Table 2. The localization of various ocular membrane transporters and their ocular drug substrates.

Gene	Protein Name	Ocular Drugs	Route of Administration	Transport		Localization		References
				Direction*	Mechanism	Previous Study	Current Study
SLC15A1	PEPT1	amoxicillin, valacylovir	topical, oral	Absorptive	H+-coupled symporter	iris, ciliary body, cornea	choroid, cornea, retina	[30, 66-68]
SLC15A2	PEPT2	amoxicillin	topical	Absorptive	H+-coupled symporter	cornea, retina, choroid, ciliary body, iris	none	[30, 66]
SLC22A1	OCT1	ganciclovir, acyclovir, atropine	topical, systemic	Absorptive	Electrogenic, Na+ -independent	cornea, retina, choroid, iris, ciliary body	choroid, cornea	[30, 69, 70]
SLC22A2	OCT2	acyclovir, ganciclovir, atropine, epinephrine	topical, systemic	Absorptive	Electrogenic, Na+ -independent	iris, ciliary body	choroid, ciliary body, cornea, iris, retina	[30, 69-72]
SLC22A3	OCT3	verapamil, bromonidine, atropine, epinephrine	topical	Absorptive	Electrogenic, Na+ -independent	cornea, retina, choroid, iris, ciliary body	choroid, ciliary body, cornea, iris, retina	[30, 69, 72, 73]
SLC22A4	OCTN1	verapamil	topical	Absorptive	Electrogenic, Na+ -independent	cornea, retina, choroid, iris, ciliary body	none	[30, 74]
SLC22A5	OCTN2	verapamil	topical	Absorptive	Electrogenic, Na+ -independent	cornea, retina, choroid, iris, ciliary body	choroid, ciliary body, cornea, iris, retina	[30, 75]
SLC22A6	OAT1	cefazolin, penicillin G, tetracycline, acyclovir, cidofovir, ganciclovir, zidovudine	topical, oral, systemic	Absorptive	Organic anion/dicarboxylic acid exchanger	retina, iris, ciliary body	choroid, cornea, iris	[30, 70, 76-80]
SLC22A7	OAT2	acyclovir, cefazolin, penicillin G, tetracycline, erythromycin, zidovudine, 5-fluorouracil	topical, oral, systemic	Absorptive	Organic anion/dicarboxylicacid exchanger	none	cornea	[30, 70, 81-83]
SLC22A8	OAT3	cefazolin, penicillin G, tetracycline, acyclovir, valacyclovir, zidovudine	topical, oral, systemic	Absorptive	Organic anion/dicarboxylic acid exchanger	retina, choroid, iris, ciliary body	choroid, cornea, iris	[27, 30, 70, 76, 81]
SLC22A11	OAT4	cefazolin, penicillin G, zidovudine, diclofenac, tetracycline	topical, oral	Absorptive	Organic anion/dicarboxylic acid exchanger	ND	none	[70, 76, 81]
SLC22A12	URAT1	unknown				ND	none
SLC47A1	MATE1	ganciclovir, acyclovir	topical, systemic	Absorptive/Secretive	H+-coupled antiporter	ND	iris	[84]
SLC47A2	MATE2	ganciclovir, acyclovir	topical, systemic	Absorptive/Secretive	H+-coupled antiporter	ND	cornea	[84]
SLCO1A2	OATP1A2	dexamethasone, erythromycin, levofloxacin	topical	Absorptive	Na+-independent exchanger	retina, choroid	choroid, ciliary body, iris, retina	[30, 85, 86]
SLC10A1	NTCP	unknown				ND	choroid, ciliary body, cornea
SLC10A2	ASBT	unknown				none	choroid, iris, ciliary body, cornea, retina
SLCO1B1	OATP1B1	unkown				none	choroid, ciliary body, cornea, iris
SLCO1B3	OATP1B3	Cyclosporine A, penicillin G	topical, systemic	Absorptive	Na+-independent exchanger	retina	choroid, ciliary body, retina, cornea, iris	[87]
SLCO2B1	OATP2B1	Cyclosporine A	topical	Absorptive	Na+-independent exchanger	cornea, retina, choroid, iris, ciliary body	choroid, ciliary body, cornea, iris	[30, 86, 88]
ABCB1	MDR1/PgP	Cyclosporine A, erthromycin, acebutolol, timolol, levofloxacin, miconazole, dexamethasone, hydrocortisone, prednisolone, verapamil	topical, oral	Secretive/Efflux	ATP-dependent efflux pump	cornea, retina, choroid, iris, ciliary body	choroid, iris, ciliary body, retina, cornea	[27, 30, 89-95]
ABCB11	BSEP	unknown				ND	choroid, ciliary body, cornea, retina
ABCB4	MDR2	verapamil	topical	Secretive/Efflux	ATP-dependent efflux pump	ND	ciliary body, cornea	[96]
ABCC1	MRP1	glutathione and glutathione conjugates, leukotriene C4, estradiol-17-beta-o-glucuronide, erythromycin, clotrimazole	topical	Secretive/Efflux	ATP-dependent efflux pump	cornea, retina, choroid, iris, ciliary body	iris, ciliary body, retina, cornea	[30, 89, 90]
ABCC2	MRP2	erythromycin, acyclovir	topical, systemic	Secretive/Efflux	ATP-dependent efflux pump	retina, choroid	choroid, cornea	[30, 89, 90, 93, 97, 98]
ABCC3	MRP3	unknown				cornea, retina, choroid, ciliary body, iris	cornea	[89, 90]
ABCC4	MRP4	ganciclovir, zidovudine	topical, oral	Secretive/Efflux	ATP-dependent efflux pump	ND	choroid, iris, ciliary body, cornea, retina	[89, 90]
ABCC5	MRP5	bimatoprost, latanoprost, acyclovir, 5-fluorouracil	topical, systemic	Secretive/Efflux	ATP-dependent efflux pump	cornea, retina	choroid, iris, ciliary body, retina, cornea	[89, 90, 98, 99]
ABCC6	ARA	unknown				ND	cornea
ABCG2	BCRP	acyclovir, cyclosporine, ciprofloxacin, norfloxacin, ofloxacin, zidovudine, dexamethasone, trimcinlone	topical, systemic, oral	Secretive/Efflux	ATP-dependent efflux pump	cornea, retina, ciliary body, iris, choroid	ciliary body, retina, cornea, choroid	[30, 89, 90, 100]

ND, not determined.

^*SLC transporters can function bidirectionally; therefore direction depends on the chemical gradient of the substrate and where applicable the gradient of the co-transported or counter-transported ion.