THREE LAYERS OF THE ANTERIOR SEGMENT
SPUR-IRIS-CILIARY LAYERS
The first six values of standard AS-UBM analysis describe the position of the three basic layers of the anterior segment:
1/ Spur layer (the scleral spur layer)
2/ Iris layer (the peripheral end of iris pigment epithelium layer)
3/ Ciliary layer (the ciliary processes apex layer)
TWO MEMBRANES AND 3 COMPARTMENTS OF THE EYE (FEDOR’S EYE MODEL) It is useful to think about the eye as being divided by two biomechanical barriers. Our concept of two independent barriers: Lens-ciliary membrane (LCM) and Iris membrane (IM) is replacing the currently used concept of iris-lens diaphragm and divides the eye in 3 basic compartments – Anterior compartment, Intermediate compartment and Posterior compartment.
Simply, you can think about the scleral spur as being a reference structure that does not move, the peripheral IPE point being the root of the iris membrane (IM) that moves only slightly and the apex of the ciliary processes being part of the lens-ciliary membrane (LCM) that significantly moves with accommodation or after cataract surgery compared to preoperative position.
The 3 layers of the anterior segment are based on the names of 3 points: point R - spuR (the scleral spur), point I - Iris (peripheral end of iris pigment epithelium) and point X - apeX (the apex of the ciliary processes).
Summary
Simply, you can think about
1/ the scleral spur as being a reference structure that does not move,
2/ the peripheral IPE point being the root of the iris membrane (IM) that moves only slightly and
3/ the apex of the ciliary processes being part of the lens-ciliary membrane (LCM) that significantly moves
(f.e. with accommodation or after cataract surgery compared to preoperative position) .
See more detailed information on Fedor’s biomechanical model of the eye below.