Prescribing Higher Powers in a Silicone Hydrogel Lens

Stuart A. Gindoff, OD, MBA, FAAO

Skip Gindoff received Bachelor degrees in zoology (Rockford College, Illinois) and visual science (Illinois College of Optometry) before earning his Doctor of Optometry degree (ICO) and an MBA from the University of Sarasota. He has taught foreign medical graduates clinical procedures in ophthalmology at the Little Company of Mary Hospital in Chicago and served 2 years as Chief of the US Air Force Hospital Eye Clinic at Seymour Johnson Air Force Base in North Carolina. Currently he is clinical assistant professor of ophthalmology at the University of South Florida, College of Medicine and an adjunct clinical associate professor at Nova Southeastern University College of Optometry.
A national lecturer and consultant to the ophthalmic industry, Stuart Gindoff currently provides continuing education for ophthalmologists and optometric physicians and practices in one of the largest ophthalmological/optometric practices in Florida, Center For Sight.

To those of us who feel that a silicone hydrogel lens is the safest of contact lens modalities, frustration arises when patients’ refractive errors exceed that of the lenses commercially available (see Table 1).  Although as of this writing, approximately 94% (CIBA Vision data) of the refractive error population can be treated with lenses ranging from -10.00 to +6.00D, the question arises - What do we do with the smaller group of patients whose refractive error requirements exceed the available products?  Do we prescribe a lesser quality or older technology lens?

Table 1

* Reprinted from www.siliconehydrogels.org, Dec 2005 Feature review

We’ve all been confronted with this issue.  Let’s use an easy example.  Your data indicated that your patient should be fit with a -3.00 / -1.00 X 180 powered lens but for a long time, that particular power just wasn’t available in a silicone hydrogel.  Did we tell the patient, “sorry, I don’t have a lens for you,” or did we work at finding an acceptable sphere (using an astigmatic masking technique) or, when the Acuvue Advance for Astigmatism was released, did we try a -3.00 / -0.75 X 180?

Contact lens power requirements are, in many cases, different from what one would prescribe in spectacles yet we all have satisfied many of our patients’ requirements by using innovative and imaginative techniques.  This paper describes a relatively easy and safe piggyback design to deal with the very high powers that might be required for a patient whose requirements exceed the silicone hydrogel lenses that are commercially available.  The overall strategy is to always begin with the steepest base curve available in the silicone hydrogel lens of choice. The author has employed this technique on at least twenty patients of various ages, the youngest being an 8 year old boy with significant hyperopia associated with accommodative esotropia, and the oldest, an 86 year old man with scarred corneas from trachoma. The following case study highlights the success that can be achieved with this silicone hydrogel piggy-back system in an 8 year old boy with very high myopia.

Case Study

Eight year old JB had been myopic since first professionally evaluated at age 2. 
At presentation his K’s were OD 46.50 / 47.00 X 180 and OS 46.00 / 46.75 X 180.  Manifest and cycloplegic refractions showed OD -16.00 / -0.50 X 180 (20/40) and OS -14.50 / Sph (20/40).  There were no overt reasons not to fit this child with silicone hydrogel lenses.

Irrespective of lens choice, we always begin by choosing the steepest base curve that will approximate the patient’s corneal curves. First, we view the power requirement at the corneal plane to initially choose the brand of lens to be fit.  The corrected vertex power for JB at 12 mm was OD -13.60D and OS -12.35D, each power clearly higher than provided in your diagnostic lens set for any brand. 

For the right eye we had the choice of either a -13.50D or -13.75D endpoint. To achieve the -13.50D endpoint, we inserted an 8.4 mm Focus Night & Day -10.00D lens as the “ocular lens.”  Next, we inserted a -3.50D, 8.4 mm lens directly on top of the ocular lens as the “objective lens”.  

For the left eye we again first inserted a -10.00D, 8.4 mm ocular lens followed by a -2.25D, 8.4 mm silicone hydrogel. 

Monocularly, JB achieved 20/30+ within minutes and was 20/25 binocularly.  Manifest overrefraction was +0.25 – 0.50 x 180 in each eye.

JB was put on a Complete Moisture Plus care regimen.  He was instructed to rub each lens with solution prior to placing the lens in the appropriate case.  If possible, he was instructed to remove the “objective” lens first, right eye then left eye, followed by the “ocular” lens, right eye then left eye.  Initially JB was told to wear his lenses all his waking hours and to remove them before going to bed.  After the first month checkup, his corneas were completely normal and he was permitted to begin extended wear with this piggyback system.  He was re-evaluated a week after beginning extended wear and then three weeks later before being put into the typical, six month recall system.

Currently JB is 11 years old and is still successfully wearing the same extended wear silicone hydrogel piggyback system, with minor changes to lens power.

 
Recommendations

As it is cumbersome for patients to place both lenses (handling issues as well as the inability to see very well) on their fingers and then insert the pair together, we recommend to insert the ocular lens first (higher power lens), followed by the objective lens on top.

Do not try to split the lens powers relatively evenly over the ocular and objective lenses as the lenses will typically de-center from each other and visual acuity and comfort will be compromised.  There is a definite relationship between lens curvature and its power, and therefore you want the highest power with the steepest curve on the corneal tear film.

From a practice management perspective, provide two lens care cases of varied color that are identified as #1 and #2 with a Magic Marker, along with the disinfection system appropriate for your lens.  We typically provide AMO Complete Moisture Plus solution and in children with allergies, I use Clear Care.

When removing piggyback lenses, it is common for each lens to come out independently. Therefore the first lenses removed are the objective lenses which are placed into lens case #2; then the ocular lenses are removed are placed into lens case #1.  If both lenses should happen to be removed on the first go, the patient is taught how to separate them and keep track of which lens is which.  Switching the lenses, i.e., the objective lens inserted first followed by the ocular lens does permit fair visual acuity but there usually is a sensation caused by the lens akin to having a lens on inside out.

In my experience, rubbing each lens is vital even though the manufacturers market contact lens solutions as “no rub.”  Silicone hydrogels will sometimes collect lipid so soaking alone will not adequately remove these surface deposits. Alcohol based cleaners usually work well at removing lipids.

It is not uncommon to have patients see very well and sleep for weeks in piggyback lenses.  Obviously, practitioners must maintain careful and routine follow-up.  Patients with significant myopia realize that they are “special” and understand that their case is more demanding and more costly.  However, at the end of the day, they are some of your best referral sources!