Take-home message: In this article, the authors present their recent findings on drug-eluting, extended-wear contact lenses for glaucoma and discuss how these lenses may provide week-long IOP reduction with just one day of wear.
By Anuj Chauhan, PhD and Kuan-Hui Hsu
Glaucoma is known to affect around 60.5 million people worldwide and causes blindness in about 8.4 million.1, 2 Glaucoma drugs are exclusively delivered through eye drops which can be highly effective but unfortunately have a low patient compliance, particularly when more than one IOP reducing drug is required, which is true of approximately 40% of patients at five years.3 In addition to poor compliance, drug delivery via eye drops has low bioavailability due to the short residence time of just a few minutes.4 Even during the time that the tear film contains drug, a larger fraction is transported into the conjunctiva compared to the cornea due to the larger surface area and permeability.5 Only about 1-5% of the instilled drug is ultimately transported into the cornea, while the remaining fraction reaches systemic circulation through the nasal or the conjunctival route and thus can cause side effects.
Regulating IOP from space-and redefining glaucoma
Improving drug transport
To overcome all the limitations of eye drops, Dr Chauhan and his team are working towards designing drug-eluting extended wear contact lenses for glaucoma therapy. Contacts lenses are ideal for improving drug transport into the eyes for treatment of anterior diseases because of their placement in the immediate vicinity of the cornea with a thin post lens tear film in between (Figure 1). The drug molecules released from the contact lens into the post lens tear film have a long residence time of at least 30 min compared to about 2-5 min with eye drops.4 The longer residence time allows more drug molecules to transport into the cornea. The drug molecules released into the pre-lens tear film will likely be transported through the conjunctiva. Thus, it may be expected that about 50% of the drug loaded in the contact lens will reach the cornea compared to 1-5% with eye drops. This prediction is in excellent agreement with results from animal studies that have shown that contacts lenses can achieve comparable IOP reduction as eye drops with 10 to 20-fold lower drug dose. 6, 7
It is noted that other devices for glaucoma therapy such as fornix inserts or puncta plugs cannot be as effective as contacts for delivering drugs across the cornea because a large fraction of the drug released by these device will likely diffuse into the conjunctiva.
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