What is OTZ and can it improve my orthokeratology outcomes?

OTZ® (Optimized Treatment Zone) technology is changing how effective ortho k can be as a tool for myopia management. Find out how to take your ortho k fitting to the next level with OTZ. 

What is OTZ®?

OTZ is an acronym for “Optimized Treatment Zone” and refers to the unique and proprietary construction in two brands of orthokeratology lenses, BE Free and MoonLens. The OTZ is the brainchild of the KATT Design Group.  This international consortium of clinicians, researchers and industry experts was interested in developing myopia management specific lenses. The goal was to address the global need for an evolved orthokeratology technology.(1)  In addition, to design a lens that could expand the myopic and astigmatic range of a patient’s fit while also creating age specific optics for adults or children. 

During the development process, two unique lenses (BE Free and MoonLens) were devised that share OTZ technology.  Each design has its own unique reverse zone, alignment zone and peripheral system, but they share OTZ construction in the optical zone.  Precision was the first lab in the world to manufacture and test these lenses and has continued to partner with KATT throughout the development and launch of these products.

How are OTZ® lenses designed?

OTZ is both a proprietary algorithm as well as a methodology for building the modern ortho k lens.  The two principle characteristics of OTZ are:

  1. Variable optical zone diameter
  2. Patient specific shape of the posterior lens surface 

Both contribute to creating a custom tear layer shape between the lens and cornea.  The hydraulic forces of this tear layer are the main drivers of the ortho k effect so customized control over the tear layer is absolutely critical to controlling treatment effect.(2)

The variable optical zone diameter unique to OTZ lenses plays a major role in controlling the position, depth, and size of the tear layer reservoir under the lens.  Altering the diameter of the reservoir controls the resultant treatment zone and therefore the high order aberrations (HOAs) introduced to the visual system.(3,4) The ability to increase or decrease HOAs, depending on patient goals, sets OTZ technology apart from more traditional designs. 

Bigger or smaller optical zone?

Adults are, on average, more sensitive to HOAs and therefore receive calculated OTZ lenses with larger optical zones (6.0mm or greater). Whereas in the young progressing myope, higher aberrations have been shown to correlate with slower eye growth.(5,6) So using a 5.5 or 5.0 mm optical zone in these patients can increase aberrations entering the through the pupil and improve myopia management efficacy. 

Another benefit of altering the optical zone size is higher magnitudes of myopia and astigmatism can be managed.  Moving the tear reservoir closer to the corneal apex makes it easer to move epithelial tissue and therefore higher refractive targets are possible.


A MoonLens design employing OTZ technology

The ortho k lens above demonstrates the smaller optical zones, and therefore smaller treatment zone sizes, that are possible with an OTZ design.

It’s not just about optical zone size

Changing the optical zone size is only part of the OTZ story.  The second component is the shape of the optical zone.  The BE Free and MoonLens designs use an algorithm to create a specific posterior lens surface shape to control tear pressure forces between the lens and cornea.  This means OTZ technology will generate a unique tear layer for each patient based on their individual eye shape, Rx and age.

The KATT group hypothesized that customization of the optical zone size and posterior lens surface to control over tear layer size, position, shape, and depth could improve outcomes, specifically when it comes to myopia management. Evidence supporting this hypothesis was published this year. In a 2021 study, BE Free lenses using 5.0 mm OZ OTZ technology were fit on a group of subjects and compared to a group of subjects that were fit with 6.0 mm OZ BE Free lenses.(7) After 12 months of wear, the average progression of axial length in the 5.0 mm group was 0.04 mm and 0.17 mm in the 6.0 mm group. For reference, the average progression over a 12 month period for a study group wearing traditional single vision glasses with the same age range and with similar ethnic backgrounds was 0.37 mm.(8)

Next generation ortho k

Based on the study results we’ve seen so far, it appears that OTZ technology improves upon the efficacy of traditional ortho k. The ability to customize all aspects of the tear layer under the lens by changing the optical zone size and altering posterior lens shape moves OTZ designs beyond conventional, first generation designs into a new era of ortho k.

So if you want to take your ortho k fitting to the next level, consider using a lens like BE Free or MoonLens that employs OTZ. To find out more about how OTZ lenses work or other information about ortho k lenses, send us a note via our contact page or send an email to consultation@ptsoptics.com


1. Holden BA, Fricke TR, Wilson DA, Jong M, Naidoo KS, Sankaridurg P, Wong TY, Naduvilath TJ, Resnikoff S. Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050. Ophthalmology. 2016 May;123(5):1036-42. doi: 10.1016/j.ophtha.2016.01.006. Epub 2016 Feb 11. PMID: 26875007.

2. Mountford J, Ruston D, Dave T, Orthokeratology: Principles and Practice, Butterworth-Heinemann, 2004, P: 269-284.

3. Kojima R, Turpin S, Caroline P, Kinoshita B, Lampa M, Andre M, Orthokeratology Treatment Zone Size and its Relationship to High Order Aberrations, Poster, GSLS, 2018, Las Vegas, NV.

4. Invergo A, Fujimoto M, Kojima R, Caroline P, Lampa M, Andre M, Kinoshita B, Poster, GSLS, 2021, Las Vegas, NV.

5.  Lau JK, Vincent SJ, Cheung SW, Cho P. Higher-Order Aberrations and Axial Elongation in Myopic Children Treated With Orthokeratology. Invest Ophthalmol Vis Sci. 2020 Feb 7;61(2):22. doi: 10.1167/iovs.61.2.22. PMID: 32068792; PMCID: PMC7326571.

6  Lau JK, Vincent SJ, Collins MJ, Cheung SW, Cho P. Ocular higher-order aberrations and axial eye growth in young Hong Kong children. Sci Rep. 2018 Apr 30;8(1):6726. doi: 10.1038/s41598-018-24906-x. PMID: 29712928; PMCID: PMC5928153.

7. Guo B, Cheung SW, Kojima R, Cho P. One-year results of the Variation of Orthokeratology Lens Treatment Zone (VOLTZ) Study: a prospective randomised clinical trial. Ophthalmic Physiol Opt. 2021 Jul;41(4):702-714. doi: 10.1111/opo.12834. Epub 2021 May 15. PMID: 33991112; PMCID: PMC8251614.

8. 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. PMID: 22969068.