Keratoconus: what is it?

Keratoconus: what is it?

Keratoconus  – This is a progressive, non-inflammatory, bilateral (but usually asymmetrical) corneal disease characterized by paraxial stromal thinning, which leads to a curvature of the cornea’s surface. Loss of vision occurs initially due to abnormal astigmatism and myopia, and secondarily due to scarring of the cornea.

In keratoconus , it is believed that all layers of the cornea change; characteristic signs are thinning of the cornea, ruptures in the Bowman’s membrane, iron deposits in the basal cells of the epithelium with the formation of Fleischer rings , folds in the stroma of the cornea, ruptures of the Descemet’s membrane, ending with acute edema.
The prevalence and incidence of Keratoconus is a relatively rare condition. Have

The level of spread of the disease according to the literature varies significantly. This is due to a variety of factors, including different levels of population surveys, tests conducted and criteria used. The frequency of occurrence ranges from 4 to 600 per 100 000 population. According to Kennedy et al . (1986) prevalence rate   —54.5 people per 100,000 population of Olmstead County in Minnesota, based on records from 1935 to 1982.

The age of onset and progression of C reports that keratoconus occurs from birth and may develop after 51 years ( Hall ). In most patients, the disease develops between the ages of 12 and 20 years.

Keratoconus usually develops first on one eye, the involvement of the second eye occurs later; usually within two years, although it may occur after 5 or 6 years. In the first eye, the disease progresses with the development of a greater curvature of the cornea. Disease of one eye is rare. In Hall was only 8 of the 288 patients who have keratoconus on the other eye did not develop for many years. On a large example of patients with keratoconus Tuft et al . found only 4.3% of patients with a follow-up of 3 years or more who had keratoconus of only one eye.

Patients diagnosed with keratoconus want to know the prognosis for disease progression and loss of vision. Doctors would also like to be able to predict the rate of development of the disease to severe keratoconus .

The progression of keratoconus in each patient individually. In some patients, the disease progresses over 6 months.   – 1 year, others   – for many years, alternating with periods of relative stabilization. In retrospect, Pouliquen analyzed case histories of 187 patients with keratoconus . He concluded that there is no relationship between the age of patients to the beginning of the disease and the degree of progression. For those who needed a cornea transplant, the average time from diagnosis to surgery was 10 years.

Woodward found that from a group of 70 patients with keratoconus (139 eyes) in 16 , 5 % of cases, corneal transplantation was required. Of the 23 eyes requiring transplantation, 21 were operated 6 years after diagnosis, and the other 2   – after 10 years.
Of all the survey data, the only correlation was found between keratometry and the need for cornea transplantation. In this case, they used the basic curvature of the contact lens, which is required for correcting the patient’s vision, since this is more accurate in cases of developed keratoconus than the distorted keratometer .

If the initial suitable contact lens had a base curve of 6 mm or steeper (bulge), in 50% of cases there was a need for a transplant. No correlation was found between age, gender and initial visual acuity and indications for transplantation. Lass et al . (1990) found in the analysis of 417 patients (746 eyes) that keratometer data more than 50 diopters and visual acuity of 20/50 or less are criteria for a possible operation.

Tuft et al . done extensive research in 2523 patients with keratoconus . They found that in 21.6% of cases, corneal transplantation is required with an average disease duration of 8.8 years (average 7 years). Patient history, objective and subjective signs. For one of the first signs of developing keratoconus for a practicing eye doctor, there may be patient complaints about the frequent change of glasses in a short period of time (12-18 months) and an increase in astigmatism.

Keratoconus affects both eyes, despite the fact that it usually develops first in one eye. Subjective symptoms normally appear between the ages of 16 and 25 years. Patients may complain that their eyes itch or that they are allergic.
In addition to reducing visual acuity, patients with keratoconus often complain of visual discomfort, like patients with uncorrected astigmatism. They are often more sensitive to light and report flare or halos around a light source, especially when driving at night.

Many even avoid night driving. Image blur, monocular doubling   – these are their usual complaints. These distortions are due to the irregular corneal shape of keratoconus .

One of the first objective signs of keratoconus is a change in the astigmatic spectacle correction in patients aged 16–25 years over several months. Increases in astigmatism are accompanied by significant changes in correction for distance and near.

An ophthalmologist can use standard office equipment to diagnose keratoconus . One such tool   – a retinoscope that can reveal the “oil drop symptom” characteristic of keratoconus . Other tool   – This is a keratometer , which measures the curvature of the cornea.

Videokeratography   – This is a technique that can be used to monitor changes in the topography of the cornea over time.
However, these tools have their limitations and they are not always accurate. Therefore, a practical eye doctor should take into account not only the data of the instruments, but also the complaints of patients and other objective signs. Biomicroscopy slit lamp About din of the earlier signs of keratoconus – Fleischer ring.

This is the ring of hemosiderin pigment , which is deposited at the base of the cone in the deep layers of the corneal epithelium. Fleischer’s ring is best seen using a special cobalt filter that gives dark blue light. Krachmer notes that the Fleischer Ring is more distinct and wider at the stage of early keratoconus and becomes thinner and more discrete as the disease progresses. In the photo below you can see a weak greenish-brown curve at the bottom of the ring against the background of a fully extended pupil.

Another characteristic feature of developed keratoconus   – These are atrophic corneal strips (marked extensions), also called Vogt strips. These are thin white lines in the stroma of the cornea. They are usually vertical and are best seen at medium or high magnification. The photo below shows the cornea at high magnification. Thin white vertical lines are visible in the center of the photo. – This is a strip of stretch marks. Small white spots on the ends of the lines   – corneal scars .

In one work McMahon et al . It was found that 98% of patients had a Fleischer ring , 60% – Vogt strips ( Vogt ) and 52% – corneal scars.

Classification of keratoconus

Keratoconus was classified according to different indicators (parameters). One classification   – According to keratometry data : Keratoconus can also be divided into weak, medium and advanced.

Weak keratoconus :
– External / corneal signs   – often absent or minimal.
– Suspicious signs   – a history of repeated inadequate spectacle correction of one or both eyes, which may include astigmatism with oblique axes and myopic refraction from medium to high degree.
– The diagnosis can be confirmed by corneal topography, which can reveal the lower steepness of the cornea (approximately 80% of cases), the central steepness of the cornea (approximately 15% of cases) or even bilateral temporal steepness (extremely rare).
– The diagnosis can also be supplemented using a diagnostic rigid contact lens with its base curvature equal to the flat value of keratometry . A typical nipple configuration is observed when staining with fluorescein .

Moderate keratoconus :
– Often there is one or more corneal signs of keratoconus :
– Corneal nerve manifestations are enhanced.
– in about 40% of eyes with moderate Keratoconus Vogt stripes develop.
– In about 50% of eyes with moderate keratoconus , iron deposits in the basal epithelial cells in the form of a ring (often incomplete) are noted on the basis of a conical protrusion called the Fleischer ring .
– in about 20% of eyes with moderate keratoconus develop scars of the cornea.
– Superficial scarring of the cornea can be fibular , nebular , or nodular.
– Deep stromal scarring may be due to dissolving mini-edema.

Some patients have scarring at the level of the Descemet’s membrane, comparable to the posterior polymorphic corneal dystrophy:

– Paraxial (usually below the pupil) thinning of the stroma may be noted.
– The values ​​of keratometry increase to 45-52 diopters .
– The distortion of the retinoscopy and the red pupillary reflex of a direct ophthalmoscopy may allow one to observe the “scissors effect” or the lower curvature, called the term “oil drop symptom”.
– Symptom Munson   – V- shaped notch   – created by the cornea on the surface of the lower eyelid when the patient is looking down. By the time it appears, keratoconus is usually already at a developed stage.

Developed keratoconus
– Often indicators of keratometry more than 52 diopters , there is an increase in all corneal signs, symptoms and loss of vision.
– Vogt strips are visible in about 60% of the eyes, Fleischer Ring and / or scarring are visible in about 70% of the eyes.
– There may be acute corneal edema.

Conservative treatment
· Hard contact lenses are the basis for the correction (treatment) of keratoconus :
– Patients with early Keratoconus can successfully use glasses or spherical / toric soft contact lenses.
– Patients with moderate to advanced keratoconus almost always prefer hard contact lenses. When hard contact lenses (CLs) are intolerable, some patients may get good vision using hydrogel CLs, CLs using the piggyback or scleral CLs, but usually at the expense of the quality of vision.
– Wearing CL is often complicated by episodes of intolerance, allergic reactions (for example, giant papillary conjunctivitis), corneal erosion, neovascularization, and other problems, sometimes leading to total (complete) intolerance.

· Surgical removal of superficial corneal scars (surface keratectomy with a blade or excimer laser) phototherapeutic keratectomy ) can improve CR tolerability, reduce the proportion of corneal concomitant erosions, and prevent corneal transplantation (transplant).
· While it is controversial to implant intrastromal corneal rings in the eyes of patients who do not tolerate contact lenses. It is more traditional to refer these patients for corneal transplantation with penetrating keratoplasty (PEP), including those whose vision is not corrected better than 20/40. PEP is very successful in the treatment of keratoconus , ensures the sphericity of the cornea in more than 90% of cases.
– After transplantation, contact lenses are often required to achieve optimal vision.
– PEP requires continuous professional monitoring of graft rejection, suture problems, wound margins and other difficulties.
– Extremely rare, but keratoconus can recur in the graft.
· Surgical treatment has been proposed, including riboflavin and ultraviolet light. With this treatment, the corneal epithelium is first removed, and the cornea stroma is treated with riboflavin and irradiated with ultraviolet light. Then the cornea is epithelized . This treatment is an attempt to cause an increase in collagen cross-linking to increase the rigidity (stiffness) of the cornea and reduce the keratoconus steepness . Treatment called cross Linking cornea (corneal collagen cross-linking).

· Developed keratoconus rarely progresses to acute corneal edema (acute keratoconus ), in which breaks occur in the Descemet’s membrane, which leads to central stromal edema and again to severe corneal scarring.
– The message of patients about sudden loss of vision and some discomfort on one eye, usually not too painful; or about conjunctival injection.   – Treatment of acute edema is palliative; many corneas flatten out after dropsy, but visual acuity and the possibility of correction of the CL can rarely improve after such events.
– If the secondary scarring of the cornea is severe, corneal transplantation (PEP) can be guaranteed.
· Patients with keratoconus develop all the complications characteristic of wearing CL, especially corneal erosion and giant papillary conjunctivitis.

· The majority of patients with keratoconus are satisfied with treatment with severe CL.
· About 10-20% of patients ultimately need corneal transplantation, but this number, it seems, will increase if there is no good treatment for CL. The latest data suggests that this disease, although progressing, will stabilize over time in the majority of patients.

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