Chapter 15

Fibrous layer of the eyeball

Outermost layer; dense avascular connective tissue consisting of two regions: sclera and cornea.

Vascular layer of the eyeball

Middle pigmented layer consisting of three regions: choroid, ciliary body, and iris.

Sensory layer of the eyeball

Retina: Outer pigmented layer and neural layer, which contains photoreceptors that transduce light energy.

Rods

Photoreceptors more numerous at the peripheral region of the retina that operate in dim light and provide indistinct, fuzzy, non-color peripheral vision.

Cones

Photoreceptors found in the macula lutea, concentrated in the fovea centralis, that operate in bright light and provide high-acuity color vision.

Pathway of light entering the eye

Cornea, aqueous humor, lens, vitreous humor, neural layer of retina, photoreceptors.

Accommodation

Active adjustment where the lens shape is changed by ciliary muscles to increase refractive power.

Emmetropic

Normal vision where the focal point is on the retina.

Myopic

Nearsighted vision where the focal point is in front of the retina.

Hyperopic

Farsighted vision where the focal point is behind the retina.

Pitch

Perception of different frequencies of sound, with a normal range of 20-20,000 Hz.

Loudness

Subjective interpretation of sound intensity, with a normal range of 0-120 decibels (dB).

Static equilibrium

Monitored by vestibular receptors.

Dynamic equilibrium

Monitored by semicircular canal receptors.

Cataracts

Clouding of the lens, often age-related, with risks including diabetes, smoking, and prolonged sunlight exposure.

Glaucoma

Condition involving pressure buildup in the eye that can cause blindness by affecting the retina and optic nerve.

Macular degeneration

Progressive deterioration of the retina and a main cause of vision loss in individuals over 65.

Deafness

Hearing loss that can be either conductive or sensorineural, with cochlear implants available for cochlear damage.