Can it really be over ten years since the first silicone hydrogel first hit the world market with such fanfare? The lens in its various company guises soon became a favourite early on in this writer’s rooms and evolved in rapid succession from a novelty troubleshooting device to lens of first choice for most fits.
This evolution has naturally led to a vast improvement in the often troublesome area of astigmatic correction. The synergy of rapidly improved lens design from the late 90s combined with improved silicone hydrogel materials from 2000 onwards has changed this optometrica bete noire to a winning lay down misere.
The obvious benefits to patients in this area are a longer wearing and more comfortable lens with stable and high acuity vision. We are all aware of the dramatic improvement in limbal and corneal physiology a silicone hydrogel lens can bring, but as is equally noticeable with their contact lens multifocal cousins, even the most comfortable lens fit comes to nought unless there is stable and effective vision.
The four pillars of contact lens manufacture have all addressed the above problem and all have silicone hydrogel toric lenses on the market I find more than effective in addressing the issues of comfort, ocular integrity and vision. While not an overly enthusiastic advocate of an extended wear modality with these lenses, they do allow the suitable astigmatic wearer to join their fellow spherical myopic and hyperopic ametropes in seeing the digital alarm clock on waking at 3am should they so desire!
With the advent of silicone hydrogel daily disposable spherical lenses, it will only be a matter of time before a similar toric entity hits the market: Queue less storage solutions but more investment in warehousing! As with the spherical lenses for the spherical ametrope, this allows more access to contact lens wear for the part time astigmatic wearer or those averse to solutions and cleaning regimens.
Improvement in lens design has certainly led to greater ease of fitting for new and experienced practitioners alike. The stability of most 21st century toric designs allows for confidence in fitting even oblique cylindrical corrections. The acceptance - or is it the laissez faire attitude of - the moderate to high astigmat to accept reduced powers to give adequate subjective vision works with contact lenses as well. As long as the fit is stable! Today’s superb SiHy lenses allow this flexibility.
There is no point in fitting these lenses unless there is an adequate recompense to the practitioner and toric silicone hydrogel lenses can be both described and sold as premium optical devices. Place yourself in the patient’s shoes and one would be churlish indeed not to be prepared to pay a premium for a lens which not only promises but delivers both longer lasting comfort and crisp stable vision. Less chair time due to predictable fitting procedures for most designs allows for a more rapid patient turnover, further enhancing practice profitability.
Of course, with every Yin there is a Yang. For those with drier eyes and for those with various allergies, silicone hydrogel lenses in general can cause increasing intolerance, discomfort and finally rejection. While more prevalent amongst the first generation of high modulus/surface treated lenses, I still see patients who present with increasing awareness and irritation from silicone hydrogel wear using the latest third generation materials. This is usually attributable to superior palpebral conjunctival irritation, which, at its worst, develops into significant papilliary conjunctivitis (CLPC). Although this reacts well to abstinence of wear and use of over-the-counter antihistamines such as Zaditen, the patient appears to become sensitised to silicone hydrogel lens wear and will generally only have ongoing wearing success with occasional one day lens wear.
This effect is potentially more problematic for the silicone hydrogel astigmatic wearer due to the relative increase in thickness and therefore greater interaction of these lenses with the palpebral conjunctiva.
Ongoing improvements for the astigmatic wearer of silicone hydrogel lenses should thus include reducing the modulus and increasing the lubricity of materials, and increasing biocompatibility of the anterior lens surface.
The continued development and successful performance of SiHy toric lenses has certainly been a boon for this busy but happy contact lens practitioner.
In the case a patient was refitted from low-Dk spherical hydrogel lenses into high-Dk silicone hydrogel lenses to improve limbal physiology and to increase the quality of vision.
The patient - female Caucasian, 30 years old - was an experienced contact lens wearer of ten years duration with no significant medical or ocular history.
Her spectacle refraction and visual acuities were as follows:
| OD |
–4.00 / –1.25 X 100 |
6/4.8-2 |
| OS |
–3.50 / –0.75 X 85 |
6/4.8-1 |
The patient was wearing OD –4.25 D and OS –3.75 D spherical soft lenses for 15 hours per day, 7 days per week on a monthly replacement schedule. The lens fit was acceptable with good centration and movement.
The visual acuities were as follows:
| Contact lens VA |
OD |
6/7.5-2 |
| Contact lens VA |
OS |
6/6-2 |
The patient had been re-examined at various times over the ten year period.
At her first examination in my clinic the following were observed:
- Excessive limbal redness
- Blood vessel encroachment from the limbus into the clear cornea
She was refitted with toric silicone hydrogel lenses to improve the quality of vision and to increase the oxygen supply to the cornea.
She was prescribed:
| OD |
–4.00 / –1.25 X 90 |
| OS |
–3.50 / –0.75 X 90 |
At dispensing, lens fit was equivalent to that achieved with spherical soft lenses with good lens orientation and stability. Visual acuity with the SiHy toric lenses was superior compared to her visual acuity with the spherical soft lenses, and remained constant over the initial follow-up period.
| Contact lens VA |
OD |
6/4.8-2 |
| Contact lens VA |
OS |
6/4.8-1 |
The patient noticed, and was delighted with, the increased quality of her vision and the reduced level of ocular redness. Levels of comfort were similar to that of her spherical soft lenses. The patient has continued successfully to wear her toric silicone hydrogel lenses.
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