What Is Keratoconus?

Overview

Keratoconus is a condition affecting the eye where the cornea becomes thinner and starts to bulge. This causes the cornea to take on a cone-like shape instead of its normal dome shape. 

Keratoconus typically starts during adolescence (around the time of puberty) or early adulthood and gradually progresses over time. The exact cause of keratoconus is unknown, but it’s believed to involve both genetic and environmental factors. 

Common symptoms of keratoconus include frequent changes in eyeglasses or contact lens prescriptions, increased sensitivity to light and glare, and blurred or distorted vision. Diagnosis involves a comprehensive eye examination, including tests that assess corneal shape and thickness. 

While there is no cure for keratoconus, there are treatment options available. During the initial phases, visual strength is corrected with eyeglasses or soft contact lenses. Hard oxygen-permeable (allows oxygen to pass through) contact lenses are often used as the condition progresses to provide better visual ability by creating a smoother corneal surface. For severe cases or when contact lenses are not well-tolerated, surgical treatment may be considered. Corneal collagen cross-linking (CXL) is a procedure that strengthens the cornea to stop the progression of the disease.

Regular follow-up visits with an optometrist or ophthalmologist are important for monitoring the condition and adjusting treatments as needed. Early detection and appropriate management can help minimise visual impairment and improve the overall quality of life for individuals with keratoconus.

Causes of keratoconus

While specific causes of keratoconus are unknown, a combination of genetic and environmental factors are considered to be responsible. Possible factors that could play a role in developing keratoconus include: 

• Genetic Predisposition: There is evidence suggesting a genetic component to keratoconus. It often runs in families, and certain genetic variations may increase the likelihood of developing the condition.
• Environmental Factors: Certain environmental factors can potentially contribute to the onset of keratoconus. These factors include the usage of contact lenses, repetitive eye rubbing, and the presence of hypersensitivity-related conditions such as hay fever (allergic rhinitis), sleep apnoea, eczema (atopic dermatitis) or allergic asthma.
• Enzyme Imbalance: Imbalances in enzymes that maintain the structure of the cornea's collagen may contribute to developing keratoconus. These imbalances can weaken the cornea and cause its irregular shape.
• Other underlying causes: Keratoconus may co-occur in disorders such as Down syndrome, Leber congenital amaurosis, Ehlers-Danlos syndrome, Marfan syndrome, or brittle cornea syndrome.

It's important to note that while these factors are associated with keratoconus, the condition can still occur without any identifiable cause.^1,2 

Signs and symptoms of keratoconus

Keratoconus can manifest through various signs and symptoms, indicating the presence of the condition. These signs and symptoms may include:

• Blurred or distorted vision:  Vision may become mildly blurred or progressively deteriorate over time. Objects may appear distorted or skewed, making it challenging to focus on them.
• Increased sensitivity to light and glare: This can lead to discomfort and difficulties in situations with high light intensity, such as during sunny days or when facing direct light sources.
• Poor night vision: Difficulty seeing clearly at night.
• Distorted or multiple images (ghosting): Some individuals may encounter double vision (diplopia), or see a partial, incomplete image surrounding what they are focusing on (referred to as 'ghost' images). This effect, known as ghosting, occurs when light entering the eye is not properly focused due to the irregular shape of the cornea.
• Visual acuity: Decline in sharpness of vision.
• Eye irritation and eye rubbing: Keratoconus can cause eye irritation, redness, and itchiness. The constant rubbing of the eyes, either due to discomfort or habit, is often observed in individuals with keratoconus.
• Corneal hydrops: In advanced cases of keratoconus, the cornea can develop sudden swelling and become significantly thinner. This condition is known as corneal hydrops and can cause sudden vision deterioration and increased sensitivity to pain.
• Irregular astigmatism: It refers to an irregular curvature of the eye.

It is important to note that these signs and symptoms can vary in severity between individuals and may progress differently over time. 

If you are experiencing any of these symptoms or suspect you may have keratoconus, it is recommended to consult an eye care professional for a comprehensive examination and diagnosis.^1,3 

Management and treatment for keratoconus

The management and treatment of keratoconus depend on the severity of the condition and the individual's specific needs. Here are some common approaches used in the management of keratoconus:

1. Eyeglasses or contact lenses: In the early stages of keratoconus, eyeglasses or soft contact lenses can help correct vision by compensating for the irregular shape of the cornea.  However, as the condition progresses, patients typically need to transition to wearing specially designed hard contact lenses, such as rigid gas permeable (RGP) lenses or scleral lenses, which may be prescribed to provide better vision and comfort.
2. Corneal cross-linking (CXL): It involves applying riboflavin (vitamin B2) eye drops followed by exposure to ultraviolet (UV) light. This treatment aims to strengthen the cornea by creating new cross-links within its collagen fibres. Corneal cross-linking can help slow down the progression of keratoconus, stabilise the cornea and, in some cases, even improve vision.
3. Intrastromal corneal ring segments (ICRS): ICRS, also known as corneal implants or corneal rings, are small plastic rings that are surgically inserted into the cornea to reshape it. This procedure helps improve vision by reducing corneal irregularities associated with keratoconus. The procedure typically lasts around 15 minutes.
4. Keratoplasty (corneal transplantation): In severe cases of keratoconus, where other treatments are not effective, corneal transplantation may be considered. This surgical procedure involves replacing the damaged cornea with a healthy donor cornea. Different types of corneal transplantation techniques, such as penetrating keratoplasty (PK) or deep anterior lamellar keratoplasty (DALK), may be utilised depending on the parts of the cornea that need replacing. In most cases, glasses or contact lenses are still needed to achieve the clearest vision following the transplant surgery.^3,4

Diagnosis of keratoconus

The diagnosis of keratoconus involves a combination of clinical examination and specialised tests. Ophthalmologists commonly use the following methods to diagnose keratoconus:

1. Slit-lamp biomicroscopy: Allows the ophthalmologist to observe any corneal damage such as thinning, scarring, and irregularities by examining the cornea closely.
2. Corneal topography: This non-invasive imaging technique creates a detailed map of the corneal surface. It measures the curvature and shape of the cornea, helping to identify any characteristic irregularities associated with keratoconus.
3. Pachymetry: It assesses corneal thickness, with thinning commonly observed in the central area of the cornea.
4. Keratometry: Keratometry measures the cornea's curvature by focusing light on its surface. It helps determine if there is corneal steepening, which is a typical finding in keratoconus.
5. Refraction test: A refraction test determines the prescription needed to correct vision. In keratoconus, frequent changes in refractive error may occur, requiring adjustments to the prescription over time.

Ophthalmologists can accurately diagnose keratoconus by considering these diagnostic methods in conjunction with the patient's symptoms and medical history.^2,3,5,6 

Risk factors

These factors can elevate the likelihood of developing keratoconus:

1. Genetics: Family history of keratoconus.
2. Eye rubbing: Persistent and forceful eye rubbing.
3. Connective tissue disorders: Ehlers-Danlos syndrome, Marfan syndrome, osteogenesis imperfecta.
4. Allergies: Chronic and severe allergic eye disease.
5. Hormonal imbalances: During puberty. 
6. Eye trauma: Severe eye injuries.
7. Sleep apnea
8. Genetic conditions: Down syndrome ^2,3

Complications

Possible complications of keratoconus include

1. Acute corneal hydrops: In rare cases, advanced keratoconus can lead to acute corneal hydrops characterized by corneal swelling caused by breaks in Descemet's membrane.
2. Secondary corneal scarring: Keratoconus can result in corneal scarring, which can further impact vision and visual quality.⁷ 

FAQs

Can keratoconus be prevented?

There is no known way to prevent keratoconus currently. Taking preventative measures to protect your eyes (e.g., wearing sunglasses, not rubbing them, having regular check-ups, etc.) is always advised.

How common is keratoconus?

Keratoconus affects around 1 in 2,000 people on average.

When should I see a doctor?

If you are noticing changes in your vision, book an appointment to see your doctor right away. Early intervention is the best way to prevent further visual impairment.

Summary

Keratoconus is an eye condition where the cornea thins and bulges into a cone shape. Starting in adolescence, it progresses over time, causing blurred vision, light sensitivity, and altered night vision. Several genetic and environmental factors contribute to its development. Diagnosis involves comprehensive eye exams and tests. Treatments vary based on severity, including eyeglasses, contact lenses, corneal cross-linking to strengthen the cornea, and surgical options like corneal transplantation. Risk factors include genetics, eye rubbing, and certain conditions. Complications may include acute corneal hydrops and corneal scarring, emphasising the importance of early detection and appropriate management.