hyaloid artery

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hy·a·loid ar·ter·y

the terminal branch of the primordial ophthalmic artery, which forms in the embryo an extensive ramification in the primary vitreous and a vascular tunic around the lens; by 8-1/2 months, these vessels have atrophied almost completely, but a few persistent remnants are evident entoptically as muscae volitantes.
Synonym(s): arteria hyaloidea [TA]
Farlex Partner Medical Dictionary © Farlex 2012

hy·a·loid ar·te·ry

(hī'ă-loyd ahr'tĕr-ē) [TA]
Artery in the embryo, which forms an extensive ramification in the primary vitreous and a vascular tunic around the lens; by 8-1/2 months, these vessels have atrophied almost completely, but a few persistent remnants are evident entoptically as muscae volitantes.
Synonym(s): arteria hyaloidea [TA] .
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


A tubular channel which allows the passage of air, food, blood, excretions, secretions, or anatomical structures such as nerves or blood vessels.
Cloquet's canal See hyaloid canal.
Hannover's canal A space about the equator of the crystalline lens made up between the anterior and posterior parts of the zonule of Zinn and containing aqueous humour and zonular fibres (Fig. C1).
hyaloid canal A channel in the vitreous humour, running from the optic disc to the crystalline lens. In fetal life this canal contains the hyaloid artery, which nourishes the lens, but it usually disappears prior to birth. Syn. central canal; Cloquet's canal; Stilling's canal. See hyaloid remnant.
infraorbital canal A channel beginning at the infraorbital groove in the floor of the orbit and ending at the infraorbital foramen of the maxillary bone opening onto the face below the inferior orbital margin. It is a channel for the infraorbital artery and the infraorbital nerve.
nasolacrimal canal See Table O4.
optic canal A canal leading from the middle cranial fossa to the apex of the orbit in the small wing of the sphenoid bone through which pass the optic nerve and the ophthalmic artery. Syn. optic foramen. See Table O4.
canal of Petit A space between the posterior fibres of the zonule of Zinn and the anterior surface of the vitreous humour (Fig. C1).
Schlemm's canal A circular venous sinus located in the corneoscleral junction, anterior to the scleral spur and receiving aqueous humour from the anterior chamber and discharging into the aqueous and the anterior ciliary veins (Fig. C1). Syn. scleral sinus; sinus circularis iridis; sinus venosus sclerae; venous circle of Leber. See trabecular meshwork; scleral spur; aqueous vein.
Stilling's canal See hyaloid canal.
Fig. C1 Section diagram through the anterior portion of the eyeenlarge picture
Fig. C1 Section diagram through the anterior portion of the eye


A depression or cavity below the surface level of a part.
hyaloid fossa A cup-shaped depression in the anterior vitreous body that accommodates the posterior part of the crystalline lens. It is actually separated from the lens itself by the postlenticular space of Berger. Syn. lenticular fossa; patellar fossa. See ligament of Wieger.
fossa for the lacrimal gland A depression in the frontal bone in which rests the orbital portion of the lacrimal gland, as well as some orbital fat which itself lies in the posterior part of the fossa called the accessory fossa of Rochon-Duvigneaud. The fossa is located behind the zygomatic process of the frontal bone in the anterior and lateral part of the orbital roof.
fossa for the lacrimal sac A vertical groove, some 5 mm deep and about 14 mm high, formed by the frontal process of the maxilla and lacrimal bones and which contains the lacrimal sac. The fossa is bounded by the anterior and posterior lacrimal crests coming from the maxilla (frontal process) and lacrimal bone respectively, with no definite boundary above. It leads downward to the nasolacrimal canal, which contains the nasolacrimal duct.
patellar fossa See hyaloid fossa.
trochlear fossa A small depression in the frontal bone which contains the pulley (or trochlea), a cartilaginous structure surrounded by a thick fibrous sheath 1 mm thick and through which passes the superior oblique muscle. The fossa is located about 4 mm behind the medial upper margin of the orbit.


A thin layer of tissue which covers a surface, separates cellular structures or organs, or connects adjacent structures.
basement membrane of the corneal epithelium A very thin non-cellular layer adjacent to Bowman's layer and upon which the columnar basal cells of the corneal epithelium are bound by hemidesmosomes.
Bowman's membrane See Bowman's layer.
Bruch's membrane Thin (about 1.5 μm), shiny, non-vascular layer of the choroid located on the inner side next to the retinal pigment epithelium. It consists of two contiguous layers; the inner one called the lamina vitrea (or basement membrane of the pigment epithelium) and the outer one called the lamina elastica. See angioid streaks.
Descemet's membrane 
Strong, resistant, thin (about 8 μm) layer of the cornea located between the endothelium (from which it is secreted) and the stroma. It is practically the last corneal structure to succumb to disease processes and it can regenerate after injury. Syn. lamina elastica posterior; posterior limiting layer. See descemetocele; Kayser- Fleischer ring.
Elschnig's inner limiting membrane A thin layer of astrocytes covering the optic disc. It is in continuity with the inner limiting membrane of the retina. In some cases this layer is thickened in the central part of the disc to form the central meniscus of Kuhnt. It is transparent and not usually visible with the ophthalmoscope.
hyaloid membrane This is not really a membrane, but a concentration of cells and fibres enclosing the vitreous body.
intermuscular membrane A thin, elastic membrane originating from the muscle sheath of each rectus muscle and connecting it to the neighbouring rectus muscle. The membrane fuses with the capsule of each muscle, as well as with Tenon's capsule.
nictitating membrane A fold of the conjunctival mucous membrane that can be drawn over part or all of the cornea in a winking-like action to clean and lubricate the cornea. It is present in many birds, reptiles, fishes and some mammals and is normally hidden in the inner canthus. Syn. third eyelid. See plica semilunaris.
membrane of the retina, external limiting This layer has the form of a wire netting through which pass the processes of the rods and cones of the retina. It is located between the latter and the outer nuclear layer. It is believed to be formed by the fibres of Mueller. See Mueller's cell.
membrane of the retina, internal limiting Glass-like membrane lying between the retina and the vitreous body and forming a boundary for both. For that reason it has sometimes also been considered to be the hyaloid membrane of the vitreous. The feet of the fibres of Mueller are attached to this membrane but do not form it. Syn. internal limiting layer of the retina. See Mueller's cell.
preretinal membrane See preretinal macular fibrosis.
pupillary membrane Embryonic mesodermal tissue which is present in the centre of the iris and normally disappears by the eighth fetal month to form the pupil. Some strands of the membrane may remain in adults; this is referred to as a persistent pupillary membrane.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann