Table 2 Summary of routes of administration, applications, benefits, and challenges in ocular delivery

Systemic

Intravenous/oral

-

Uveitis, optic neuritis, ocular infection, and hypertension

High adherence among patients

Low bioavailability, BOB. Systemic toxicity is caused by excessive doses

[48]

Topical

-

On the cornea's surface

Conjunctivitis, keratitis, uveitis, blepharitis, scleritis, and episcleritis

Excellent patient adherence, self-administration, and non-invasiveness

Efflux pumps, corneal barriers, and tear dilution/turnover

[49]

Intraocular

Intracameral

In the frontal chamber

Endophthalmitis, pupil dilatation, and anaesthesia

Direct distribution to the target site, reduced dose, BRB avoidance, and increased effects

Inadequate patient compliance, The invasiveness of the medications, toxicity, consequences of puncture Haemorrhage, pain, retinal detachment, ocular pressure, and vitreous haemorrhage Endophthalmitis lens cyst development and optic nerve injury

[50]

Intravitreal

Via the vitreous body

CMV retinitis, AMD, RVO, DME, endophthalmitis, and uveitis

Subretinal

Between RPE and neurosensory retina

Cell treatment, DME, and AMD for hereditary retinal dystrophies

Intrastromal

Via the stroma of the cornea

Keratitis

Suprachoroidal

Between the choroid and the sclera

DME with uveitic macular oedema

Subconjunctival

Underneath the conjunctiva

Corneal neovascularisation and keratitis

Periocular

Posterior juxta sclera

Down to the sclera, posterior to the supertemporal limbus

Triamcinolone for DME and anecortave acetate (Retaane®) for AMD

Selective administration to both anterior and posterior portions, avoiding corneal and conjunctival obstacles, extended. duration of action

Risk of globe rupture or scarring, invasiveness, drug deposition, poor patient compliance, and consequences from punctures (pain, haemorrhage, infection) as well as injury to the nerves and muscles

[51]

Retrobulbar

Intraconal space

Anaesthesia

Peribulbar

Beyond the intramuscular septum of the four rectus muscles

Anaesthesia

Sub-tenon

The tenon capsule underneath

Chronic uveitis, macular telangiectasia, anaesthesia