Biology - Eyes

A comprehensive set of Q&A flashcards covering eye anatomy, physiology, vision mechanism, accommodation, and common defects.

What are sense organs and where is the eye located in the skull?

Sense organs are specialised structures to perceive stimuli; the eye is a photoreceptor ( photosensitive ) organ located in the eye orbit (notch of the lacrimal bone) in the skull.

What are the two eyelids called and what protection do they provide?

The upper and lower eyelids; they protect the eye and bear eyelashes on their free surfaces.

What are the two parts of the fibrous tunic of the eyeball?

Cornea and sclera (sclerotic layer).

Why is cornea transplantation usually successful?

Because the cornea is avascular (lacks blood vessels).

What is the 'white of the eye' and what is it composed of?

Sclera; white, opaque, thick fibrous connective tissue that is non-vascularised.

Name the three parts of the vascular tunic (uvea).

Choroid, ciliary body, and iris.

What is the function of the choroid layer?

Contains pigment cells and blood vessels; darkens the cavity to prevent internal reflection and nourishes the retina.

What does the ciliary body contain and what is its role?

Ciliary processes and ciliary muscles; it supports the lens and aids accommodation via suspensory ligaments.

What is the coloured part of the eye and what is the central opening called?

The iris; the central aperture is the pupil.

What are the two layers of the neurosensory tunic?

The pigmented layer and the sensory (neural) layer.

Which cells act as receptors in the retina?

Rods and cones (photoreceptors).

What pigment do rods contain and what is its function?

Rhodopsin (visual purple); enables vision in dim light.

What pigment do cones contain and what is its function?

Iodopsin (photopsin); enables color vision and discrimination in bright light.

What is the correct order of retinal neurons from photoreceptors to the optic nerve?

Rods/cones → horizontal neurons → bipolar neurons → ganglionic layer → optic nerve.

Where is the blind spot located and why?

Where the optic nerve leaves the retina; this region has no photoreceptors.

What is the macula lutea and what is the fovea?

Macula lutea is a yellowish spot near the posterior pole; the fovea is its central pit with high cone density and maximal visual acuity.

Describe the lens and its connection to the ciliary body.

A transparent, ectodermal, biconvex lens connected to the ciliary body by suspensory ligaments; these allow changing the focal length.

What are suspensory ligaments and their function?

Fibres that connect the lens to the ciliary body; they loosen or tighten to change lens curvature for focusing.

What is the anterior chamber of the eye and what fluid fills it?

The chamber between the cornea and the lens; filled with aqueous humor (an alkaline, transparent tissue fluid).

What is the posterior chamber (between lens and retina) and its fluid?

The vitreous chamber; filled with vitreous humor (gel-like, transparent).

Define accommodation in the eye.

The ability to change the focal length of the lens by changing its curvature; relaxed ciliary muscles create a flat lens for distant vision; contracted ciliary muscles create a rounded lens for near vision.

Outline the basic mechanism of vision starting from light hitting the retina.

Light triggers photopigments in rods/cones, causing chemical changes that generate receptor potentials; signals pass through bipolar and ganglion cells to the optic nerve and are processed in the brain.

What is the photopigment composition in human eyes and how does light affect it?

Photopigments are composed of opsin (protein) and retinal; light causes retinal to dissociate from opsin, altering membrane permeability and generating signals.

Where do optic nerve impulses go after leaving the retina?

To the visual cortex in the brain for processing and recognition of images.

What vitamin is essential for retinal formation and night vision?

Vitamin A (retinol).

What causes night blindness?

Deficiency of vitamin A leading to reduced rhodopsin synthesis and poor vision in dim light.

What is myopia and how is it corrected?

Nearsightedness; distant objects are blurred because image forms in front of the retina; corrected with concave lenses.

What is hypermetropia (farsightedness) and how is it corrected?

Difficulty focusing on near objects because image forms behind the retina; corrected with convex lenses.

What is presbyopia and what causes it?

Age-related loss of accommodation due to decreased flexibility of the lens or ciliary apparatus; difficulty focusing on near objects.

What is astigmatism and how can it be corrected?

Irregular curvature of the cornea causing blurred vision; corrected with cylindrical lenses.

What is cataract and how is it treated?

Opacity or cloudiness of the lens, common in older adults; treated by surgical lens replacement.

What is the role of the iris in regulating light entry to the eye?

The iris controls the pupil size; it constricts in bright light and dilates in dim light to regulate the amount of light reaching the retina.

Where is the fovea located and why is it important?

In the center of the macula lutea; densely packed cones provide the highest visual acuity.

What is the 'white of the eye' and what is its function?

Sclera; provides shape, protection, and structural support for the eyeball.

Where are the eyes positioned in relation to the nose?

The eyes are situated in the eye orbit, lateral to the nose.

Why is cornea transplantation particularly successful?

Because the cornea is avascular (lacks blood vessels), reducing the risk of rejection.

List the three main layers of the eyeball from outer to inner.

Fibrous tunic (sclera and cornea), vascular tunic (choroid, ciliary body, iris), and neural retina (pigmented layer and sensory layer).