Introduction

Keratoconus is a common ophthalmological condition seen in practice, affecting around 1 in 450 people in the United Kingdom with a slight predominance in non-caucasians, although all races are affected1.

It causes a progressive thinning of the cornea which can cause visual disturbances including blurry vision, double vision, astigmatism and photosensitivity.

Physiology of the cornea

The cornea is the transparent and avascular structure covering the front of the eye. Despite its small diameter of approximately 12mm, it has essential structural and refractive properties as the cornea is thickest in the centre of the eye at around 0.5mm, becoming thinner further away from the centre. It is innervated by a branch of the first division of the ophthalmic nerve originating from the trigeminal nerve, called the nasociliary branch2.

Pathophysiology

In keratoconus, the cornea becomes progressively thinned and  occupies a more cone-like shape. The reason for this remains unclear although a mixture of genetic, hormonal and environmental factors are thought to be implicated1. It is a progressive disorder which is usually diagnosed in puberty and advances until middle age when progression slows or ceases1. Image 1 below shows the typical cone shaped cornea seen in keratoconus.

Keratoconus eye

Eye with keratoconus. Image from wikimedia commons. Author: William Charles Caccamise, Sr, MD

Problems associated with keratoconus1,4,5

  • Eye irritation
  • Blurred vision
  • Headaches
  • Sensitivity to light
  • Acute hydrops- rapid swelling of the cornea associated with loss of vision

Diagnosis

Slit lamp examination followed by corneal topography is performed using a digital camera to record the thickness of the cornea along its length3. This produces a digital map of the cornea4.

 

Corneal Topography

Corneal topography. Image from Wikimedia Commons. Author: Elise A. Slim et al.

Management

Keratoconus is progressive and non reversible5. Early management is crucial to prevent the further deterioration of the cornea. Generally, the quicker the management is initiated the less invasive it is. In early stages, spectacles and rigid contact lenses can be used to slow progression1.

Collagen cross linking uses ultraviolet A and riboflavin (vitamin b2) to prevent further degeneration of keratoconus. It aims to stiffen and strengthen the cornea to prevent the cornea from coning further6.

In severe cases, a corneal transplant from a deceased donor may be the only option to restore the refractive properties of the cornea and vision in patients. This happens in around 15-20% of patients4.

References

  1. NHS. Keratoconus.; 2014. Accessed August 22, 2017.
  2. DelMonte DW, Kim T. Anatomy and physiology of the cornea. J Cataract Refract Surg. 2011;37(3):588-598. doi:10.1016/j.jcrs.2010.12.037.
  3. How is keratoconus diagnosed? – Keratoconus NZ. Accessed August 22, 2017.
  4. NKCF. Keratoconus Symptoms | Blurred Vision | Light Sensitivity. Accessed August 22, 2017.
  5. Vaughan D, Asbury T. General Ophthalmology. 10th ed.; 1983.
  6. Randleman JB, Khandelwal SS, Hafezi F. Corneal cross-linking. Surv Ophthalmol. 2015;60(6):509-523. doi:10.1016/j.survophthal.2015.04.002.