The Eye (Chapter 9)

Vocabulary flashcards covering eye anatomy, optics, retina structure, visual pathways, and concepts related to vision and acuity.

Vision

The sense of sight; involves processing light to form images and engages a large portion of the cortex.

Light

Electromagnetic radiation visible to the eye; analyzed by wavelength, frequency, and amplitude.

Wavelength

Distance from peak to peak of a light wave; determines the color of the light.

Frequency

Number of wave peaks per unit time; influences the perceived color.

Amplitude

Height of a light wave; determines the brightness or intensity.

Refraction

Bending of light as it passes into a different medium; magnitude depends on the speed difference between media.

Cornea

Glassy, transparent external surface of the eye; provides most of the eye’s refraction.

Pupil

Opening in the iris through which light enters the eye; acts like a camera aperture.

Iris

Colored part of the eye; controls the size of the pupil to regulate light entry.

Sclera

The white of the eye; tough outer layer that protects the eyeball.

Extraocular muscles

Muscles that move the eyeball within the orbit.

Optic nerve

Bundle of retinal ganglion cell axons that transmits visual information to the brain.

Lens

Transparent structure that, with the cornea, focuses light onto the retina; changes shape during accommodation.

Accommodation

The process of changing the lens shape to focus near or far objects.

Ciliary muscles

Muscles that adjust the lens to change its curvature and refractive power.

Myopia

Nearsightedness; distant objects are blurry because the focal point falls short of the retina; often corrected with concave lenses.

Hyperopia

Farsightedness; near objects are blurry because the focal point falls beyond the retina; often corrected with convex lenses.

Fovea

A pit in the center of the macula containing only cones; site of highest visual acuity.

Macula

Central retina region with relatively few blood vessels; contains the fovea.

Rods

Photoreceptors highly sensitive to low light; concentrated in the peripheral retina; not used in bright light.

Cones

Photoreceptors responsible for color vision and high visual acuity; concentrated in the fovea.

Photoreceptors

Retinal cells (rods and cones) that convert light into neural signals.

Bipolar cells

Retinal neurons that receive input from photoreceptors and relay signals to ganglion cells.

Horizontal cells

Retinal cells providing lateral connections between photoreceptors and bipolar cells; contribute to lateral inhibition.

Amacrine cells

Retinal cells providing lateral connections between bipolar and ganglion cells; modulate signal processing.

Ganglion cells

Output neurons of the retina; their axons form the optic nerve.

Lateral geniculate nucleus (LGN)

Thalamic relay that is the first synaptic stop in the primary visual pathway.

Primary visual cortex (V1)

The first cortical area to process visual information from the LGN.

Optic disk (blind spot)

Location on the retina where the optic nerve exits; contains no photoreceptors.

Inverted image

The image projected on the retina is upside down and reversed; the brain interprets it as upright.

Visual field

The area of space viewed by the retina when the eyes are fixated straight ahead.

Visual acuity

Ability to discriminate fine details; depends on photoreceptor density and accurate refraction.

Visual angle

Angular size of an image on the retina, described in degrees.

20/20 vision

Standard measure of normal visual acuity; can recognize letters at a specified distance.

Pupillary light reflex

Brainstem-controlled adjustment of pupil diameter in response to ambient light.

Consensual reflex

Contraction of both pupils when light is shone into one eye.

Ophthalmoscopic imaging

Imaging of the retina to detect diseases like glaucoma; can view macula and fovea.

Light path through the eye

Cornea → pupil → lens → retina; the cornea does most of the refraction, focusing light onto the retina.

Focal distance

Distance over which light is focused on the retina; largely determined by the cornea’s refractive power.

Cornea vs. lens refraction

The cornea provides the majority of refraction (about three times that of the lens).

Retina processing pathway (vertical)

Photoreceptors → bipolar cells → ganglion cells; the direct vertical flow of visual information.

Lateral processing (horizontal/amacrine)

Horizontal and amacrine cells provide lateral connections; influence neighboring cells and contrast.

1:1 cone to ganglion cell ratio (fovea)

In the fovea, each cone connects to a single ganglion cell, maximizing acuity.

Photopigment

Pigments in photoreceptors that absorb light and initiate the phototransduction cascade.

Ophthalmic macula and fovea relevancy

Macula is the central retina; the fovea within it provides the highest acuity vision.