BIOMECHANICAL MODEL OF THE EYE (Dr. Fedor)

Fedor‘s basic biomechanical model of the eye describes two barriers that can move independently: Lens-ciliary membrane (LCM) and Iris membrane (IM). Our concept replaces the currently used term of iris-lens diaphragm, a concept that does not reflect the findings observed during our analysis of the anterior segment ultrasound biomicroscopy (AS-UBM) images.

These two biomechanical barriers, the Lens-Ciliary membrane (LCM) and Iris membrane (IM) divide the eye in four basic compartments (K) – the anterior compartment (AK), intermediate compartment (IK), vitreous cavity compartment (VK) and lens compartment (LK).

The intraocular pressure can be different in each compartment: anterior intraocular pressure (AIP), intermediate intraocular pressure (IIP), vitreous cavity intraocular pressure (VIP) and intralenticular pressure (ILP). VIP is not to be confused with posterior pressure (PP) that is term clinically used to describe pressure from posterior direction during cataract surgery and could be result of multiple factors.

Why do we need another model of the eye? The model of independent LCM and IM better reflects the biomechanics of the eye, analyzes the volumes and pressures in the compartments and changes how we think about many eye diseases and conditions, such as glaucoma, iris plateau, hyperopia, myopia, accommodation, position and movement of IOL.

The LENS-CILIARY MEMBRANE (LCM), the main barrier that separates the anterior and posterior segment of the eye is a semipermeable membrane that contains lens, zonules, ciliary processes, ciliary body and determines the position of the IOL or the lens in the eye. LCM is a general term that could refer to lens or intraocular lens. More specific terms can be used, such as IOL-Ciliary membrane (ICM) in pseudophakic eyes or Natural Lens-Ciliary membrane (NCM) in eyes with natural lens. The LCM is a semipermeable structure that is generally permeable to aqueous fluid but impermeable to vitreous. The semipermeable area between lens and ciliary muscle is called lens-ciliary channel. Its blockage is called complete or relative ciliary block. The permeability of the LC channel can change or the area can be partially or completely obstructed by vitreous, ciliary body mass, lens remnants or other material.

The second barrier, the IRIS MEMBRANE (IM) contains the iris and stretches from iris root to the anterior surface of the lens. IM separates the anterior and intermediate compartment of the anterior segment. Its position and its movements are independent from LCM. Both membranes frequently move in similar directions, but could move in opposite direction in some cases. The lens-iris channel is a narrow space with aqueous flow and its obstruction is called complete or relative pupillary block.