Healthcare and Medicine Reference
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of a daily disposable lens that includes, in the polymerization phase, the
AquaActract biomimetic additive which functions to maintain a longer
hydration of the lens.
The use of CLs made in silicone hydrogel (SH) materials has been
proposed to manage CLRDE (Chalmers et al. 2008, Schafer et al. 2007,
Fonn 2007). SH lenses when compared with conventional lenses appear
to dehydrate less in vitro (Jones et al. 2002) and in vivo (Morgan and Efron
2003). Further, it has been demonstrated that these materials form less bonds
with protein deposits (Jones et al. 2003, Senchyna et al. 2004).
The presence of silicone in these materials makes the lens more
hydrophobic in respect to hydrogel materials with a higher affi nity for
lipid deposits (Jones et al. 2003). In order to reduce to a minimum this
phenomenon, the SH polymers have evolved starting with those that
have a surface plasma treatment (Balafi lcon A, Lotrafi lcon A, Lotrafi lcon
B, Asmofi lcon A), passing then to materials that incorporate internally
wetting agents based on PVP (such as; Galyfi lcon A, Senofi lcon A and
Narafi lcon A), and fi nally to materials that do not require either plasma
treatments or internal wetting agents (i.e. Comfi lcon A, Filcon II). Even
though not all studies have demonstrated a signifi cant difference in patient
comfort associated with the use of hydrogel conventional lenses with a
low hydration in respect to silicon hydrogel lenses (Coles-Brennan 2006,
Fonn and Dumbleton 2003), the majority of them indicate that SH lenses
are associated with better comfort (Brennan et al. 2002, Long and McNally
2006, Dumbleton et al. 2006, Chalmers et al. 2002, Chalmers et al. 2005).
Rewetting Agents
The rewetting drops have varied tasks to perform: rehydrate the CLs,
re-equilibrate the tear fi lm, and act as a lubricant. Thus it is essential that
after the drop instillation its effect must last as long as possible. Despite
their ingredients, rewetting drops tend to have a short ocular residence time,
draining through the patient's nasolacrimal duct quickly after instillation,
with the remainder being quickly absorbed by the cornea, conjunctiva, and
nasal mucosa with at least 90% loss for each instillation (Tonge et al. 2001).
For this reason, rewetting drops generally must be re-instilled frequently
throughout the day to be effective. Several investigations and clinical trials
have demonstrated the toxicity of preservatives and their allergic potential
found in the multiuse rewetting drops (Asbell and Ucakhan 2006, Baudouin
2001, Schaefer et al. 1994).
With hydrophilic CLs the risk increases because the lenses can absorb
the preservative on instillation and then release these potentially toxic
substances onto the ocular surface over a prolonged period of time. For this
reason it is important that these drops are “non-preserved”. Their different
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