Visual impairment and ocular disease are highly prevalent worldwide and can be debilitating. According to the National Eye Institute, the estimated number of people affected by the most common eye diseases will double between 2010 and 2050.1 These conditions include diabetic retinopathy, glaucoma, age related macular degeneration and cataracts. Contemporary treatment modalities for ocular disease range from conventional liquid eyedrops to invasive injection in the vitreous and surgical procedures to removal of damaged areas and implant devices.2-4
Eyedrops are the standard method for delivering medications to the front of the eye. However, eyedrops have many issues. In a landmark review, Shell illustrated that eyedrops are pulsatile delivery, with wide variations in tissue concentrations.5 This variability is undesirable, particularly chronic treatment of glaucoma with molecules of short duration of action. Eyedrops for long-term use are at the same risk of any chronic patient-administered medication, requiring treatment adherence. With respect to the application of eye drops, patient adherence to therapy is challenged by a variety of issues including drug cost, accessibility, availability, remembering to use the drop daily, convenience, iatrogenic drug discomfort or irritation, dropper tip contamination and poor vision.6 Additionally, proper instillation of eyedrops is needed which is only properly performed by a subset of patients.7-9 At times, poor communication or understanding why the medication use is recommended is the culprit of non-adherence to a prescribed therapy.10 Systemic disease such as advanced rheumatoid arthritis, poor dexterity, tremor, reduced grip strength and poor aim may make eye drop instillation difficult and bring about product waste.
Eyedrops tend to have excessive volume since they are typically 20 to 50 µL, larger than the precorneal space of approximately 7 µL.11 Typically, approximately 1-5% of applied drug is absorbed into the eye.12 Ocular drug delivery systems are designed to overcome the limitations of eyedrops in various ways, including extended residence time, decreased pulsatile delivery, controlled delivery, and more local delivery to the posterior segment. The application of scleral lenses as drug delivery devices has been illustrated with the advantage of a large fluid reservoir. Scleral lenses provide a protected environment in which the corneal surface is continuously bathed in preservative-free fluid. These lenses are inherently stable to provide lasting ocular penetration of a drug. The main detriments of scleral lenses include handling and cost, along with a variety of other complications.13
Various publications have reported the use of scleral lenses as ocular drug delivery systems. Treatment of corneal infiltrates with topical fortified non-preserved antibiotics in the bowl of the lens has been described.14 Preservative-free antibiotics in the bowl of the scleral lens worn continuously to treat persistent epithelial defects has been reported.15 Anti-VEGF agents have been used in the bowl of a scleral lens to treat corneal neovascularization.16,17 Stem cells on a scleral lens carrier for management of a chemical burn in an animal model has also been described.18
Imagine the potential future opportunities for ocular drug delivery systems with scleral lenses. On behalf of patients, hopefully imminent drug delivery systems will become successful.
2. R.G. Abell, E. Darian-Smith, J.B. Kan, P.L. Allen, S.Y.P. Ewe, B.J. Vote, Femtosecond laser-assisted cataract surgery versus standard phacoemulsificati on cataract surgery:outcomes and safety in more than 4000 cases at a single center, J Cataract Refract Surg 41 (2015) 47–52.
3. A.T. Chuang, C.E. Margo, P.B. Greenberg, Retinal implants: a systematic review, Br. J. Ophthalmol. 98 (2014) 852–856.
4. Y.X. Zhang, Y.F. Chen, X.Y. Shen, J.J. Hu, J.S. Jan, Reduction- and pH-sensitive lipoic acid-modified poly(L-lysine) and polypeptide/silica hybrid hydrogels/nanogels, Polymer 86 (2016) 32–41.
5. Shell JW. Ophthalmic drug delivery systems. Survey Ophthalmol 1984;29117-128.
6. Hennessy AL, Katz J, Covert D, Protzko C, Robin AL. Videotaped evaluation of eyedrop instillation in glaucoma patients with visual impairment or moderate to severe visual field loss. Ophthalmology. 2010 Dec;117(12):2345-52.
7. Stone JL, Robin AL, Novack GD, Covert D, Cagle GD. An objective evaluation of eye-drop instillation in glaucoma patients. Arch Ophthalmol 2009;127(6):732-736.
8. Kass MA, Hodapp E, Gordon M, Kolker AE, Goldberg I. Patient administration of eyedrops: observation. Part II. Ann Ophthalmol 1982;14(9):889-893.
9. Kass MA, Hodapp E, Gordon M, Kolker AE, Goldberg I. Part I. Patient administration of eyedrops: interview. Ann Ophthalmol 1982;14(8):775-779.
10. Slota C, Sayner R, Vitko M, Carpenter DM, Blalock SJ, Robin AL, Muir KW, Hartnett ME, Sleath B. Glaucoma Patient Expression of Medication Problems and Nonadherence. Optom Vis Sci. 2015 May;92(5):537-543.
11. Mishima S, Gasset A, Klyce SD, Baum JL. Determination of tear volume and tear flow. Invest Ophthalmol Vis Sci 1966;5264-276.
12. Tang-Liu DD-S, Liu S, Neff J, Sandri R. Disposition of levobunolol after an ophthalmic dose to rabbits. J Pharm Sci 1987;76780-783.
13. Johns, LK, McMahon JA, Barnett, M Scleral lens evaluation in Contemporary Scleral Lenses: Theory and Application. Bentham Science 2017. Volume 4 ISBN: 978-1-68108-567-8. 137.
14. Kalwerisky K, Davies B, Mihora L, et al. Use of the Boston Ocular Surface Prosthesis in the management of severe periorbital thermal injuries: a case series of 10 patients. Ophthalmology. 2012;119(3):516-21.
15. Ciralsky JB, Chapman KO, Rosenblatt MI, et al. Treatment of Refractory Persistent Corneal Epithelial Defects: A Standardized Approach Using Continuous Wear PROSE Therapy. Ocular immunology and inflammation. 2014
16. Keating AM and Jacobs DS. Anti-VEGF Treatment of Corneal Neovascularization. The ocular surface. 2011;9(4):227-37.
17. Lim M, Jacobs DS, Rosenthal P, et al. The Boston Ocular Surface Prosthesis as a novel drug delivery system for bevacizumab. Semin Ophthalmol. 2009;24(3):149-55.
18. Espandar L, Caldwell D, Watson R, et al. Application of Adipose-Derived Stem Cells on Scleral Contact Lens Carrier in an Animal Model of Severe Acute Alkaline Burn. Eye & contact lens. 2014
Dr. Barnett is a principal optometrist at the University of California Davis Eye Center in Sacramento, specializing in anterior segment disease and specialty contact lenses. She is the past president of the Scleral Lens Education Society. She is an advisor to and/or has received honoraria or travel expenses from AccuLens, Alcon, Alden Optical, Allergan, Bausch + Lomb, Contamac, CooperVision, EveryDay Contacts, Johnson & Johnson Vision, Ocusoft, Paragon Bioteck, RaayonNova, ScienceBased Health, Shire, SynergEyes, and Visioneering Technologies.