Eyeball Anatomy

Comprehensive vocabulary flashcards covering the anatomical structures, physiological measurements, and clinical syndromes of the human eyeball based on lecture notes.

Anterior-posterior diameter

The front-to-back distance of the eyeball, which measures approximately $22\,mm$.

Optical axis

The line passing through the centre of the cornea and lens which meets the retina at the nasal side of the fovea.

Visual axis

The line joining the fixation point ($O$), the nodal point ($N$), and the fovea ($F$).

Fibrous coat

The dense strong wall of the eye protecting intraocular contents, composed of the anterior transparent cornea ($1/6\text{th}$) and the posterior opaque sclera ($5/6\text{th}$).

Limbus

The junction where the cornea and the sclera meet, and where the conjunctiva firmly attaches.

Vascular coat (uveal tissue)

The layer providing nutrition to the eyeball, consisting of the iris, ciliary body, and choroid from anterior to posterior.

Anterior chamber

A space $3\,mm$ deep bordered anteriorly by the back of the cornea and posteriorly by the iris and part of the ciliary body.

Hypermetropes

Patients who typically have a shallower anterior chamber compared to myopes.

Visual pathway

The series of structures relaying visual sensations to the occipital cortex, consisting of the optic nerve, optic chiasma, optic tract, lateral geniculate body, and optic radiations.

Corneal layers

The five layers of the cornea: Epithelium, Bowman's membrane, Stroma, Descemet's membrane, and Endothelium.

Keratocytes

Cells in the corneal stroma that produce both proteoglycans and collagen types $I, III, V, \text{and } VI$.

Corneal transparency

Maintained by uniform lamellae arrangement, avascularity, physiological dehydration, and the loss of myelin sheaths in innervating nerves.

Iris zones

Divided into the pupillary zone, containing the sphincter/constrictor muscle, and the ciliary zone, containing the dilator muscle.

Pars plicata

The anterior $2.5\,mm$ of the ciliary body where zonules attach and aqueous humor is produced.

Pars plana

The posterior flat part of the ciliary body, measuring $3.5\,mm$.

Accommodation

The process where the ciliary muscle contracts, causing zonules to relax and the lens to bulge to focus on near objects.

Blood-aqueous barrier

Formed by tight junctions of the inner non-pigmented ciliary epithelium and the non-fenestrated endothelium of iris vessels.

Blood-retinal barrier

Comprised of an inner barrier (retinal capillary endothelial tight junctions) and an outer barrier (Retinal Pigment Epithelium tight junctions).

Lens structure

An avascular structure composed of $65\%$ water and $34\%$ proteins (soluble crystallines and insoluble albuminoids).

Vitreous humour

A hydrophilic gel weighing $4\,g$ ($99\%$ water) containing type $II$ collagen and sodium hyaluronate, with a refractive index of $1.33$.

Retinal Pigment Epithelium (RPE)

The outermost retinal layer that stores Vitamin $A$ (retinol) and restores bleached rhodopsin.

Cones

Photoreceptors accumulated in the fovea and macula responsible for central and colour vision.

Rods

Photoreceptors densely packed outside the fovea responsible for night vision and peripheral vision.

Optic nerve segments

Divided into intraocular ($1\,mm$), intraorbital ($25\,mm$), intracanalicular ($4\,mm$), and intracranial ($10\,mm$) portions.

Optic chiasm

The location in the visual pathway where nasal fibers decussate while temporal fibers do not.

Relative Afferent Pupillary Defect (RAPD)

Also known as Marcus Gunn Pupil, a unilateral sensory defect often seen in conditions like optic neuritis.

Horner's syndrome

A clinical triad resulting from loss of sympathetic innervation, presenting as miosis, ptosis, and anhydrosis.

Adie's pupil

A dilated pupil with accommodation paresis caused by parasympathetic damage to the ciliary ganglion or short ciliary nerves.