW, Cho P. Refractive and corneal responses of young myopic children to short-term orthokeratology treatment with different compression factors. Cont Lens Anterior Eye. 2020 Feb;43(1):65-72. doi: 10.1016/j.clae.2019.10.134. Epub 2019 Nov 6.

Lau JK, Vincent SJ, Cheung SW, Cho P. The influence of orthokeratology compression factor on ocular higher-order aberrations. Clin Exp Optom. 2020 Jan;103(1):123-128. doi: 10.1111/cxo.12933. Epub 2019 Jul 1.

Lau JK, Wan K, Cheung SW, Vincent SJ, Cho P. Weekly Changes in Axial Length and Choroidal Thickness in Children During and Following Orthokeratology Treatment With Different Compression Factors. Transl Vis Sci Technol. 2019 Jul 23;8(4):9. doi: 10.1167/tvst.8.4.9. eCollection 2019 Jul.

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