Generality
Corneal edema is a pathology of the eye characterized by an accumulation of fluid between the layers of the cornea .
This phenomenon can be observed frequently, for various reasons (including: Fuchs' dystrophy, incorrect use of contact lenses, cataract removal procedures, intraocular hypertension, etc.).
Corneal edema leads to a decrease in the natural transparency of the cornea, which results in impaired vision .
Depending on the amount of excess liquid, the corneal edema therefore results in manifestations of varying degrees, ranging from blurred vision and the perception of halos around the lights, up to the loss of visual acuity.
What's this
Corneal edema is a rather frequent pathological condition, especially in the population over 50 years of age, in which an abnormal accumulation of fluids occurs within the cornea . Fluid retention involves, in particular, the cells (keratocytes) of its central layer, ie the stroma.
Corneal edema can be widespread or localized, transient or permanent.
What is meant by edema?
In medicine, edema is a swelling of an organic tissue caused by an accumulation of fluid (especially blood serum). This can occur both outside the cells and outside the blood vessels (interstitial spaces).
Cornea: key points
- The cornea is the membrane that covers the front of the eye, through which it is possible to see the iris and the pupil.
- Transparent, avascular and convex on the outside, this structure represents the first "lens" that light meets on its way to the brain. The cornea is, in fact, an essential element of the dioptric system, as it allows the passage of light rays towards the internal structures of the eye and helps to focus images on the retina.
- The cornea consists mainly of five overlapping layers, the outermost of which is the stratified pavement epithelium, while the successive ones ( Bowman's lamina, stroma, Descemet's membrane and endothelium ) are formed by a dense weave of collagen fibrils arranged in lamellae, with a glycoprotein matrix that unites them and makes them transparent.
- The cornea performs three important functions: 1) protects the eye structures and provides them with support; 2) filters some ultraviolet wavelengths (the cornea allows light rays to pass, without these being absorbed or reflected by its surface); 3) is responsible for 65-75% of the eye's ability to make light rays converge from an external object on the fovea (central region of the retina).
Causes and Risk Factors
As briefly anticipated, the perfect transparency of the cornea is made possible by avascularity, by the structural characteristics of the stroma and by physiological mechanisms that ensure water exchange and prevent impregnation .
The optimal quantity of liquids and salts is finely regulated above all by the endothelium (ie the deepest part of the cornea). Through a system of natural "pumps", in fact, the cells of this layer play an important role in regulating the exchanges between the aqueous humor and the upper layers of the cornea (in practice, they make excess fluids escape through a true and proper flow), ensuring adequate transparency.
In any situation where the function or structure of the endothelium is altered, there is a risk of a picture of corneal edema. In practice, when a decompensation is created at this level, ie the endothelial cells are no longer able to properly regulate the water exchange, the partial or total imbibition of the tissue is determined, with thickening of the cornea and transient or permanent loss of its transparency.
Corneal endothelium: decompensation and loss of vision
The corneal endothelium consists of a single layer of cells, which have little power to regenerate after injury (they rarely divide). For this reason, when some suffer an injury, the remaining cells change shape, becoming larger, to fill the spaces left empty by those destroyed.
However, if the number of damaged cells exceeds the threshold necessary to maintain the normal functions of the cornea, the liquids filter and soak the stroma.
The resulting loss of vision depends on two main reasons:
- Changes in epithelial cells affect the refractive properties of light;
- The excess of fluids reaching the stroma disperses the incoming light and further reduces the cornea's ability to focus on the objects observed correctly.
Corneal edema: what are the main causes?
The causes of corneal edema are numerous and often result from different physiopathological processes.
Considering the role played above all by the endothelium in the maintenance of normal hydration, any pathology capable of modifying this balance and, consequently, the anatomical-functional characteristics of the other layers of the cornea, can determine an edema.
The main causal conditions include traumatic, toxic, inflammatory and dystrophic-degenerative lesions.
Diseases associated with Corneal Edema
Fuchs' dystrophy is one of the most common causes of corneal edema; this pathology of genetic origin is characterized by the gradual loss of endothelial cells.
Corneal edema can develop even in the presence of:
- Acute glaucoma (high intraocular pressure);
- Endoteliopatie;
- Inflammation of the cornea (keratitis);
- Trauma;
- Various eye infections (including ophthalmic herpes zoster).
The issues that can contribute to determining corneal edema include:
- Corneal Abrasion;
- Keratoconus;
- Severe conjunctival hyperemia;
- aniridia;
- Vitreous detachment.
Corneal edema is often a secondary side effect of eye surgery, especially after cataract removal (pseudophakic or aphakic bullous keratopathy); in this case, the condition can arise up to a few years after the procedure.
The onset of corneal edema can also be favored by the infusion of toxic drugs in the cornea or by the use of topical and systemic medicines.
Predisposing or aggravating factors
Corneal edema is quite common in contact lens wearers. The phenomenon is related to the hypoxia induced by the abuse of these devices.
Corneal edema occurs mainly after the age of fifty, especially in the presence of metabolic disorders (such as diabetes) and dry eye syndrome.
Symptoms and Complications
The symptomatology varies in relation to the site and extension of the corneal edema.
In general, a decrease in the natural transparency of the cornea causes an alteration of vision that goes from obfuscation to the loss of visual acuity. To make a comparison, the feeling of those suffering from corneal edema is to see through frosted glass.
Corneal edema: how does it manifest itself?
The most common subjective symptoms of corneal edema are fogging and vision distortion .
These manifestations may be worse in the morning (upon awakening) and tend to improve throughout the day.
Corneal edema can also involve:
- Perception of halos around light sources, especially when waking up;
- Extreme sensitivity to contact with small foreign bodies (eg dust);
- Photophobia (hypersensitivity to light).
With the progression of corneal edema, the symptoms may worsen causing:
- Eye pain that increases and worsens during blinking;
- Decreased visual acuity ;
- Irregularity in the surface of the cornea (appearance of swelling and blistering areas);
- Sensation of a foreign body in the eye .
Diagnosis
For the diagnosis of corneal edema, it is necessary to undergo an accurate eye examination . As anticipated, the severity of the symptomatology depends on the extent of the edema, that is, on how much excess liquid is present in the cornea. During the slit-lamp examination, the doctor may experience a loss of the corneal specularity. Moreover, the evaluation allows to observe an opacity or a greyish-white, localized or diffuse reflection.
The doctor could perform some tests to confirm the presence of the disease and establish the causes that led to the onset, including corneal topography and optical pachymetry, ensuring the possibility of setting an adequate medical or surgical strategy.
Treatment
The main goal of therapy is to control the extent of retention associated with corneal edema, with a concentrated saline solution and other drugs with local diuretic action . The management also plans to counteract antibiotics, the infections that can result from the accumulation of fluids.
Corneal edema: cause management
The treatment of corneal edema involves, first of all, the management of the primary cause (ie the pathology responsible for the accumulation of excess liquid).
For example:
- If corneal edema is the effect of intraocular hypertension, the therapeutic protocol is aimed at the control of the latter through the instillation of hypotensive drugs.
- If the swelling is due to a post-operative complication, the symptoms could be improved by prescribing diuretic drugs in combination with antibiotics and anti-inflammatories.
- If corneal inflammation is caused by incorrect use of contact lenses, use should be suspended.
Corneal Edema Therapy
As regards the reduction of the quantity of excess liquid, it is possible to control the extension of the corneal edema using, at the topical level, a hypertonic solution and ointments based on sodium chloride which act, creating an osmotic gradient, through the film tears outside the cornea. In other words, the instillation of these eye drops or gels, called hyperosmotic, recall the liquids out of the cornea, to make them evaporate, then, from the surface of the eye; this effect is clearly limited during the night, because - when sleeping - the eye remains closed (which is why the symptoms of corneal edema are worse in the morning). To reduce this discomfort, the doctor may advise you to apply a sodium chloride 5% ointment before going to sleep and a hypertonic solution in the morning, to remove the accumulation of liquids deposited during the night.
Patients who have significant pain can be treated with a technique known as an anterior stromal puncture .
Corneal transplantation
Unfortunately, there is no cure for improving the state of endothelial cells. In more severe cases, therefore, corneal edema requires corneal transplantation.
