Critical Assessment of Implantable Drug Delivery Devices in Glaucoma Management

Glaucoma is a group of heterogeneous disorders involving progressive optic neuropathy that can culminate into visual impairment and irreversible blindness. Effective therapeutic interventions must address underlying vulnerability of retinal ganglion cells (RGCs) to degeneration in conjunction with correcting other associated risk factors (such as elevated intraocular pressure). However, realization of therapeutic outcomes is heavily dependent on suitable delivery system that can overcome myriads of anatomical and physiological barriers to intraocular drug delivery. Development of clinically viable sustained release systems in glaucoma is a widely recognized unmet need. In this regard, implantable delivery systems may relieve the burden of chronic drug administration while potentially ensuring high intraocular drug bioavailability. Presently there are no FDA-approved implantable drug delivery devices for glaucoma even though there are several ongoing clinical studies. The paper critically assessed the prospects of polymeric implantable delivery systems in glaucoma while identifying factors that can dictate (a) patient tolerability and acceptance, (b) drug stability and drug release profiles, (c) therapeutic efficacy, and (d) toxicity and biocompatibility. The information gathered could be useful in future research and development efforts on implantable delivery systems in glaucoma. 1. Introduction The public health burdens from ocular diseases/disorders are enormous. It is estimated that about 9.1 million American adults have one of the major retinal degenerations such as diabetic retinopathy, glaucoma, and macular degeneration. While the annual cost of adult vision problems in the US is approximately $51.4 billion including the direct medical cost, loss of productivity and other costs to caregivers and healthcare payers [1, 2]. The realization of therapeutic outcomes in ocular diseases/disorders is dependent on the ability to effectively deliver effective doses of the drugs/therapeutic agents at site of action for the intended duration of treatment. Meanwhile, the eye is a very unique vital organ that is poorly accessible to drugs/therapeutics following systemic or local administration. It is reported that only less than 5% of topically administered drug enters the eye as a result of poor permeation and extensive drug loss do occur through various mechanisms such as lacrimation, tear dilution, and tear turnover [3, 4]. Achieving the desired therapeutic outcomes from topical drug administration may be further hampered by (a) poor patient adherence to