Patient Education
Introduction
The cornea is the transparent round watch glass-like structure that forms the central anterior part of the outer tunic of the eyeball, surrounded by the non-transparent white sclera. The cornea has a convex curvature which is slightly steeper in the center than the periphery.
Corneal ectasias are disorders in which there is an abnormal protrusion of the corneal tissue, usually associated with corneal thinning. Keratoconus is the most common corneal ectasia in which there is a central or inferior cone-shaped forward protrusion of the cornea associated with thinning. It is a progressive disorder, most commonly occurring in the 2nd and 3rd decades of life.
However, there is an increasing incidence of this disease in recent years, along with a drastic shift in the age of diagnosis towards younger ages, of even 8 to 10 years.
Keratoconus leads to a decline in vision due to distortion of the normal image formed on the retina, as a result of several refractive aberrations due to the altered corneal curvature. In children, this can even lead to an irreversible decline in vision due to induction of amblyopia, if not identified and treated in time. Advanced cases can lead to severe corneal thinning and scarring, with eventual rupture in the Descemet’s membrane of the cornea leading to sudden imbibition of fluid in the cornea and severe loss of vision, a phenomenon called hydrops, which leads to permanent corneal scarring.
Causes
Multiple predisposing factors for keratoconus have been identified for this disorder. The most common ones include:
- Chronic eye rubbing - This is commonly seen in children with allergic conjunctivitis. The long-term habit of rubbing the eyes due to itching, along with inflammatory mediators released due to the allergy leads to gradual progressive steepening of the corneal curvature and results in keratoconus. Hence, allergic conjunctivitis demands timely treatment to prevent such sequelae.
Dry eyes can also instigate eye rubbing habits along with chronic ocular surface inflammation and predispose to keratoconus. Increasing screen time in children and young adults has led to a sharp rise in the incidence of this phenomenon in this age group, correlating with the rising incidence of keratoconus in them.
- Genetic – Keratoconus often runs in families and many patients have a genetic predisposition. It is imperative for siblings and offspring of patients with keratoconus to get routinely screened by ophthalmologists.
- Hormonal – Patients with hormonal fluctuations, as seen in polycystic ovary syndrome (PCOS), thyroid disorders, pregnancy, and lactation can predispose to keratoconus due to a change in the consistency and biomechanical weakening of the corneal tissue. Adolescent girls with PCOS must be advised routine eye check-ups to ensure early diagnosis.
- Systemic syndromes – Patients with Down’s syndrome, Marfan’s syndrome, and other connective tissue disorders are at a higher risk of developing this corneal ectasia.
- Vitamin D deficiency – Lower vitamin D levels have been associated with the weakening of the corneal tissue. This is another rising trend seen due to increasing indoor activities and lack of sunlight exposure, especially since the COVID pandemic. Children must be encouraged to go outdoors, and minimize indoor activities, especially screen time, for the same.
- Sleeping with face down – The habit of sleeping with the face down towards the pillow is seen to have a compressive effect similar to eye rubbing and has been associated with a higher risk for keratoconus.
Symptoms
Patients often present with progressive diminution of vision, usually associated with glare or halos around light. Children are often diagnosed due to difficulty in seeing distant objects like the teaching board in school or when parents or teachers notice squinting or narrowing of the eyes while trying to focus on distant objects. There is often a history of repeated frequent changes in the spectacle prescription with vision not being fully clear even with glasses.
Diagnosis
It is done by examining the vision, refraction, slit-lamp examination, and tomography (3-dimensional study of the corneal curvature). Corneal imaging with tomography is a sensitive diagnostic technique, which helps to identify early sub-clinical cases and to study disease progression or stability after treatment.
Treatment
Keratoconus is an irreversible disorder. Treatment aims to stabilize the disease to stop further progression and decline in vision, or in advanced cases, to replace the corneal tissue with a healthy one. Subsequently, visual rehabilitation can be planned using various aids.
The most common treatment for progressive mild to moderate keratoconus is corneal collagen cross-linking. It is a minimally invasive procedure under local anesthesia that involves the instillation of Riboflavin drops in the eye, followed by exposure to ultraviolet light. This induces cross-linking between collagen molecules in the cornea, leading to the strengthening of the tissue and arrest in further steepening and thinning.
Some patients may benefit from the implantation of ring segments in the cornea which help to flatten the ectatic cornea and improve visual status. The procedure is combined with cross-linking.
Patients with advanced keratoconus require a partial or full-thickness corneal transplant. The procedure is usually performed in children under general anesthesia and requires greater post-operative care and long-term follow-up in order to ensure wound healing, screen for graft infection, and for suture removal. Post corneal transplant, patients have to be maintained on long-term steroid eye drops to prevent graft rejection. However, in children, these may lead to a higher risk of secondary glaucoma. Hence routine follow-ups are mandatory to measure the intraocular pressure and examine the optic nerve for early signs of disease. Any sudden onset redness, watering, pain or blurring, or vision following transplant must be immediately reported to the ophthalmologist in order to identify graft rejection and institute prompt treatment for the same.
Patients with keratoconus must be strictly advised to avoid eye rubbing and trauma in order to minimize the risk of hydrops. Patients with keratoconus are strictly contraindicated from undergoing laser refractive surgeries in the future for correction of refractive errors as these lead to further thinning of the cornea.
Visual rehabilitation in these patients can be done using spectacles in cases with smaller refractive errors, or contact lenses. Special contact lenses like a corneoscleral lens, rigid gas permeable lens, Rose-K lens, and hybrid lens have been developed to fit the irregular corneal curvature and neutralize it to provide a smooth curvature.
Patients require a regular follow-up at 3-6 month intervals in order to monitor disease progression, mainly using topography and to assess the refractive changes. Contact lens fitting must also be regularly assessed subsequently, once disease stabilization is achieved.
Adjuvant treatment:
Associated conditions like allergic conjunctivitis, vitamin D deficiency, and hormonal imbalance must be corrected simultaneously in order to prevent further aggravation of the disease.
Conclusion
Keratoconus is an increasingly common ocular disorder in young adolescents and can lead to significant visual disability in this age group. If unidentified in younger children, it can lead to permanent visual loss due to amblyopia. With the rising trends of high screen time and changing lifestyles, children are at a higher risk of this disease. These mandates appropriate lifestyle modification in order to prevent this disease, along with routine screening for early diagnosis and prompt management.