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Advertorial

Breathing new life into toric lenses

How design influences oxygen transmissibility

19 May 2017 by Advertorial

Over the last few years, there has been a shift towards daily disposable contact lens prescribing and with the comfort, vision quality and convenience of this modality, it is clear that this trend is set to continue.

As the popularity of daily disposable lenses continues to grow, and with the prevalence of clinically significant astigmatism indicating that a third of all contact lens wearers should be fitted with a toric design,1 eye care professionals should be encouraged to consider the oxygen performance of  toric daily disposable lenses as a whole to avoid chronic hypoxia. 

Toric lens stability and orientation, regardless of modality or product, is managed by incorporating eyelid stabilisation features to the lens design; all of which employ regional changes in thickness (and a corresponding reduction in Dk/t). However, the conventional approach that contact lens manufacturers use to publish oxygen transmissibility is the measure of a single value of Dk/t at the geometric centre of a -3.00 lens.

Figure 1

Thickness differences are of course, not limited to lens design; they vary widely between the parameter ranges of a particular product. For example, the centre thickness of a +4.00 lens in a toric design will be quite different to a -4.00 lens in a toric design in the same material. It is therefore important to be aware that conventional reporting of Dk/t is not a completely reliable measure for predicting oxygen transmissibility for either parameter range or lens design.

Up to now, eye care professionals have had limited choice in daily disposable toric lens material.  More options that are able to support optimum ocular physiology would be a valuable addition to the current portfolio of daily disposable toric lenses. 

New MyDay toric from CooperVision, has the potential to address the challenge of providing stable, reliable vision and comfort while at the same time addressing any concerns around hypoxia for astigmatic contact lens wearers keen to opt for a daily disposable lenses. Oxygen profiles of this lens give a clear indication of its oxygen transmissibility compared to hydrogel lenses.

Figure2

Given that regional variations in thickness are essential characteristics for eyelid stabilisation of modern soft toric contact lenses, choice of contact lens materials with oxygen transmissibility levels that help to maintain corneal physiology should be a key consideration for both new and existing astigmatic contact lens wearers. 
 

Find out more on the CooperVision website or contact your CooperVision business development manager.

References

  1. Young G, Sulley A, and Hunt C. Prevalence of astigmatism in relation to soft contact lens fitting. Eye Contact Lens 2011; 37:20-25
  2. Based on manufacturer’s published Dk (FATT) and t values, Association of Contact Lens Manufacturers, 2016
  3. PhaseFocus Dk/t lens profile report, April, 2016. Standardised scale to allow for like-for like comparison across entire lens area. ACUVUE is a trademark of Johnson and Johnson Medical Limited. DAILIES and AquaComfort PLUS are trademarks of Novartis AG
  4. Holden BA, Mertz GW. Critical oxygen levels to avoid corneal edema for daily and extended wear contact lenses. Invest Ophthalmol Vis Sci. 1984; 25(10): 1161-1167.