由于眼部复杂的生理结构和诸多屏障,使得全身给药后药物到达眼后段的量有限,疗效甚微.眼局部药物使用方便,但药物难以传递到视网膜.玻璃体内给药侵袭性大,危险性高.经巩膜给药有诸多优势,如巩膜表面积大,且位置表浅、操作简单,也不引起眼内屏障的损害.但要求药物在巩膜表面有适当的浓度,这个浓度过高会导致大量药物进入全身系统,引起全身不良反应;如果药物在巩膜表面浓度太低,通过巩膜进入脉络膜和视网膜所需的药物浓度梯度就难以建立.所以绝大部分药物溶液不适合经巩膜给药.为了满足巩膜表面合适药物浓度的要求,科研工作者尝试研发并使用生物材料药物微球或巩膜表面给药装置进行经巩膜给药.相比于巩膜表面给药装置,微球不需要手术植入,简单注射即可,使用较为方便.%Due to the complex of eye physiology and multiple anatomical barriers,systemically delivered drugs often cannot maintain a sustained drug level in posterior retina and vitreous.Though eye drop is convenient for patients,therapeutics that reaches retina or vitreous is very limited after topical administration.Intravitreal injection is invasive and prone to complications such as lens damage,vitreous bleeding,retinal detachment,and infection.In contrast to these routes of delivery,transscleral drug delivery has advantages such as large surface area,easy access and administration,and better safety profile without breach of the globe integrity.The challenge for transscleral delivery is that the therapeutics delivered onto the episclera needs to have an adequate concentration.If the episcleral concentration is too high,large portion of the delivered drug will be absorbed into systemic circulation and may cause systemic side effects.On the other hand,low episcleral drug concentration cannot build an effective concentration gradient for drug crossing the sclera and reaching choroid and retina.Therefore,many therapeutic compounds are not suited for transscleral delivery.In order to satisfy the proper episcleral concentration,scientists have been modulating the drug dissolution by microspheres or fabricating episcleral devices.Compared with episcleral implant or devices,episcleral microspheres do not need surgical procedure.The microspheres can be administrated by a simple needle injection.
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