Numerous novel nano-based ocular drug delivery systems have been developed to overcome the limitations of conventional drug delivery systems, which have demonstrated promising results in ocular disease models and clinical practice. Of all the nano-based drug delivery systems approved or under clinical investigation, topical instillation of eye drops is the most common route for administering therapeutics to the eye. Although this pathway is a viable way of ocular drug delivery to treat many ocular diseases because of its potential to eliminate the risks of intravitreal injection and the toxicity of systemic drug delivery, it remains a major challenge to efficiently treat posterior ocular diseases through topical administration of eye drops. So far, relentless efforts have been dedicated to the development of novel nano-based drug delivery systems with the aim of possible clinical translation. They are designed or modified to facilitate drug delivery to the retina by increasing the retention time, promoting drug penetration across barriers, and targeting specific cells or tissues. In this paper, we provided a snapshot of nano-based drug delivery systems that are currently marketed and under investigation in clinical trials for the treatment of ocular diseases and highlighted some examples of recent preclinical research on novel nano-based systems as eye drops to the posterior segment of the eye.