Visual System and Photoreception Practice Flashcards

A Comprehensive collection of vocabulary and key concepts from the lecture notes on the visual system, including eye anatomy, photoreception mechanisms, visual defects, and eye movements.

Visible Light

Electromagnetic waves with wavelengths between $400-700\,nm$ that the human eye can detect.

Cornea

The transparent anterior portion of the sclera that bends light entering the eye before it reaches the lens.

Optic Nerve (Cranial Nerve II)

The nerve that connects the eye to the brain and pierces the back of the sclera.

Choroid Melanin

A pigment within the middle vascular layer that acts as a light-absorbing layer to prevent internal reflection within the eyeball.

Iris

The pigmented anterior portion of the choroid that gives the eye its color and contains antagonistic circular and radial smooth-muscle fibers.

Macula Lutea

A small, yellowish central portion of the retina.

Fovea Centralis

A depression in the center of the macula lutea containing only cones; it is the fixation point with the sharpest, most acute visual acuity.

Vitreous Humor

A gelatinous semi-solid substance that fills the posterior cavity and maintains intraocular pressure to prevent the eyeball from collapsing.

Aqueous Humor

A clear and watery fluid secreted by the ciliary epithelium into the posterior chamber of the anterior cavity.

Canal of Schlemm (Scleral Venous Sinus)

A drainage canal where aqueous humor flows out from the trabecular meshwork.

Glaucoma

A condition where aqueous humor production exceeds drainage, increasing intraocular pressure and causing damage to the retina and optic nerve.

Refractive Media of the Eye

The four structures responsible for bending light: the cornea, aqueous humor, lens, and vitreous humor.

Accommodation

The act of physiologically adjusting crystalline lens elements to alter refractive power and bring objects at different distances into sharp focus.

Near Point of Vision

The nearest point to the eye at which an object can be brought into clear focus by accommodation, often taken to be $25\,cm$.

Presbyopia

An age-related decline in the ability to accommodate due to the ciliary body muscle and lens gradually losing elasticity.

Near Response

A three-point response to near objects consisting of accommodation, convergence of the visual axes, and constriction of the pupil.

Myopia (Nearsightedness)

A condition where light is focused in front of the retina because the eyeball is too long or the cornea has too much curvature; corrected with biconcave lenses.

Hyperopia (Farsightedness)

A condition where light converges behind the retina because the eyeball is too short or the lens has insufficient power; corrected with convex lenses.

Astigmatism

A defect occurring when the curvature of the cornea or lens is uneven, corrected with spherocylindrical lenses.

Cataract

The opacity or clouding of the lens caused by the clumping together of alpha crystallins proteins.

Horizontal Cells

Interneurons in the retina that aid in signal processing and provide lateral connections between photoreceptors and bipolar cells.

Rods

Dim light receptors ($<0.1\,foot-candles$) providing scotopic (night) vision; they account for $95\%$ of light receptor cells in the retina.

Cones

Photoreceptors responsible for color (photopic) vision that have a higher threshold for light than rods.

Rhodopsin

A purple colored visual pigment in rods made from 11-cis retinal covalently linked to scotopsin.

Dark-current

The influx of $Na^+$ and $Ca^{2+}$ through CNG channels in the dark, which keeps the photoreceptor membrane potential slightly depolarized ($-30\,mV$).

Phototransduction Cascade (Light)

Activation of metarhodopsin II activates transducin, which activates phosphodiesterase (PDE) to hydrolyze cGMP, leading to the closure of CNG channels and hyperpolarization of the cell ($-90\,mV$).

Iodopsin

The violet colored visual pigment in cones, made from 11-cis retinal linked to photopsin.

Optic Chiasm

The location where optic nerves converge and fibers from the nasal hemiretinas cross the midline.

Bitemporal Hemianopia

Blindness in both temporal half-fields caused by damage in the optic chiasma involving crossing nasal fibers.

Ishihara Test

A commonly used test to detect color blindness or color vision deficiency.

Nyctalopia (Night Blindness)

An inability to see in dim light caused by a deficiency in Vitamin A, which impairs dark adaptation.

Pupillary Light Reflex

The reduction of pupil size in response to light, involving the pretectal nucleus and Edinger-Westphal nuclei.

Saccades

Rapid, ballistic eye movements that abruptly change the point of fixation.

Smooth Pursuit Movements

Slow tracking eye movements designed to keep a moving stimulus on the fovea.

Vestibulo-ocular Movements

Reflex responses that stabilize the eyes relative to the external world by compensating for head movements.