Crystalline lens

The crystalline lens (or simply, the lens) 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.

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 centre ^3,6.

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 humour 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

Postnatally there is no blood supply to the lens: gases and metabolites diffuse through the aqueous humour into the lens. Similarly the lens lacks venous or lymphatic drainage.

Innervation

Postnatally there is no innervation of the lens.

Histology

The lens nucleus comprises multiple fibre 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 ⁴. 

Ultrasound

On ocular ultrasound the lens is anechoic with thin echogenic convexities anteriorly and posteriorly representing the capsular margins ⁷. 

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 structure(~70 HU) structure just posterior to the iris ⁸. 

MRI

• T1/T1/T1 C+: lens is slightly hyperintense relative to the aqueous/vitreous humour
• T2
  • ​lens is best appreciated on T2 sequences
  • very low signal cf. high signal aqueous and vitreous humours

History and etymology

Lens is Latin for lentil ², so-called due to its similar morphology to this well-known pulse.

Related pathology

• aphakia
• cataract
• lens dislocation

See also

• globe