Silicone Hydrogels- Continuous Wear Tips and Success Stories

Ray Fortescue

Ray Fortescue has been in private practice in suburban Sydney Australia for over 20 years. He has a large contact lens practice with special interest in extended wear silicone hydrogel soft lenses as well as being a founding member of the Orthokeratology Society of Australia. Ray’s practice was part of Ciba Vision’s world wide clinical trial group- “First Strike” and commenced fitting continuous wear Silicone hydrogels (specifically Focus Night & Day 8.6 Base Curve) in early 1999.

Apart from regular professional presentations on a variety of topics Ray also holds positions on a number of government and semi-government authorities related to optometry and ophthalmic industry.

He is a Fellow of the Contact Lens Society of Australia, as well as holding membership of the Australasian College of Behavioural Optometrists, the Optometrists Association of Australia is a founding member of the Australian Optometric Panel and is a director of Eyecare Plus.

During our first experience with silicone hydrogels, we were "force" fitting at least 30% of patients who would have been better suited to an 8.4 base, despite this we were immediately ecstatic with our results. Silicone hydrogel lenses gave patients and practitioners the white eyes, and genuine "continuous wearability" they had dreamed of.

Prior to silicone hydrogel release, the contact lenses most used in our practice were soft disposables (Table 1). Of this less then 0.5% of patients wore their lenses on a continuous wear basis and then most cases were without our consent - generally Acuvue on a 6 night continuous wear schedule.

Table 1. Contact lens use in our practice

Today those usage statistics have changed dramatically. In four years we have increased our contact lens- related percentage of practice revenue from 8.2% in 1999 to 17.5% this last financial year. Silicone hydrogel lenses are now the most used lens type (Table 1). Obviously the growth in revenue is directly attributable to the increased usage of silicone hydrogel contact lenses in our practice!

Silicone Hydrogel Wearing Modalities

We currently have over 600 patients wearing silicone hydrogel lenses. My lens of first choice is the silicone hydrogel with the highest Dk/t. In most cases this is irrelevant but in those sensitive individuals or in high prescriptions where maximum oxygen availability is paramount this material is preferred.

There are still a considerable number of my colleagues who struggle with the concept of continuous wear - probably due to the disastrous experiences of the 1980's. After my early exposure to continuous wear with the " First Strike" trial my confidence was high. I believed in this modality- so long as both patient and practitioner were aware of the "rules" for successful wear.

Hence of my 600+ wearers, 82% are wearing these lenses on a continuous wear basis. From 7 nights to 30 nights, with the great bulk only removing their lenses on indication in the month.

The most important direction I give to wearers is to be flexible in their wearing schedules. Although they may well have 30 night continuous wear approval, if their lenses feel like they need a night or two out- after 6 nights or even 17 nights wear then they are told to "listen to your body!" Remove them! This critical understanding that if lenses don't feel right you must remove them is an integral part of our initial patient education. The incidence of CLPU's is definitely higher in those patients who stick to their rigid routines, denying physical evidence that they would be better off without their lenses- no matter how obvious those cues are. The real trick is to convince your patients that it is in fact a response to subtle cues, which will most contribute to long term successful continuous wear.

Previous editorials have mentioned many aspects of successful fits and patient choice with silicone hydrogels. I fully concur with the advice given by Alan Saks, however would add a few extra suggestions.

1/ Material Modulus/ Water Content

The compromise of water content, Dk/t and material modulus has created a differential in fitting characteristics between Focus Night & Day and Purevision.

The higher water content and lower modulus of Purevision has resulted in fitting properties more similar to conventional hydrogel contact lenses. The lens tends to 'drape' over a steeper cornea much better then the original Focus Night & Day 8.6 base. To that end Bausch and Lomb has managed with a single base curve to suit the great bulk of patients. The trade off, of course is the reduction in Dk/t of the balafilcon A material.

On the other hand Ciba Vision could not successfully fit most corneae with average K's over 44.OD with their 8.6 base. Hence the development of the 8.4 base curve. The increased modulus of lotrafilcon A can make some fits appear contradictory when comparing theoretical values and the indicated lens. I find that the choice between an 8.4 and 8.6 Focus Night & Day is governed by not only K reading (8.6<43.5D>8.4), but also by corneal diameter (sag) and importantly scleral curvature.

For example, a cornea of 42D average curvature may require an 8.4 base due to a larger corneal diameter and/or a steeper scleral curvature. The fit needs to be judged by observation of the lens edge using biomicroscopy- with and without fluorescein. The steeper (often smaller) globe results in subtle edge lift, which with the material's high modulus causes interaction with lids. A patient will often report a poorly fit Focus Night & Day as "dry" and intolerance for continuous wear.

Interestingly, my mix of Focus Night & Day base curves, has over the past 12 months come in at:

8.6 - 44%

8.4 - 56%

Further to Alan Saks' observation of unwanted corneal flattening with some hypermetropes, I too have seen approximately 12% of my Focus Night & Day hypermetropes display mild to significant corneal flattening. I postulate that the cause of this variable effect is due not only to the material's modulus, but more importantly to the space occupying properties of the optic zone of higher powered plus lenses.

In my experience, especially in presbyopic monovision patients, the near eye with higher power invariably flattens more (up to 2D). These changes are temporary and simply by ceasing continuous wear most patient's prescriptions will return to a level close to their prefitting refraction.

These characteristics of silicone hydrogel plus powered fits need to be understood and accepted or the very expensive exercise of changing progressive addition spectacle lenses to suit a transient and variable refraction will not only send you broke, but also frustrated and embarrassed.

As Alan Saks noted, it is the 50-year-old, +2.50 hypermetropic Add +2.00 who is just so excited by silicone hydrogels on a monovision continuous wear basis. Hence it is difficult with these individuals to advise them to return to daily wear- with occasional overnight wear only.

Unfortunately until the materials chemists and lens designers create a thinner, lower modulus material this phenomena will continue to cause us grief.

The other two significant fitting challenges you will encounter on a consistent basis are contact lens induced peripheral ulcers (CLPU) and contact lens induced papillary conjunctivitis (CLPC).

2/ CLPU - less than 1% of my silicone hydrogel wearers have exhibited this sign. If left unattended CLPU can become a considerable risk. One patient who did not adhere to instruction persisted through an episode of CLPU for over 72 hours before attending our rooms. Although the lesion was sterile, the physical extent was extreme with a band of limbal necrotic tissue extending from 7 o'clock superiorly to 2 o'clock. The best management strategy for CLPU is to remove a lens immediately when discomfort or an increased awareness occurs and monitor patients closely for any worsening of signs or symptoms. Practitioners should always be conservative in their approach and if in doubt use prophylactic antibiotics. A patient should never attempt to wear contact lenses through discomfort- a recipe for disaster.

3/ CLPC has been noted in less than 2% of our silicone hydrogel wearers and has definitely been less prominent in Focus Night & Day since the introduction of the 8.4 base curve. The localised nature of the condition suggests a physical trauma to tarsal conjunctiva from an imperfectly fitted relatively rigid lens edge.

Occasionally a patient will have worn their lenses inside out for a period unknowingly with a resultant persistent hypertrophy of conjunctival papillae. Often these cases need discontinuation from lens wear or generally a few months in daily disposables.

Overall these conditions aren't that prevalent, however a consistent fitter of silicone hydrogels will definitely encounter regular examples of both. You must confidently identify the problem and advise accordingly.

There have been literally hundreds of "this has changed my life" testimonials from all classes of patients which continues to invigorate our enthusiasm for contact lens practice. There have also been a few special cases and conditions which should be shared. Look into the unique characteristics of silicone hydrogel materials to help solve some of your challenging patients.

1/ R.C Female- Age 46

Presented regarding unsatisfactory spectacle prescriptions from various practitioners. Assessment of prescriptions given varied dramatically with up to -1.50 dioptres of cylinder at varying axes coming and going around a base spherical level of approximately -5.50 right and left.

Biomicroscopy revealed inferior corneal staining OU from a partial blink and lagophthalmos. Patient history revealed previous upper lid blephoroplasties (cosmetic) which coincided with her variable refraction.

The patient was fitted with a silicone hydrogel -6.50 OU on a continuous wear "bandage" basis. Within two weeks corneal exposure keratopathy had resolved and refraction was stable, with superior vision than at any time previously.

2/ J.M Male- Age 19

A sensitive young man who with R -2.50 L -2.25 was not happy wearing spectacles.

Unfortunately he had also been born with severely under developed, malformed arms with only partial claw-like hands.

At age 19 there was but one answer. He now successfully wears silicone hydrogels on a continuous wear basis with his parents both trained to remove and insert the lenses.

With his physical disabilities the further cosmetic challenges of spectacles were sufficient in this case to push him psychologically, off the edge.

The whole family is thrilled with the results.

3/ R.B Male- Age 16

Concerned with rapidly increasing myopia, intolerant of RGP contact lenses and beyond the limitations of successful orthokeratology R.B (and mother) were keen to slow the rate of myopic development.

He had been increasing at over -1.00D per year prior to fitting silicone hydrogels in January 2002.There has not been any change in power since the initial fitting.

My thoughts with regard to myopia control are that the superior optics of the high modulus silicone hydrogel materials (particularly FND) appear to almost match the results of RGP designs in slowing myopia.

Across our contact lens database the stabilising effects of silicone hydrogels on myopic increase are obvious. It would be interesting to fully investigate this apparent feature of silicone hydrogels.

One last tip to maximise the success of these products in your practice. A significant inventory of contact lens parameters is a must. Patients must be encouraged to regularly return to your practice- for both follow up ocular health assessments and also more lenses.

Ensure that those lenses are always available by maintaining a stock of all powers. I assure you this strategy will enable you to significantly grow your silicone hydrogel practice.

Finally you must believe in these materials and wearing modalities. Patients can sense a lack of conviction. If you want to succeed: believe, educate, commit, encourage and enjoy the financial and professional rewards that will ensue.