An electrical stimulation apparatus for delivering therapeutic electrical stimulation to an eye of a patient, the apparatus comprising: an implantable device (1, 70, 80) comprising: an elongate substrate having a distal end, and a proximal end; and one or more electrodes (17, 77) located in or on the substrate; and a lead (3, 31, 32) through which conductors ( 33, 61) extend from the implantable device, the conductors being connected to the one or more electrodes, the lead being configured to extend from the substrate at a point at or adjacent to the proximal end of the substrate and through an incision in the surface of the eye, wherein the implantable device is configured for implanting in a suprachoroidal space between the sclera and choroid layers of the eye, wherein the substrate is configured for insertion, distal end first, via the incision in the eye to a stimulation position between the sclera and choroid layers of the eye, wherein, at the stimulation position, the one or more electrodes (17, 77) are configured for delivering electrical stimulation to the eye; characterized in that: a length of the substrate of the implantable device is configured so that, when implanted at the stimulation position, one or more distal-most electrodes of the one or more electrodes (17, 77) is located at a position beneath the retina of the eye, the substrate is not positioned beneath, and the one or more electrodes (17, 77) do not infringe on, the central retina of the eye, the length of the substrate, in a longitudinal direction of the substrate extending between the distal and proximal ends of the substrate, is between 5 mm and 13 mm. an implantable device (1, 70, 80) comprising: an elongate substrate having a distal end, and a proximal end; and one or more electrodes (17, 77) located in or on the substrate; and an elongate substrate having a distal end, and a proximal end; and one or more electrodes (17, 77) located in or on the substrate; and a lead (3, 31, 32) through which conductors ( 33, 61) extend from the implantable device, the conductors being connected to the one or more electrodes, the lead being configured to extend from the substrate at a point at or adjacent to the proximal end of the substrate and through an incision in the surface of the eye, wherein the implantable device is configured for implanting in a suprachoroidal space between the sclera and choroid layers of the eye, wherein the substrate is configured for insertion, distal end first, via the incision in the eye to a stimulation position between the sclera and choroid layers of the eye, wherein, at the stimulation position, the one or more electrodes (17, 77) are configured for delivering electrical stimulation to the eye; characterized in that: a length of the substrate of the implantable device is configured so that, when implanted at the stimulation position, one or more distal-most electrodes of the one or more electrodes (17, 77) is located at a position beneath the retina of the eye, the substrate is not positioned beneath, and the one or more electrodes (17, 77) do not infringe on, the central retina of the eye, the length of the substrate, in a longitudinal direction of the substrate extending between the distal and proximal ends of the substrate, is between 5 mm and 13 mm.