Crystalline lens
The crystalline lens (or simply, the lens, plural: lenses) is in the ocular globe between the posterior chamber and the vitreous body. It is transparent and biconvex in morphology, and aids the focusing of light onto the retina.
Gross anatomy
Location
The lens lies in the globe at the posterior aspect of the posterior chamber, superficial to the vitreous body (the posterior surface of the lens marks the boundary between the anterior and posterior segments of the globe).
Size
The neonate lens has a mass of ~65 mg, which increases to ~150 mg at the age of 10 years, and slowly grows throughout life. The lens is 10 mm in diameter, and up to 4 mm in thickness at its center .
Structure
The lens has an oval morphology, with a shallow anterior convexity, and a more marked posterior convexity. The inner lens nucleus is enclosed by a thin lens capsule. The lens is held in situ by the suspensory ligaments which run between the lens and the ciliary body.
In the child the lens is colourless, but the lens substance tends to slowly yellow with age.
Relations
- anterior: aqueous humor within the posterior chamber
- anterolateral: lens contacts the inner (pupillary) margin of the iris
- posterior: vitreous body
- lateral: suspensory ligaments, ciliary body
Function
~80% of the refraction of light occurs at the air-corneal interface. The lens forms part of the fine-tuning mechanism to ensure that incidental light is transmitted, without attenuation, and focused sharply onto the retina.
Arterial supply
- none: postnatally gases and metabolites diffuse through the aqueous humor into the lens
Venous drainage
- none: as per arterial supply, postnatally gases and metabolites diffuse from the lens into the aqueous humor
Lymphatic drainage
- none: as per arterial supply, postnatally gases and metabolites diffuse from the lens into the aqueous humor
Innervation
- postnatally there is no innervation of the lens
Histology
The lens nucleus comprises multiple fiber cells which run in an anteroposterior orientation. It has the highest protein content of any human tissue, up to 60% by weight, 90% of the proteins are lens crystallins.
Radiographic features
The lens is visible as an ellipsoid structure on cross-sectional imaging, with biconvex anterior and posterior surfaces .
Ultrasound
On ocular ultrasound the lens is anechoic with thin echogenic convexities anteriorly and posteriorly representing the capsular margins .
CT
The lens is usually well-seen on CT, even if it is a non-spiral thick-slice CT head protocol. It is a hyperattenuating (~70 HU) structure just posterior to the iris .
MRI
- T1/T1 C+: lens is slightly hyperintense relative to the aqueous/vitreous humor
- T2
- lens is best appreciated on T2 sequences
- very low signal cf. high signal aqueous and vitreous humors
History and etymology
Lens is Latin for lentil , so-called due to its similar morphology to this well-known pulse.
Related pathology
See also
