When the healthy powers of vision begin to fail, we feel a tender and anxious concern to perpetuate the enjoyment we find to be so intimately dependent upon the uninterrupted exercise of sight, and are instinctively led to seek for a remedy. Much mischief will be avoided, and misapprehension removed, if we consider that in applying artificial aid to the eye, we have to do with one of our most sensitive and easily deranged organs. The human eye is composed of a series of humours and membranes: the outer coating, called the _sclerotica_ (_a_), see _Plate, Fig. 1_, is exceedingly strong, and the muscles which move the eye are attached to it; the white of the eye is a portion of this coating. The _cornea_ (_b_) arches out or projects from the eye-ball; it is transparent, and of a circular form. The next coating to the sclerotica is called the _choroides_ (_c_); it has no muscular motion except at its extremities, near the front of the eye. The _iris_ (_d_) is next apparent; it attaches itself to the sclerotica by a cellular substance called the _ciliary circle_ (_e_). According to the colour of the iris the eye is termed black, blue, hazel, &c. It is composed of two sets of muscular fibres, the one tending, like radii, towards a centre, the other forming a number of circles concentric with the same centre. The aperture in the iris is called the _pupil_ (_f_); it is always round, but varies in diameter as the radial or the circular fibres of the iris are contracted or expanded, according to the quantity and quality of light it is required to admit, acting like a watchful centinel to regulate the amount of rays requisite to transmit a perfect and well-defined image of objects onwards to the brain, which, without its agency, would appear one undistinguishable mass of confusion. The chamber of the eye is darkened by the posterior surface of the choroid membrane having a lining of dark-coloured mucus, called the _pigmentum nigrum_. The last coating of the eye is the _retina_ (_g_), a delicate and most important membrane in the construction of this noble instrument; it is an expansion of the _optic nerve_ (_h_), directly emanating from the brain; and is spread like a net of exquisite delicacy all over the surface of the choroides, terminating at the ciliary ligament. It receives the images of objects by means of the rays of light that enter at the pupil; it is transparent, but appears black on account of the dark pigmentum behind it. The optic nerve passes through a small aperture in the “_architectural dome_” containing the eye, and it conveys the impressions made on the retina into the depository of the brain, where the “very form and spirit of the scene is now conceived.” It is situated a little on one side of the centre of the eye, inclining towards the nose.