Cornea stroma

When the corneal epithelium is breached by injury, the barrier to fluorescein penetration is lost, and it can diffuse into the underlying cornea stroma. Thus, detection of the presence of fluorescein staining is valuable for the detection of early comcal injury. This i.s facilitated by examination under ultraviolet light or by using a blue filter in a slit-lamp biomicroscope. 

The cornea is the first structure of the eye to be in contact with incident light. It is composed of five distinct layers lying parallel to its surface the outer epithelium, which is continuous with the epithelial layers of the conjunctiva the epithelial basal lamina the keratocyte-containing stroma, which is a collagen structure arranged so that it is transparent Descemet s membrane and, finally, the endothelium adjacent to the aqueous humour. 

Cornea Epithelium Bowman s membrane Stroma (substantia propria) Descemet s membrane Endothelium... 

Microscopically, the cornea shows a rather simple and multilayered structure that can be divided into six layers the epithelium, basement membrane, Bowman s layer, stroma, Descemet s membrane, and endothelium. The corneal tissue consists of three different cell types epithelial cells, keratocytes (corneal fibroblasts), and endothelial cells. The outermost corneal surface is covered with the preocular tear film, which is functionally associated with the cornea. The epithelial surface must be kept moist and smooth, a role played by the tear film in conjunction with a spreading function of the eyelids during blinking motions. Furthermore, the tear film provides a protection against infectious agents that may gain access into the eye. 

As another extracellular component in the cornea, the Bowman s layer is an acellular and amorphous band between the corneal epithelium and stroma. The layer is about 8-12 [im thick and consists of randomly arranged collagen fibers (types I and III) and proteoglycans. The physiological function of Bowman s layer is not yet completely understood, since not all animal species exhibit this membrane in the corneal structures, but an important role in the maintenance of the corneal epithelial structure is expected or probable, since a damaged Bowman s membrane usually results in scarring during wound repair [16],... 

In another approach, Parnigotto and coworkers reconstructed corneal structures in vitro by using corneal stroma containing keratocytes to which corneal epithelial cells from bovine primary cultures were overlaid [73], However, this particular corneal model did not contain an endothelial layer. This model was histochemically characterized and the toxicity of different surfactants was tested using MTT methods. This stroma-epithelium model has been reported to show a cornea-like morphology, where a multilayered epithelial barrier composed of basal cells (of a cuboidal shape) and superficial cells (of a flattened shape) is noted. Furthermore, the formation of a basement membrane equivalent and expression of the 64-kDa keratin were reported, indicating the presence of differentiated epithelial cells. The toxicity data for various surfactants obtained with this model correlate well with those seen by the Draize test [73], However, this corneal equivalent was not further validated or used as a model for permeation studies. 

In an accidental exposure, a blast of vapor that struck the eye of a student caused the epithelium to be lost from the cornea. There was no edema of the corneal stroma, and the eye was completely normal within 4 or 5 days the exposure was thought to be minimal. 

The acute pathologic effects of H on the eye include edematous clouding of the cornea and necrosis of corneal stroma. About 5 h later, infiltration by segmented leukocytes is noted at the sclero-comeal junction and in the corneal stroma. Healing usually occurs in several weeks, but the Injury may result in persistent or recurrent corneal ulceration and blindness. 

The normal cornea contains 75-80% of water, with a 3.4 ratio weight of water in the stroma/dry weight. In physiological conditions, the cornea must permanently fight against hydric imbibition in order to maintain a constant thickness and keep its transparency. It is said to be in a state of deturgescence. 

On the other hand, the cornea is located between two hypertonic grounds tears and the aqueous humor. The rules of osmotic balance are a good explanation for the passive move of water toward the front and back sides of the cornea, so contributing in the maintenance of the relative dehydration of the stroma. 

Nevertheless, the stroma might also have some ability to regenerate the cornea. That is what the Thill and his assistant study [7] seems to demonstrate with the highlighting of a new population of repairing stem cells located inside the adult human corneal stroma. These cells might evolve toward the monocyte-macrophage specie or toward the ti broblast specie (keratocytes). 

Cintron, C. The molecular structure of the comeal stroma in health and disease. In Chandler, J.W., Sugar, J., Edelhauser, H.F. (eds.) External Diseases Cornea, Conjonctiva, Sclere, Eyehds, Lacrimal System, vol. 8. Mosby, London (1994)... 

The stroma of cornea and conjunctiva consists of connective tissue, which in the conjunctiva is extremely soft, containing superficial and deep vessels on the sclera located in arterial and venous vessels. 

These vessels end in arcade-like structures at the limbus. The corneal stroma is made of three different main layers that differ in density of collagen and type of packing. The Bowman s membrane of the anterior stroma is part of the basal membrane of the corneal epithelium and accounts for 5% of the thickness of the central 500-600 pm cornea. The corneal stroma consists of highly ordered, horizontally organized and noninterconnected coUagen I and X fibriUae that are kept in a hydrated state with a water content of 72-78% and an osmolarity of 420 mOsmol/kg [1]. 

The inner layer of the corneal stroma is a dense membrane of collagen like the basal membrane of the monolayer of corneal endothelium. Descemets membrane is transparent with a thickness varying from 7 to 20 pm, according to the age of the individual. Conjunctiva and cornea host nerve endings of high density in the snperhcial and basal layers. The cornea at the limbns smoothly changes to sclera with interconnected nontransparent collagen hbrils. 

In several experiments, we have measured the comeal stroma and intracameral osmolarity by means of cryo milhng and redilution of the stroma of the burnt cornea and by direct measurements of the intraocular fluids. 

We have observed the following pattern (Fig. 6.2) of decrease of the tissne osmolarity after eye bnms within the comeal stroma. This confirms the chnical finding of severe edema of the stroma and was snstained by work of Kompa et al. [8], who have found the alteration of the comeal sweUing and comeal osmolarity by the eye bnm itself and changes due to different fluids used for rinsing of the cornea thereafter. 

The histological architecture of the cornea and specifically that of the stroma. 

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