Keratoconus (protrusion of the cornea) is a rare, permanently impairing and progressive disease of the cornea of the eye (which is usually round) that swells and bulges until it finally takes the shape of a cone.
This cone shape deflects the light that enters the eye and thus causes visual disturbances.
Keratoconus can occur in one or both eyes (bilaterally) and often begins during puberty or within the first 20 years of life.
Contents
Classification of keratoconus by size
- The rounded keratoconus covers up to 5 millimeters of the corneal surface (mild)
- The oval keratoconus covers 5 to 6 mm of the cornea
- The keratoglobus has an extension of over 75% of the corneal surface (severe)
Types of keratoconus based on the distance of the tip from the center of the cornea
This classification is crucial for determining the therapy and for determining the prognosis.
Grade I – Central
Grade II – Paracentral
Grade III – Peripheral
Stage IV – Pellucide marginal degeneration
Keratoconus “forme fruste” (silent form) is characterized by the presence of asymmetric astigmatism.
As a rule, keratoconus “forme fruste” remains stable throughout the patient’s life, rarely worsening and if it does, then only very slowly.
Can keratoconus damage vision?
Changes to the cornea can make it impossible to focus on near and far images.
In addition to the disturbed perception, colors are also poorly recognized.
Laser surgery to correct vision — LASIK or PRK — can be dangerous for people with keratoconus.
Causes of keratoconus and risk factors
The cause of keratoconus is unknown.
Keratoconus may be related to:
- Heavy rubbing of the eyes
- Heredity
- Some eye diseases, including retinitis pigmentosa, premature retinopathy, or keratoconjunctivitis vernalis (VKC)
- The combination of various disorders such as enzyme abnormalities or hereditary factors, including Down syndrome
- Wearing contact lenses for several years
Is keratoconus hereditary?
Genetic studies show that keratoconus is usually not hereditary, but twin research shows that the condition affects both identical twins more often than both fraternal twins.
This fact leads to the assumption that a hereditary component is possible.
Symptoms of keratoconus
In the first stages, keratoconus causes:
- a slight blur of the images
- a visual disturbance
- increased sensitivity to light (photophobia))
- Headache
- Eye pain and eye fatigue
- some patients also report burning in the eyes
- Glare, driving at night is almost impossible
When does the progression stop?
Keratoconus can progress until the age of 40, after which the situation stabilizes.
As keratoconus progresses, swelling of the cornea increases and vision progressively deteriorates.
In a few cases, the cornea suddenly swells, causing an abrupt and marked decrease in vision.
The swelling can last for weeks or months and is then replaced by fibrous scar tissue.
Signs of keratoconus
With keratoconus, some changes may occur in the eyes:
- Thinning of the cornea
- Deformation of the corneal surface
- Fleischer rings (50% of cases) – iron pigment deposition in the deeper layers of the corneal epithelium. A yellowish-green ring is formed, which becomes visible with the instruments of the ophthalmologist.
- Scars (fibrosis). Formed at the apex of the cornea as a result of rupture of the Bowman membrane. In advanced phases, they are widely spread out and can prevent the passage of light and lead to glare. The scars can also reduce the compatibility of contact lenses.
- Vogt stripes are small vertical lines (rarely distorted) that form in the deeper layers of the stroma. Pressure on the eyelids leads to the disappearance of the Vogt stripes.
- The corneal ribs become thicker and thicker in keratoconus.
- Munson’s sign is a distortion of the lower eyelid, occurs in advanced keratoconus, and can only be seen when the patient looks down.
Diagnosis of keratoconus
If keratoconus is suspected, early diagnosis is important to prevent consequential damage to vision.
The ophthalmologist may perform the following examinations:
- Keratometry
- A keratometer is used to measure astigmatism and the axis of astigmatism.
- In severe cases, keratometry may not be sufficient to make an accurate diagnosis.
- Retinoscopy is an examination in which a beam of light is directed at the retina and the reflex is evaluated.
- The deformation of the red reflection on the background (similar to an oil droplet) serves to determine the exact location of the keratoconus.
- The examination with the slit lamp serves to detect other special characteristics of keratoconus, such as the butcher’s rings (a yellow-brown-greenish discoloration) in the cornea.
- The topography of the cornea is an examination that serves to determine the curvature of the corneal surface.
- This examination works better when the keratoconus is in the initial phase, because it shows possible changes or scars on the cornea.
- Corneal pachymetry – displays the thickness of the cornea at each surface point.
Treatment of keratoconus
For the mildest form of keratoconus, glasses or contact lenses can help. However, as the disease progresses, the cornea thins and takes on an irregular shape, so that glasses or contact lenses can no longer correct vision properly.
Some authors claim that contact lenses can slow the progression of the condition, but not everyone agrees.
There is no contact lens better than another. The choice depends on how much it corrects vision and how comfortable it is.
Treatments for mild and advanced keratoconus include:
KeraSoft lenses are made of silicone hydrogel with a large water content and can correct up to 10 diopters for nearsightedness or farsightedness and up to 6 diopters for astigmatism.
These soft and customized lenses can be used temporarily by people with keratoconus who do not tolerate gas-permeable lenses for long periods of time.
Gas permeable contact lenses. If glasses and soft contact lenses cannot correct keratoconus, gas permeable contact lenses are usually chosen.
The rigid material gives gas-permeable lenses a rounded shape on the cornea, correcting the conical shape of the eye with a smooth surface that improves vision through uniform refraction.
The gas-permeable lenses are less comfortable to wear than the soft ones.
Also, the insertion of the lenses on a keratoconic eye surface is difficult and time-consuming.
One often has to visit the ophthalmologist to adjust the prescription and contact lenses (usually they are changed every 2 years), especially if the keratoconus progresses.
Mixed or piggyback contact lenses. Since gas-permeable lenses can cause discomfort, some ophthalmologists recommend piggyback lenses, i.e. two different types of contact lenses on the eye.
This method provides for the use of a soft contact lens, for example made of silicone hydrogel, and a gas permeable lens on the soft lens.
This method increases comfort for the lens wearer because the soft lens acts like one cushion among the other.
Hybrid lenses. These contact lenses have a rigid center (gas permeable) and a much softer outer ring to increase wearing comfort.
People who do not tolerate hard contact lenses can use hybrid lenses.
Scleral lenses.
These lenses are used when the cornea is too deformed or the keratoconus has progressed.
They are larger than the other lenses and cover the entire eye.
Instead of applying them to the cornea, as is the case with traditional contact lenses, the scleral lenses sit on the white area of the eye (sclera) and extend across the cornea without touching it.
Intacs (corneal implants) or intrastromal corneal ring segments
These surgically inserted corneal implants were approved by the FDA for the treatment of keratoconus in August 2004.
The plastic implants are very small and are inserted directly under the surface of the eye at the edge of the cornea to give the cornea shape again for better vision.
The Intacs may be required when patients with keratoconus cannot see with contact lenses and glasses.
Various studies show that intacs can improve the visual acuity of a keratoconic eye by two lines on a standard eye chart.
The implants also have the advantage of being interchangeable and removable.
The operation only takes about 10 minutes.
Intacs can delay but
not prevent corneal transplantation as keratoconus progresses.
Surgery for keratoconus
When to operate? Surgery may be required if:
- Corneal scars exist
- there is too much thinning of the cornea
- Visual impairment persists even with the strongest lens correction
- Contact lenses cannot be worn.
Different operations are possible, depending on the position of the cone bulge and the severity of the disease.
Crosslinking or crosslinking of the cornea
This procedure is used to stabilize the corneal tissue to stop the protrusion of the surface of the keratoconic eye.
There are two variants of crosslinking:
- With removal of the corneal epithelium When removing the epithelium
, the outer part of the cornea is removed to allow riboflavin (a B vitamin) to penetrate the cornea.
This operation cannot be performed in all patients, because the corneal thickness must be at least 400 microns.
This substance is activated with UV light, the rays of which are directed at the cornea.
Riboflavin promotes the formation of stronger collagen fibers that prevent the deformation of the cornea.
In 3-5 days, the corneal epithelium forms again. - Without removal of the corneal epithelium
This procedure is also called transepithelial crosslinking.
The corneal surface remains intact. With this method, the riboflavin needs more time to penetrate the cornea. However, there is a lower risk of infection, the method is less expensive and vision restoration is faster.
Various crosslinking clinical trials are currently underway in the United States.
Experiences of a patient after crosslinking
The eye problems started at the age of 14. Unfortunately, they develop faster when they occur very early.
At the beginning I tolerated the contact lenses and was happy, because I could see excellently.
After two years, I could no longer wear the contact lenses because my eyes became sensitive or because they became dry and peeled off.
Before the operation, I felt burning and pain.
I had two crosslinking operations.
Procedure
Crosslinking takes less than half an hour and is performed under local anesthesia (local anesthesia).
The doctor drips anesthetic drops into the eye.
The eye is kept open by an appropriate instrument.
The procedure consists in administering riboflavin drops and laser beams to the cornea.
For me, this operation was performed twice. The first time the ophthalmologist used a laser and this was not painful, but the second time he applied electric current. This technique is called ionophoresis and supports the penetration of riboflavin. This time I was in pain.
The laser procedure has brought good results, the cornea remained stable for about 5 years and I noticed a slight improvement in vision.
Unfortunately, vision has not been fully restored, but since the disease tends to deteriorate, this is an attempt to avoid or delay an invasive procedure, such as a transplant.
After crosslinking operation
Crosslinking with ionophoresis did not bring good results, vision did not improve.
The patient should spend the first two days in a darkened environment, then he can return to normal light.
It takes about a month for the results to solidify.
Crosslinking does not damage the cornea.
Surgical options for keratoconus include corneal transplantation
In the case of corneal scarring or severe dilution, a corneal transplant (keratoplasty) is usually required.
In lamellar keratoplasty, individual layers are transplanted in isolation and only part of the corneal surface is replaced.
Perforating keratoplasty is the most common corneal transplant and the entire cornea is transplanted.
In this operation, doctors remove an entire corneal area and replace it with donor tissue.
Healing after keratoplasty can take up to a year and you may need to wear rigid contact lenses for clear vision.
The definitive results regarding vision can only be seen a few years after transplantation.
What are the expectations? Prognosis for patients with keratoconus
In most cases, vision can be corrected by rigid, gas-permeable contact lenses.
Nowadays, transepithelial crosslinking can provide excellent long-term results with short recovery times.
With a corneal transplant, the results are usually good.
Recovery can take a long time and patients still need contact lenses.
