When looking at objects that are close, the lens of the eye must “thicken” to accommodate changes in depth of field. This is accomplished by contraction of the ciliary muscle, which allows the suspensory ligament to stretch. The lack of tension then allows the lens to draw up into its thicker resting state. If the vision is shifted to a far object, then ciliary muscles will relax, which increases tension on the lens via the suspensory ligament and causes it to "flatten." The lens does not “tilt” or “rotate.”

Ciliary and pupillary muscles are innervated by CN III, the oculomotor nerve. This nerve is also responsible for elevation of the upper eyelid, and innervation of the superior rectus, medial rectus, inferior rectus, and inferior oblique muscles of the eye. The abducens nerve (CN VI) innervates a single extraocular muscle: the lateral rectus. The optic nerve is primarily involved in transmission of visual signals from the retina to the brain, and the trigeminal nerve is not directly involved in ocular movement or function.

The fovea centralis is a zone of densely packed cone cells in the center of the macula lutea of the retina. Because of this it is the region capable of the highest degree of visual acuity. The optic disc is the point of exit for ganglion cell axons of the optic nerve. This is an area absent of rods or cones, and so is considered a "blind spot" of the eye. Last, the cornea and lens are not part of the retina.

Cones are the primary photoreceptor cells responsible for transmitting information about color. They are the only photoreceptor cell type that is capable of differentiating between colors. Rod cells are not capable of color vision and primarily transmit information in regards to contrast. They are most active in very low light, while cone cells are most active in levels of high light. This is why it is difficult to perceive color at very low light levels. Photosensitive retinal ganglion cells do not transmit visual information to the brain - rather, they are involved in physiological processes such as pupillary reflex and circadian rhythms. 

The light sensitive cells of the retina are called "photoreceptor cells." This is a group of cells with various functions regarding the transmission of information about brightness, color, and contrast. None of the other structures listed are cell types of the eye.

“Rods” are incredibly sensitive to light, and can be triggered by a single photon. These cells are the primary photoreceptor cells active at very low light. The activation of cone cells requires significantly larger amounts of photostimulation; therefore, they function primarily in interpreting visual information in bright light. Photosensitive retinal ganglion cells, a group of cells that make up a very small percentage of overall photoreceptor cells, are less sensitive to photons and have a slower response time than either rods or cones.

There are three types of photoreceptor cells in the retina: “rods,” “cones,” and “photosensitive retinal ganglion cells.” While rods and cones directly communicate information about sight (e.g. contrast, brightness, and color), photosensitive retinal ganglion cells do not directly communicate visual information to the brain. Rather, they are involved in the pupillary reflex.

Myopia is nearsightedness, meaning the focal length is too short. This can be caused by too much refraction at the eye's lens or if the eyeball is too long. Myopia can be corrected using a concave (i.e. diverging) lens, which will increase the focal length as shown in the figure. 

Weber's law states that the change in a stimulus that will be just noticeable is a constant ratio of the original stimulus. Because the original stimulus changes in each condition (i.e. low, medium, high), the ratio for the just-noticeable difference also changes; therefore, the magnitude necessary to detect a change will vary by condition. 

The eyes contain approximately seventy percent of the total sensory receptors of the body. Most of these are located in the retina, which has up to 200,000 photoreceptor cells per square millimeter in its densest location (i.e. the fovea centralis).