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Canalis Hyaloideus – Anatomy and Clinical Significance

The canalis hyaloideus is a narrow channel running through the vitreous body of the eye, which housed the hyaloid artery during embryonic development. It is a normal anatomical remnant.

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Things worth knowing about "Canalis hyaloideus"

The canalis hyaloideus is a narrow channel running through the vitreous body of the eye, which housed the hyaloid artery during embryonic development. It is a normal anatomical remnant.

Definition and Anatomy

The canalis hyaloideus (also known as the canal of Cloquet or hyaloid canal) is a narrow, tube-like channel that passes through the vitreous body of the eye. It runs from the posterior surface of the lens to the optic disc (papilla nervi optici) at the back of the eye. The canal measures approximately 1–2 mm in diameter and is surrounded by a thin layer of condensed vitreous tissue.

The canal is named after the French anatomist Jules Germain Cloquet (1790–1883), who first described it in the 19th century.

Embryological Significance

During the embryonic development of the eye, the canalis hyaloideus plays an essential role: it contains the hyaloid artery, a blood vessel that supplies the developing lens with nutrients. This vessel is a branch of the central retinal artery.

The hyaloid artery is detectable from approximately the 6th week of gestation.
It nourishes the growing lens and the primary vitreous.
During the third trimester of pregnancy, the vessel gradually regresses completely.
After birth, only the empty canal remains as an anatomical remnant.

Clinical Relevance

Normal Finding

In healthy adults, the canalis hyaloideus is generally clinically insignificant and difficult to visualize during a routine eye examination using a slit lamp or ophthalmoscope. It represents a completely normal anatomical structure and does not cause any symptoms.

Persistent Hyaloid Artery

In rare cases, the hyaloid artery may fail to regress completely after birth. This condition is referred to as a persistent hyaloid artery. It can occur in isolation or in association with other ocular malformations, such as persistent hyperplastic primary vitreous (PHPV), now more commonly termed persistent fetal vasculature (PFV).

A persistent hyaloid artery appears as a white or gray strand within the vitreous cavity.
It may lead to reduced vision, leukocoria (white pupillary reflex), or strabismus (squinting).
In severe cases, surgical intervention may be required.

Relevance in Posterior Vitreous Detachment

The canalis hyaloideus may play a role in age-related or pathological posterior vitreous detachment. Structural changes along the canal can influence the detachment process.

Diagnosis

The canalis hyaloideus is typically assessed during a routine ophthalmological examination. The following diagnostic methods may be used:

Slit-lamp examination with a contact or non-contact lens: Allows direct assessment of the vitreous and any visible strands.
Ophthalmoscopy: Visualization of the posterior pole of the eye and the optic disc.
Ocular ultrasound (B-scan): Particularly useful when optical media are opaque, e.g., in the presence of cataracts.
Optical coherence tomography (OCT): High-resolution imaging of the vitreous and retina.

Summary

The canalis hyaloideus is an embryologically significant but postnatally non-functional channel within the vitreous body of the eye. It is a normal remnant of fetal ocular development and has no clinical significance in the healthy adult. However, pathological variants -- in particular the persistent hyaloid artery -- can cause vision problems that may require treatment.

References

Sadler TW. Langman's Medical Embryology. 14th edition. Wolters Kluwer, 2019.
Forrester JV, Dick AD, McMenamin PG et al. The Eye: Basic Sciences in Practice. 4th edition. Elsevier, 2015.
Goldberg MF. Persistent fetal vasculature (PFV): an integrated interpretation of signs and symptoms associated with persistent hyperplastic primary vitreous (PHPV). American Journal of Ophthalmology, 1997; 124(5): 587–626.

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