It refer to the developmental cataract in which the opacity occupies a discrete zone in the lens.
Genetic pattern is usually of dominant variety
Environmental form is associated with vitamin D deficiency
Sometimes maternal rubella infection contracted between 7th and 8th week of gestation may also cause lamellar cataract
Characteristic features :
Typically, this cataract occurs in the zone of foetal nucleus surrounding the embryonic nucleus.
Occasionally two such rings can be seen.
The main mass of the lens internal and external to the zone of cataract is clear, except for small linear opacities like spokes of a wheel (riders) which may be seen towards the equator.
It is usually bilateral.