Hydrogel Lenses and The Presbyope
CRAIG W. NORMAN, FCLSA
lens field is once again at a defining moment, a moment similar to that time in
the mid-1980s when disposable soft lenses entered the scene.
silicone hydrogel contact lenses promise improved corneal health through better
oxygen exchange. What's more, continual research has brought us materials that are
quite compatible with the ocular surface and the tear film.
With this combination, we can now offer patients safe, comfortable
options for daily and continuous wear. But what does this mean for our presbyopic
Age alone brings potential difficulties for contact lens wear
among presbyopic patients. Dry eye is not uncommon in patients over 40, particularly
postmenopausal women. In addition, poor tear quantity and quality due to aging may
be exacerbated by medical conditions and the accompanying use of systemic medications.
Near tasks, such as computer use, also contribute to dryness problems.
Tear instability has less to do with reduced tear volume and quality
of the tear layer. It is more related to the strength of tears binding to the ocular
surface and the efficiency of the blinking that re-forms the tear film. Surface-treated
silicone hydrogel lenses provide good wetting characteristics and tear deposit resistance
and, along with their lower water content as compared to conventional disposable
soft lens materials, help to provide a "wetter" contact lens. This is even more
important if overnight or continuous wear is chosen as a wearing schedule for the
Another factor to consider is that many patients in this age
group are long-term hydrogel lens wearers and may be suffering from corneal oxygen
deficiency, resulting in limbal redness and neovascularization. Silicone hydrogel
lenses have been proven to decrease these signs through improved corneal oxygenation.
Silicone hydrogels also provide a level of wearing convenience
that many presbyopes are seeking the ability to safely nap or sleep in their
Extended or continuous wear can be particularly useful for patients
such as hyperopes who have difficulty seeing up close during the lens application
and removal process and for patients who have difficulty handling contact lenses.
Latent Hyperopes Appear
Many presbyopes interested in contact lenses for the first time
are latent hyperopes manifesting the need for vision correction for the first time
both at distance and at near. It's not uncommon to need monovision lens powers
ranging from +1.00D to +4.00D in these cases. Since there's less average oxygen
transmissibility across lenses with higher plus powers, there's a great change of
corneal hypoxia among these patients. The greater oxygen exchange provided by silicone
hydrogels is ideal for these patients.
Monovision for Now
Right now, monovision is the only silicone hydrogel option for
correcting presbyopia in the United States. This may seem a step backwards for those
of us who have embraced multifocal/ bifocal soft contact lenses (although a temporary
one as will be discussed later), but for many practitioners, monovision is "business
as usual." With reported success rates of 60% to 80%, monovision remains a successful
correction option for presbyopes.
As recently as early 2005, Harris and colleagues1
reported that eyecare practitioners preferred to fit
monovision rather than bifocal contact lenses. Studies such as this, combined with
clinical experience, show monovision is still a viable alternative, particularly
for emerging presbyopes.
In addition, the recently introduced silicone hydrogel toric designs
will improve monovision success by correcting low amounts of astigmatism that we
previously were forced to mask with spherical lenses.
Given the improved oxygen exchange, the lower water content and
the surface wettability of silicone hydrogel contact lenses, practitioners definitely
should consider them for patients who are successful monovision wearers.
Multifocals in the Future
Soon, we'll have more options for the presbyope. First, we'll
see proven designs many of them familiar multifocal/bifocal designs
switched into silicone hydrogel materials.
More intriguing is the possibility of new designs and the recasting
of older styles. For instance, translating bifocal designs, which provided excellent
vision but lacked adequate corneal oxygenation when made of conventional soft lens
materials, are back on the drawing board for many researchers working with silicone
Fitting Pearl: Hydrogel to Silicone Hydrogel
Some hydrogel lens wearers may experience subclinical hypoxia,
resulting in "myopic creep." After being refitted into a silicone hydrogel lens
of the same power, these patients may be overcorrected at distance, thus increasing
their presbyopic symptoms. Make sure you follow up with these patients within a
few days of refitting to evaluate the need for a power adjustment.
Translating bifocal soft lenses, like their GP counterparts, are
quite thick because of the ballasting needed to keep the lenses in proper position
for a specific visual task. This thickness won't be as much of an issue for corneal
health with silicone hydrogel lenses due to their significantly higher Dk/t. This
should give us more options in "true" add powers and may even allow for trifocal
styles that will be helpful to computer users.
Silicone hydrogel lenses are here to stay. As with any early generation
technology, design choices may be limited right now, but we can easily add these
lenses to our presbyopic offerings for monovision candidates.
Craig Norman is director
of the Contact Lens Section at the South Bend Clinic in South Bend, Indiana. He
is a fellow of the Contact Lens Society of America and is an advisor to the
GP Lens Institute.
1. Harris MG, Kuntz S, Morris C, Zardo DF. Use of contact
lens corrections in optometric practices. CL Spectrum 2005.4:42-46.
Contact Lens Spectrum, Issue: February 2006