In most cases, the advantages of silicone hydrogel lenses compared to previous soft lenses include lower risk of corneal edema and neo-vascularization, and lower incidence of complications with extended wear use (overnight wear).
Although the incompatibility of contact lens polymers and MPS's, Specular Microscopy, and MPS sensitivites could be separate articles, we have left it as one for now.
We have included new information to this article that explains why we do Specular Microscopy. All eye doctors now fit SH Lenses because we need to maintain the integrity the corneal endothelium. Excess edema of the corneal stroma disrupts the uniform and periodic spacing of collagen fibrils, creating light scatter 1. This may be the reason you may not see clearly through your eyeglasses if you wear contact lenses and is the reason why we ask you to not sleep in your lenses before a refraction for an eyeglass prescription. Persistent corneal edema secondary to using lower DK lens can affect corneal endothelium health. Specular Microscopy allows us to determine the health of your corneal endothelium. Note, that references to Specular Microscopy in this article are limited to contact lenses and persistent edema from using lower DK lenses, and is not intended to discuss endothelial dystrophies, such as Fuch's dystrophy.
Refitting Considerations and What to Expect
When using regular soft lenses the cornea is prone to swell (edema) which induces an artificially higher myopic (nearsighted) correction upon testing. When being refit from regular disposables to SH lenses, it's possible that as the corneal edema disappears after a few weeks, your contact lens power might change and be lower than on the day of your exam. The benefit is that your eyes have become more healthy, but the prescription may need to be changed. Therefore, when changing to SH lenses, follow-up care with your doctor is important. You'll know if your power reduces because it will be more difficult to focus when reading, especially if you're over 40-45 years of age.
Also, in some patients, the silicone material tends to attract more lipid deposits and mucin, which may cause blurred vision, discomfort, and shorter lens life. There are some cases where a patient is not able to adapt well to the silicone material. We will try different brands to find one that is acceptable. However, the health advantages and increased comfort that most wearers experience exceed the occurrences of adverse reactions in those who do not adapt well to the material.
Some patients tell us that SH lenses feel dryer than HEMA lenses. Silicone is not as hydrophilic (wettable) as the regular soft lens materials, so some manufacturers treat the lenses to make them more wettable. Ciba puts a plasma coating on their lenses and Acuvue uses Hydraclear to make the lenses more wettable. However, it is not uncommon for patients to report more dryness and shorter lens life than regular HEMA lenses, and it's possible you may prefer the older generation disposable lens materials for those reasons. We have aslo seen allergies/sensitivities to the wetting agents used by the manufacturers.
Allergies and/or Sensitivities to Wetting Agents Used in Silicone Hydrogel Lenses
Although not common, we have seen patients who are allergic to the wetting agents used by some manufacturers. Symptoms and signs are irritation, itching, burning and infiltrative keratitis. Symptoms resolve when lenses are not used, then resume when lenses are used. When that happens we try various brands until we find one that is acceptable.
Clarity of Vision With Different Polymers
Although not limited to SH lenses the clarity of vision can vary with the plastic used by the manufacturer. If you do not see clearly and the prescription is accurate we will try another brand. We have found Alcon/Ciba Air Optix Aqua and Night & Day, Coopervision Biofinity, Acuvue Oasys and BL Purevision contact lenses to have excellent clarity.
Multipurpose Disinfecting Solution (MPS) Issues - Sensitivities/Allergies/Toxicity
We see patients who have been fit with a silicone hydrogel lens and complain of discomfort or irritation. Many times it's due due to an incompatibility between the silicone material and the disinfection solution, which seems to be particular to each patient. The patient changed their contact lens plastic, but not their solution, and now have a problem with incompatibility. Please note, MPS sensitivities are not limited to SH polymers and are one of the more common complications associated with all types of contact lenses, and have been for years. You have to find the right combination of contact lens poymer, MPS, and patient sensitivity.
A study by Dr. Gary Andrasko2
has shown that some lens disinfecting solutions have a higher degree of bio-incompatibility with various polymers A bio-incompatibility may cause irritation, corneal staining or infiltrative keratitis, (see Clinical Photos
) and other solutions may be better.
Alcon Clear Care
, and AO Sept Plus
which are hydrogen peroxide based, have proven to be the best disinfecting products for SH and HEMA lenses because we see less allergic sensitivities Another multi-purpose solution (MPS), Opti-Free Pure Moist
seldom causes problems, and is also a recommended solution for SH lenses. However, and interestingly, we see patients using an SH lens and using a non-recommended solution, and they have no problems. Therefore, the occurrence of problems seems to vary with the patient, the solution, and the contact lens polymer.
Dr. Andrasko has been doing an on-going study of incompatibility of various disinfecting soluitons and contact lens polymers for several years. Doctors refer to it as the "Andrasko Corneal Staining Grid" and can be viewed at http://staininggrid.com/
Because bio-incompatibility between an MPS and polymer is a possible reason for patient dissatisfaction with their contact lenses; we ask you to understand that idea if you have a problem and report it to your doctor.
Based upon Dr. Andrasko's study Clear Care is one of the the best disinfecting systems. However, Alcon's Opti-Free Pure Moist, Opti-Free Express, and Opti-Free Replenish have been shown to cause minimal problems. I have been prescribing Pure Moist for several months and have not seen a problem. Dr Andrasko's study shows Pure Moist to be slightly superior to the other Optifree products, by a fraction of 1-2%. Another new MPS is Bausch & Lomb Biotrue
, and according to Dr. Andrasko, has a higher degree of incompatibility with some polymers. However, I have patients using Biotrue and they prefer it over other MPS's. You have to find the right combination of polymer, MPS, and patient sensitivity.
Disinfecting Recommendations - Finding the Right Combination
Our first recommendation would be to find an MPS which is compatible with the patient and polymer. This would provide the convenience of a single solution MPS. This would also eliminate the possibility of the patient accidentally using Clear Care or AO Sept as a rewetting agent, causing a red eye.
Our second recommendation for disinfection of SH lenses (and probably all lenses) is Clear Care or AO Sept because they're hydrogen peroxide based and are less likely to cause corneal irritation with most polymers. As anecdotal evidence, I have many patients who have switched to Clear Care and continue with it because they subjectively report that it keeps their lenses cleaner.
However, please read the instructions carefully; Clear Care and AO Sept cannot be used as a rewetting solution or placed in your eye, as many MPS's can. Clear Care also requires more patient instruction and is not as convenient as an MPS. AO Sept was the precursor to Clear Care and was commonly prescribed to reduce incidence of toxicity and has successfully been used since 1983.
Karen, who is one of my patients, told me that she can use AO Sept, but not Clear Care. Karen did the research on the following idea. Clear Care contains a cleansing agent, Pluronic 17R4 which AO Sept does not. That again presents subjective information that alterations in formulations can affect a small population group, and why you have to find the right combination for each patient.
A third recommendation for all patients when changing to a different brand of contact lens (and therefore polymer) is to be aware of the possibility of a sensitivity reaction/incompatibility and the symptoms, and report it to your Doctor. The Doctor and patient will eventually find a compatible SH lens polymer and MPS. I've been working with Christine for many months in finding the right combination. We believe she was allergic to the wetting agent used by the manufacturer because her chief complaint was itching, which is the hallmark complaint of allergy.
Diagnosis of MPS Sensitivities/Allergies/Toxicity
Your contact lenses are not as comfortable as they were 3 or 4 months ago. Symptoms include low grade irritation and redness which has been slowly increasing. Vision with glasses is not clear because of the staining and infiltrates (assuming your eyeglass Rx is up to date and accurate). If you have been successfully using contacts and begin to have decreasing comfort or irritation and increasing redness, ask yourself if you have changed solutions in the past 1-3 months. My experience has been that the irritation slowly builds over that time frame and then comes to the point where the patient eventually consults us. Severe pain is not a symptom of low grade MPS toxicity unless you have let it progress to a corneal ulcer. Severe pain could be an abrasion, corneal ulcer, foreign body, or even acute glaucoma which all require emergency in-office treatment.
Treatment of MPS Sensitivities/Allergies/Toxicity
Any corneal staining or infiltrates resolve over the same time frame as they arose. We would ask the patient to discontinue contact lens usage until the cornea is clear. We may prescribe a mild antibiotic/steroid or mild steroid drop, depending on severity, to hasten recovery, and protect from development of a corneal ulcer if the epithelium is damaged. After the cornea is clear we would resume contact lens usage with Clear Care and monitor.
If you have been fit with a silicone hydrogel lens and do not like them, please communicate that to your Optometrist. You will be refitted to another silicone hydrogel lens, to see if another brand or plastic is better, or be refitted to your previous brand or non- silicone hydrogel lens material, whichever you prefer.
The Future of Silicone Hydrogel Lenses and Disinfecting Solutions
The contact lens and eyecare industry are in a transition period between HEMA lenses and silicone hydrogel lenses. The benefits of silicone hydrogel lenses have already been established and are the standard of care. Contact lens manfacturers will continue research and development to bring new lenses to market which are physically and visually comfortable to all patients. The solution manufacturers will bring to market solutions that are compatible with all silicone hydrogel lenses. The outcome will be silicone hydrogel lenses and compatible solutions which satisfy all or most patients.
What Should I Do?
Ask your Eye Doctor to be refit into a silicone hydrogel because of eye health benefits of Silicone Hydrogel Contact Lenses.
Find an MPS that works for you, whether it be Generic, Brand Name, or use Clear Care if you have sensitivities to MPS solutions.
Most people would benefit from wearing silicone hydrogel lenses as compared to conventional soft lenses due to the health advantage of higher oxygen permeability and these lenses are especially beneficial to the following patients:
- patients with higher prescriptions;
- those whose eyes show signs that they require more oxygen (neo-vasularization or edema),
- wearers who experience end of day discomfort or redness with their conventional soft lenses, and
- people who wear their lenses for more than 12 to 14 hours a day, including overnight wear.
2 Dr. Gary Andrasko http:/staininggrid.com
As in all cases, if you have questions about your contact lenses or eye health, contact your Eye Doctor. The above information is not intended to be medical advice.
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