|Quarterly newsletter on Soft Specialty Contact Lens |
Research, Developments, Designs and Materials WINTER 2012
|WORLD WIDE VISION
Custom Silicone Hydrogel Contact Lenses for High Astigmatism
Patients needing either a high amount of astigmatic correction or an astigmatic correction combined with a high spherical component that falls outside of the range allowed by standard, off-the-shelf designs have always been a big challenge. Three cases of patients will be presented here, seen in a university optometry clinic, who were refit out of their hydrogel contact lenses into silicone hydrogel custom contact lenses for astigmatism. One case is about a 27-year-old female with a S-16.75 - 6.00 x 177 refraction who experienced significant neovascularization. A second involved a 26-year-old female graduate student with a prescription of OD: S+3.75 -6.00 x 170 and OS: S+3.00 -4.00 x 003 with fluctuating vision, mild corneal deformation, and also showing signs of neovascularization. In a third case, a 20-year-old college student with a non-standard prescription of S+7.50 -4.00 x 005 was fitted with a custom soft lens to allow for extra oxygen transmission, which reduced the risks of hypoxia related complications. The ability to provide soft contact lenses in high astigmatic powers that provide increased oxygen compared to previous hydrogel lenses is a significant benefit. Click here for full report.
Pence, OD, FAAO
Associate Dean, Clinical and Patient Care Services
Indiana University School of Optometry
Bloomington, Indiana (USA)
|IN THE NEWS|
Piggy Back Power
Effective Power of a Soft Lens underneath a RGP Lens
The effective power of a soft lens under an RGP lens has been known to be less than the true lens power, but by how much? Minhee Woo and Barry Weissman, who both graduated from the University of California, Berkeley School of Optometry (USA), in an interesting article in Contact Lens Spectrum (November), search for the answer. The power effectiveness depends on whether it is a hyperopic or a myopic prescription and is also dependent on the base curve of the lens. The effective lens power (not taking lens power into account) is estimated in percentage of the original power of the soft lens and ranges from 14 percent to 28 percent in lenses of -3D to +3D in original power. For the full table with power range and explanation of the effect, see the link in this item
|IN THE LITERATURE|
Silicone Hydrogel Toric Lenses
Material Availability & Extended Parameter Range
If any soft lens design can benefit from an increase in oxygen permeability, it must be toric lenses - because of the increased thickness required to stabilize them. Tiffany Andrzejewski and Neil Pence, in an article in the September issue of Contact Lens Spectrum, focus on this. They not only list all currently available toric silicone hydrogel lenses and their parameters, they also look at current custom toric silicone hydrogel lens options. Their parameter range extends all the way from sphere powers of +30D to -30D and cylinder powers up to -12D, in 1 degree steps.
|IN THE LITERATURE|
Replacing Discontinued Soft Lenses
In Search of a Life Saver
It used to be challenging to find a good alternative for a soft lens that was discontinued by the manufacturer, especially if the specific lens was available as a silicone hydrogel lens, but that is no longer the case. Several companies now offer custom made soft lenses for that purpose. Some of them aim specifically at mimicking the original, now discontinued lens. For some patients - and practitioners - this can be a 'life saver.' See the link below for the full column on Contact Lens Design & Materials by Neil Pence.
|ON THE WEB|
IACLE Contact Lens Course
Complete Soft Contact Lens Fitting Module Online in PowerPoint Format
IACLE (International Association for Contact Lens Educators) is in the process of making all of its ten contact lens fitting modules available on the organization's website. The first five modules as PowerPoint presentations are now free to download for anyone interested (after registration), with information on contact lens fitting and care, slit lamp techniques, etc. This includes a substantial section on soft lens fitting approached from a neutral, objective, global angle. Future available modules will include specialty lens topics.
IACLE Contact Lens Course
|CLINICAL REPORT I
Bandage Silicone Hydrogel Lens
In Combination with Autoglobus Serum Eye Drops
Persistent epithelial defects develop when the epithelium fails to regrow over a defect within the expected time. These are difficult to treat and can result in significant ocular surface morbidity and visual loss. This study by Jin Choi and So-hyang Chung in Eye & Contact Lens of November 2011 on eight eyes in eight patients demonstrates that the combination of a silicone hydrogel lens and serum eye drops may effectively treat intractable persistent epithelial defects.
|CLINICAL REPORT II
Reverse Geometry Soft Contact Lens
Despite the advances in corneal surgical techniques, a significant percentage of postoperative patients still will require contact lenses to optimize their visual outcome. Greg DeNaeyer in Contact Lens Spectrum looks at the options available for these patients - from RGP to hybrid and from scleral to specialty soft lenses. A specialty soft lens with an increased center thickness may adequately return patients to their best potential visual acuity if the irregularity is not too severe, DeNaeyer reports. He describes a case of a reverse geometry soft contact lens on a patient post-penetrating keratoplasty after having complications with a PRK treatment prior to that. The best corrected visual acuity with a refraction of S+3.00 -4.75 x 116 was 20/30. The reverse geometry soft lens fits perfectly and provides the patient with 20/25 vision.
Optic Zone Selection for
Custom Soft Contact Lenses
Matt Lampa & Mark André
Optic zones in molded (non-custom) soft contact lenses generally have a set diameter that ranges between 7.5mm - 9.0mm. Generally, the relationship between optic zone diameter and the power of the contact lens is an inverse one: as the dioptric power of the contact lens increases, the overall diameter of the optic zone decreases. This is generally done in an attempt to control the contact lens thickness. The visual aberrations resulting from a smaller optic zone can be particularly troublesome for high ametropes. We have found that increasing the diameter of the optic zone, in some cases several millimeters beyond the standard size, has improved subjective visual outcomes with custom soft contact lenses while maintaining the same overall effective power. Click here for the full report.
This Newletter is Kindly