Corneal structure, transparency, thickness and optical density (densitometry), especially as relevant to contact lens wear—a review

Abstract

Clinical instruments using Scheimpflug image-based methods to obtain optical sectional images of the cornea have been introduced in recent years along with proposals that it should be possible to routinely and reliably measure the optical density (referred to as the densitometry) of the human cornea in situ. Such a concept is reviewed from the perspective of what might be considered as the basic principles underlying the understanding of corneal transparency (from the 1950's) and the progressive changes in these ideas from subjective slitlamp-based clinical observations from the late 1960's, especially in contact lens wearers.Much more has been learned about the overall macrostructure (including corneal thickness) and the ultrastructure of the cornea from contemporary studies in the 1990's, and these aspects of the cornea will be reviewed alongside consideration of the methods of assessing the optical characteristics of the cornea in the living eye. From these perspectives, in this review systematic consideration will be given to what objective (quantitative) output one of these Scheimpflug-based systems provides and how this information might be actually related 2 to corneal transparency characteristics that might be observed clinically, particularly after long-term contact lens wear.

Change in Central corneal thickness after Phacoemulsification

“…Thickness of the cornea is an important parameter to see the endothelial cell function 4 . Positive correlation exists between endothelial cell function and Central corneal thickness (CCT) 5 . Central corneal thickness can be measured by ultrasonic pachymeter 6 .…”

Highly Transparent and Tough Filler Composite Elastomer Inspired by the Cornea

“…By combining a soft material as a matrix with an elastic material dispersed therein, a material that exhibits optical transparency and high toughness can be generated, which also is observed in biomaterials. An example is the cornea, which is one component of an eyeball. − The human cornea is a layered film with a thickness of ∼0.5 mm and consists of five or six layers. The layer called the corneal stroma, which occupies most of the cornea, is composed of a soft gel consisting mainly of mucopolysaccharide, water, and collagen fiber, which is an elastic fiber. , Since the refractive index of the collagen fibers in the visible-light region is higher than that of the mucopolysaccharide gel portion, the collagen fibers scatter visible light.…”

Influence of eye tilt on corneal densitometry

“…Alejandra Consejo 1 | Marta Jiménez-García 2,3 | Jos J. Rozema 2,3 | Ahmed Abass 4,5 induced by contact lens wear has been associated with transient increased backscatter. [18][19][20] An association of corneal densitometry with the disease has been established in multiple myeloma, 21 Fabry disease 22 and other rare disorders. 23,24 Corneal densitometry has been helpful in evaluating corneal integrity after refractive surgery, 25,26 corneal crosslinking 13 and trabeculectomy.…”