Associate Dean, Clinical and Patient Care Services
Indiana University School of Optometry
Bloomington, Indiana (USA) 

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

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. 

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.

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 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.