Quarterly newsletter on Soft Specialty Contact Lens
Research, Developments, Designs and Materials   SPRING 2013

Sagittal Height Calculator

Based on Peripheral Corneal Angle Measurement

Whereas corneal central radius of curvature, corneal eccentricity and even diameter have proven to be poor indicators of overall sagittal height of the eye as covered in part I and part II of this series, one indicator may prove to be a better predictor: the peripheral corneal angle. In this last part of the trilogy on soft lens fitting and ocular surface shape, a calculator is introduced that, in a step-by-step manner, can help better predict overall sagittal height and can therefore be used in soft lens fitting. The calculator combines the sagittal height of the cornea over a chord of 10.0 mm as measured by corneal topography; the corneal peripheral corneal angle, also measured by corneal topography; and a scleral angle compensation factor. If the chord diameter of the desired soft lens that is going to be fitted is known, the calculator will provide the best sagittal height estimation possible for an optimal soft lens fit. Click here for full report. 


Patrick Caroline and Randy Kojima
Portland (OR) USA
Expanding Options for Irregular Corneas 
Customized Soft Lenses, Visual Acuity, Comfort, Quality of Life


Craig Norman, Renee Reeder, Robert Ryan and Stephanie Su discuss expanding the lens options we have for the irregular cornea, by looking at the feasibility of using a customized soft lens that delivers visual acuity and comfort. The lens that is discussed primarily, the Kerasoft IC, is looked at from the perspective of patient selection, the fitting process, lens care and handling techniques, refitting procedures from RGP lenses and quality of life issues. See the special supplement issue of Contact Lens Spectrum (November 2013). Photo: Form Fruste Keratoconus Elevation Map - Eye Surface Profiler
The Impact of Eyelid and Eye Contour on Toric Soft Contact Lens Behaviour
Toric Soft Lenses, Eyelid Shape, Palpebral Aperture, HVID

Investigators used high-speed digital cameras to evaluate eyelid and eye contour factors that can influence the fitting of toric soft contact lenses in Chinese eyes. Four pairs of significant correlations were found: (1) larger palpebral aperture was associated with a greater possibility of nasal rotation of the corresponding lens; (2) the larger the central lower lid angle, the worse the rotational stability; (3) the smaller the lower lid angle of the medial canthus, the more quickly the lens temporal rotational recovery; and (4) the larger the horizontal visible iris diameter (HVID), the looser the lens fitting. Finally, when assessing correlations between some lens parameters and the orientation of the lens, they found that lower sphere values were associated with quicker lens recovery.  

Is Wavefront Aberrometry a Good Fit for Contact Lens Practice?
Soft Lens Carrier, Piggyback, Contact Lens Optics


Just as wavefront aberrometry data can improve refractive surgery outcomes, it may be possible to apply this technology to contact lens fitting principles to bring contact lens visual acuity as close as possible to the best spectacle corrected visual acuity, according to the author of this article. Higher-order aberration data from normal eyes reveals that the two most prevalent aberrations are vertical coma and spherical aberration. These and the less prevalent aberrations can be corrected with contact lenses, but deformation-induced aberration is one variable that will lead to challenges in advanced wavefront-guided contact lenses, the article states. This particular complication presents itself in the same manner as the variability in the biomechanical aspects of the healing limits of wavefront-guided refractive surgery. New design strategies to develop non-deforming soft lenses will help to advance wavefront-guided contact lenses by reducing the noise from these deformation-induced aberrations, the article states.

The Efficacy and Safety of a Fenestrated and Channeled Soft Contact Lens
Oxygen Permeability, Tear Mixing, Corneal Edema, Dk/t

An article in Contact Lens & Anterior Eye reports the efficacy and safety of a fenestrated and channeled soft contact lens compared to a standard and non-fenestrated soft contact lens in experienced soft contact lens wearers. Central corneal swelling was 1.921.73% in the fenestrated/channeled lens vs. 5.262.14% in the standard lens. There was no significant difference between the groups in terms of visual acuity or adverse events. The authors conclude that the use of fenestrated/channeled lenses can lead to reduced corneal swelling and that the newly incorporated features appear to improve tear mixing and, thereby, the oxygen supply to the cornea.


'Soft Focus Las Vegas

Lens Design, Aberrations, Hypoxia, Myopia Control, Irregular Cornea  


As reported in the last SoftSpecialEdition newsletter the renewed interest in specialty soft contact lenses was one of the main topics at the annual Global Specialty Lens Symposium in Las Vegas. In addition to several lectures from the podium, the poster session also hosted a number of entries looking at customized soft lens fitting, such as soft lenses for myopia control (Bickle), the effect of thickness and material on corneal swelling (Caroline), performance of soft lenses and higher-order aberrations (Gauthier), soft lens case reports on corneal ectasia (Dávila-Garcí) the visual rehabilitation after penetrating keratoplasty with a reverse geometry soft lens (Harthan), tear volume, osmolarity and optical quality in silicone hydrogel contact lens wearers (Montani), variation in oxygen transmissibility within the optic zone of modern silicone hydrogel soft toric contact lenses (Hough) and more - all available as PDF files from the meetings website. 


Custom Soft Lens Applications

Stephanie Woo


The GPLI in February hosted an interesting webinar on custom soft lens applications. Stephanie Woo presented the webinar, which can be downloaded from the GPLI.info website, that looks at larger and smaller lens diameters, wider range of curvatures, wider range of sphere and cylindrical powers, exact cylinder axis and custom lens thickness. It addresses the discontinuation of several parameters by large contact lens manufacturers, and the void this has created for some of our lens patients. 

In this Edition:
Sagittal Height
Irregular Corneas
Eye Contour & Toric Soft Contact Lens Behaviour
Wavefront Aberrometry
Fenestrated and Channeled Soft Contact Lenses
Soft Focus (on) Las Vegas

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