What is keratoconus?
Keratoconus is a non-inflammatory, bilateral (but generally asymmetric) disease of the cornea that progresses to a corneal erection. It is characterized by paracentral corneal thinning and ketosis so that the cornea acquires a cone shape. Visual damage is mainly caused by myopia and irregular astigmatism and, secondly, by corneal scarring.
In 1729, Dudley described a patient with a protruding conical cornea and poor eyesight. Keratoconus was originally defined broadly based on the shape and position of the cone. These include round or nipple cones and oval cones with a central conical bulge, often crumbling.
Mark Amsler was the first to describe early corneal topographic changes in keratoconus patients using a keratoscope/Placido disc (an eye device to detect abnormal curvature of the cornea). He classified keratoconus into clinically identifiable stages:
Hidden stage: The hidden stage is detected only by the placental disc.
Initial phase: The initial phase is divided into two categories:
- Keratoconus frost, which causes a deviation of 1 to 4 degrees from the horizontal axis of the placental disc.
- Early or mild keratoconus, which causes a deviation of the horizontal axis of 5 to 8 degrees.
- Conical cornea
Causes of keratoconus
The cause of keratoconus is unknown. It may not be a single disorder, but it is an asymptomatic expression of many causes, both genetic and environmental.
The inheritance pattern of keratoconus is not completely defined. It is believed that more than 90% of cases in the past were very rare. With the advent of videotapes to evaluate family members, lineages were analyzed. These studies show corneal changes corresponding to keratoconus in some members of the family, suggesting a hereditary autonomic pattern.
Keratoconus is associated with a wide variety of systemic and ocular conditions.
- Systemic partnerships: Atopy (a genetic predisposition to develop an allergic reaction): one of the most common appendages of keratoconus is atopy and appears in a condition similar to spring keratoconjunctivitis. The eye massage seen in systemic atopy plays a role in the development of keratoconus.
- Down syndrome (trisomy 21): In Down syndrome (trisomy 21), the frequency of severe dropsy is high, perhaps due to eye massage and/or these patients are rarely treated with keratoplasty and their disease is allowed to progress further.
- Ehlers-Danlos syndrome
- Marfan syndrome
- Crowzone syndrome
- Apert syndrome
- Congenital amaurosis of labor
- Retinitis pigmentosa
- Retinopathy of prematurity
- Fuchs corneal endothelial dystrophy
- Posterior polymorphous dystrophy
Because the prevalence of keratoconus in the general population is high, some associations may coincide.
Studies suggest several contributing factors:
Enzyme abnormalities in the corneal epithelium: Enzymatic abnormalities in the expression of lysosomal enzymes (catalase and cathepsin) and decreased levels of resistance of proteolytic enzymes (metalloproteinases of the tissue inhibitory matrix).
Differentially expressed corneal epithelium: The corneal epithelium that differentiates (as controls) between keratoconus and myopia in both gene expression and protein expression.
Molecular defect: The abnormal absence of the water channel protein aquaporin 5 in keratoconus compared to the normal corneal epithelium.
Gelatinolytic action: Gelatinolytic activity is described in the stroma, which may be due to decreased activity of enzyme inhibitors.
Corneal collagen and crosslinking abnormalities: Corneal collagen and crosslinking abnormalities can cause keratoconus.
Eye massage: Cytokine has been suggested as a mediator for eye massage and stromal thinning. In patients with atopic dermatitis, Down syndrome, and congenital photoreceptor depletion, congenital amaurosis of labor, keratoconus may be associated with forced eye massage or oculopharyngeal reflex. The latter is a pattern of behavior observed in children with visual and mental disabilities.
Pathophysiology: All layers of the cornea are believed to be affected by keratoconus, although corneal stroma thinning, Bowman’s membrane rupture, and iron deposition in basal epithelial cells, forming a fissure ring. The folds and tears in the membrane of the descent cause strong hydrops and stripes, which produce diffuse spots of varying amounts.
Risk factors for keratoconus
Risk factors for keratoconus include:
Particular risk factors include a history of atopic disease, especially eye allergies, contact lens wear, and intense eye massage. Most keratoconus cases appear abrupt, but some show evidence of genetic transmission.
Symptoms of keratoconus
Symptoms are highly variable and depend on the stage of the disease. Symptoms may be absent early in the disease. In advanced disease, there is a significant decrease and distortion of vision.
- Monocular polyopia (perception of multiple “ghost” images in the eye)
- Blurry vision
- Decreased visual acuity
- Progressive poor vision, not corrected with glasses
- Visual perception is impaired
- Contrast sensitivity decreased
- Increasing and burning the distortion around the light sources
- Recognized anisometropia (vision difference in both eyes)
- Photophobia (increased sensitivity to light)
- Istrian read clearly
- The night vision is low
- Monocular polyopia (perception of multiple “ghost” images in the eye), decreased visual acuity, and decreased contrast sensitivity can be seen in other disorders, especially early nuclear sclerotic cataracts.
To diagnose keratoconus, your ophthalmologist (ophthalmologist or optometrist) will review your medical and family history and perform an eye exam. He or she may perform other tests to determine more details about the shape of your cornea. Tests to diagnose keratoconus include:
Refraction of the eye: In this test, your ophthalmologist uses special devices that measure your eyes to detect vision problems. They may ask you to look through a device that has different lens wheels (phoropters), which can help determine which combination gives you clear vision. Some doctors may use a handheld retinoscope to evaluate your eyes.
Slit-lamp test: In this test, your doctor will direct a vertical beam of light onto the surface of your eye and use a low-power microscope to view your eye. He or she will evaluate the shape of your cornea and look for other potential problems with your eye.
Keratometry: In this test, your ophthalmologist will focus the circle of light on your cornea and measure the reflex to determine the basic shape of your cornea.
Computerized corneal mapping: Specialized photographic tests, such as corneal topography and corneal topography, record images to create a detailed map of the shape of your cornea. The corneal scan can also measure the thickness of your cornea. Corneal topography can often detect early signs of keratoconus before the disease is detected by a wedge lamp test.
Treatment for keratoconus
Treatment of keratoconus depends on the stage and severity of the condition. In the early stages, the symptoms are very mild and can be cured for many years.
Placement on the eyelid is the main treatment for keratoconus. In later stages, keratoconus causes very blurred vision and hypersensitivity to light. Treatment for this condition is as follows:
After glasses, lenses are considered a good option for keratoconus. Different types of lenses are used for the keratoconus, including:
Soft contact lenses
Soft contact lenses (similar to glasses) are used to correct blurred or distorted vision in the early stages of keratoconus. As the condition worsens, the cornea changes shape frequently over a short period of time, often resulting in a change in the concentration (prescription) of glasses or contact lenses.
Hard contact lenses
Hard contact lenses are also known as gas permeable or gas permeable contact lenses (GP or RGP lenses). Hard lenses can be uncomfortable to wear at first, but most patients adjust them after a while. These provide excellent vision and are more permeable to oxygen than soft lenses.
Gas permeable contact lenses (GPCL) are made from materials that contain silicone and fluorine and other additives.
If wearing contact lenses is uncomfortable, a combination of two different types of contact lenses can be worn on the affected eye.
The lenses are called piggyback and piggybacking lenses. The soft lens acts as a cushion for the hard lens, also known as “piggybacking.”
A lens is made of a soft material like silicone hydrogel. The other lens is the RGP lens placed on top.
Hybrid contact lenses have a focal point around the outer soft ring for comfort. Hybrid lenses are preferred for convenience over hard lenses.
Scleral lenses are useful for very irregular changes in the shape of the cornea during the early stage of keratoconus.
Scleral lenses have large diameters that sit on the sclera (the white part of the eye) creating an arch in the cornea. This provides stability, better vision, and comfort to the patient.
Eyeglass correction: initially, an attempt should be made to correct myopic astigmatism by suggesting a visual correction. Patients with early keratoconus receive satisfactory vision with the eyelid. The development of irregular astigmatism often limits the use of correction glasses and patients may need contact lenses.
Optical Gas Permeable (RGP) Contact Lenses: Optical gas permeable (RGP) contact lenses are often the first lens of choice and may be indicated after glasses-corrected sharpness is inadequate. Other lenses used are piggyback lenses, pure hydrogel lenses, multi-curve, or aspherical contact lenses. Wearing contact lenses often leads to intolerance, allergic reactions (eg, giant papillary conjunctivitis), corneal friction, neovascularization, and sometimes intolerance. Although contact lenses are very helpful, they increase the risk of corneal scarring.
Surgical treatment can be used when the patient does not improve with the use of contact lenses.
Contact lenses can fail due to:
- Inadequate sharpness
- The tolerance of the lens is not enough
- Frequent lens shifts
- Peripheral thinning
Keratoplasty: The standard surgical treatment consists of keratoplasty. Recurrence of keratoconus after keratoplasty is very rare. Recurrence may be due to:
- Incomplete excision of the cone during surgery
- Keratoconus not detected in the corneal donor
- Cellular activity of the host that causes changes in the donor’s corneal material
Lamellar Keratoplasty: Lamellar keratoplasty is effective but is not preferred due to the technical difficulties and reduced visual acuity of the procedure.
Epikeratoplasty: Epikeratoplasty was also successful, but was abandoned due to the visual outcome of the caption.
Keratoplasty Penetration: Keratoplasty penetration is very common. During keratoplasty, reducing donor-recipient size disparities reduces myopia after keratoplasty. Problems related to keratoplasty include corneal graft rejection, glaucoma, cataract formation, anisometropia, astigmatism, and infection.
Deep anterior laminar keratoplasty (DALK): Deep anterior laminar keratoplasty (DALK) has been proposed as an alternative to penetration in keratoplasty. Recent advances in surgical procedures have sparked interest in DALK. Basic benefits:
- Greater structural integrity
- Reduction of the risk of graft rejection
Although the presentation is challenging, innovative techniques such as the large bubble technique reduce surgical handling time, improve the safety of the procedure, and provide a visual result that allows penetration of the keratoplasty. DALK problems include graft-host interface fog, Descemet’s membrane perforations, and stromal rejection.
Intracorneal ring sections: Intracorneal ring sections have had some success in reducing myopia and astigmatism and improving visual acuity with visual correction in patients without corneal scars. INTACS (Addition Technology, Fermont, CA) are intrastromal corneal ring segments that are placed on the peripheral cornea mechanically or with a femtosecond laser.
Combined cross-linking of collagen riboflavin-ultraviolet rays type A (UVA): Combined crosslinking of collagen riboflavin-ultraviolet rays type A (UVA) by photosynthesis of vitamin B2 (photosensitizing substance) with UVA. This process increases the viscosity of the corneal collagen and therefore reduces the likelihood of further ectasis.