Diseases of the posterior segment of the eye are responsible for severe vision loss and blindness in the developed countries. The most prevalent posterior segment diseases include age related macular degeneration (AMD), diabetic retinopathy, and retinal degenerative diseases. As of 2008, AMD is prevalent in 8 million in the USA and is expected to increase to 12 million by 2020 
. Nearly 10% of the subjects suffering from AMD are diagnosed with the growth of abnormal or leaky blood vessels in the choroid below the retina, a condition known as wet AMD or choroidal neovascularization (CNV). CNV is primarily responsible for significant loss of vision and blindness in AMD patients. Diabetic retinopathy is prevalent in 4.1 million people in the United States, with nearly 22% (0.9 million) of diabetic patients having vision threatening diabetic retinopathy 
. Further, the number of diabetic patients in the USA is expected to rise to 16 million by 2050 
. Increase in prevalence of these vision threatening disorders is also resulting in a rise in the cost of treatment 
. Despite the severity and increasing prevalence of back of the eye diseases, conventional drug delivery methods are either inefficient in delivering required amount of drug to the site of action or highly invasive to the vitreous humor, with significant side effects.
The most common drug delivery method for treating ocular disorders is topical administration, primarily due to its convenience. Unfortunately, topically administered treatments are rapidly drained from the ocular surface, resulting in less than 5% bioavailability, that too mainly to the tissues in the anterior segment of the eye 
. Due to the barriers present, currently there is no eye drop formulation approved for treating back of the eye diseases. To bypass the barriers associated with topical delivery for back of the eye diseases, intravitreal injections are becoming popular 
. However, intravitreal injections are highly invasive and associated with complications such as cataract, retinal detachment, vitreous hemorrhage, and endophthalmitis 
. Other than topical and intravitreal routes of delivery, periocular routes such as sub-Tenon and subconjunctival routes can also be used to deliver drugs to the posterior segment of the eye 
. The periocular routes place the therapeutic agent adjacent to the sclera for transscleral delivery, thereby reducing the risks associated with the intravitreal route of administration 
. Nevertheless, periocular routes have disadvantages such as hemorrhage at the site of injection 
. Thus, development of a safe and efficacious route of delivery for the treatment of posterior segment disorders remains the foremost challenge in ocular drug delivery research.
Suprachoroidal space (SCS) 
is a unique, anatomically advantageous space that localizes therapeutic agents adjacent to the choroid-retina region, the target tissue affected in the neovacular form of age related macular degeneration and diabetic retinopathy. Safety of injections into the SCS was shown by Einmahl et al. 
, wherein a novel poly (ortho ester) biomaterial was evaluated, and by Poole et al., 
wherein sodium hyaluronate was injected to treat retinal detachments. Einmahl et al., 
observed that poly (ortho ester) injection in the SCS caused no clinical complications except some slight choroidal pigmentation and presence of vacuoles in the SCS. Poole et al., 
observed slight bleeding and inflammation at the site of injection, which disappeared within 3 weeks. Olsen et al. 
evaluated the safety of a novel cannula system for delivery in the SCS by monitoring histopathology and retinal and choroidal blood flow in monkeys and pigs and observed minor tissue injury at the site of injection. More recently, Patel et al. 
developed and evaluated a minimally invasive strategy using a novel hollow microneedle system to study the ex vivo suprachoroidal distribution of sulforhodamine B dye and particles ranging in size from 20 to 1000 nm. Suprachoroidal delivery is minimally invasive and might be safer because it does not require entry into the vitreous, thereby potentially protecting retina from any injection related damage.
Even though suprachoroidal delivery is being evaluated for effective treatment of posterior segment disorders, there are no reports comparing it to periocular injections. Further, there are limited investigations comparing suprachoroidal and intravitreal routes of delivery, that too for a protein drug but not small molecules 
. Since choroid vessels have high blood flow, it is generally perceived that drug molecules can clear very rapidly. Therefore, a direct comparison of different routes of drug administration will help establish the relative advantage of suprachoroidal delivery.
We used a non-invasive ocular fluorophotometry technique to study the distribution of NaF following different routes of injection. Following periocular injections, a few pharmacokinetics studies have been conducted using ocular fluorophotometry for small molecules such as NaF 
and oregon green–labeled triamcinolone acetonide 
and macromolecules such as high molecular weight FITC-dextran (40 kDa and 70 kDa) 
. Traditional methods of evaluating ocular pharmacokinetics are invasive and costly. Sacrificing animals at multiple time points followed by eye enucleation and isolation of different ocular tissues makes the process tedious and time consuming. Further, changes in drug location and concentration can occur during tissue extraction. In comparison, ocular fluorophotometry is a non-invasive technique, which does not affect ocular tissues and allows time course evaluations in the same animal in different ocular tissues using a single scan. In this study, we determined the delivery and pharmacokinetics of NaF injected in suprachorodial space of rats and compared it with intravitreal and posterior subconjunctival injections using ocular fluorophotometry. NaF is a rational choice for in vivo fluorophotometry because of its safety 
, high absorptivity, and fluorescence yield 
. Further, the molecular weight of NaF (376 Da) is similar to many antimicrobial agents and steroids administered to the eye for the treatment of ocular disorders.