Keratoconus: Window and Scissor Reflexes in Cornea

KERATOCONUS- Cone Shaped Cornea

WHAT IS KERATOCONUS?

Keratoconus or Conical cornea is bulging out of normal round cornea into a cone-like structure due to ectasia (dilatation) and thinning of the cornea.

In this blog, we will focus on Window reflexes and Scissor reflexes in cornea occuring in Keratoconus. Keratoconus is usually bilateral, non-inflammatory and along axial part of cornea.

The disease starts around puberty and progresses slowly with further expansion of keratoconus.

TYPES OF KERATOCONUS

Depending upon shape and size, there can be 3 variations of keratoconus as:-

1. Nipple cone- <5mm with steep curvature
2. Oval cone- 5-6mm with ellipse
3. Globus cone- >6mm with round globe

PATHOGENESIS OF KERATOCONUS

Thinning and ectasia (dilation) is the major pathology which occurs due to defect in synthesis of mucopolysacchride and collagen tissue.

CLINICAL FEATURES OF KERATOCONUS

The patient presents with symptoms while a careful examination helps in assessing signs:-

SYMPTOMS

1. Myopia (short-sightedness)
2. Astigmatism

SIGNS

1. Slit lamp examination- reveals thinning and dilatation of central cornea.
2. Retinoscopy- Scissor reflex of Cornea in Keratoconus- Action of two bands moving toward and away from each other like the blades of a pair of scissors. It occurs with Astigmatism.
3. Distant direct ophthalmoscopy- oil droplet reflex is observed. (central and peripheral areas of cornea are separated by shadows)
4. Keratometry- abnormal mires alignment
5. Photokeratoscopy- distorted circles
6. Placido disc examination- irregular circles
7. Munsan's sign- patient lower lid bulges when he is asked to look down.
8. Window reflex of Cornea in Keratoconus- Also known as Blink or Corneal reflex, it is involuntary blinking of eyelids in response to stimuli. It is distorted in keratoconus.

ASSOCIATIONS OF KERATOCONUS

Keratoconus may be associated with ocular conditions or systemic conditions:-

• Ocular conditions- Ectopic lentis, congenial cataract, vernal keratoconjunctivits (VKC).
• Systemic conditions- Down syndrome, marfan syndrome, atopy, osteogenesis imperfecta.

COMPLICATIONS OF KERATOCONUS

The rupture of descemet's membrane can lead to acute hydrops, which with keratoconus, leads to corneal oedema, pain, vision loss, photophobia (light sensitivity) and lacrimation (excess tears).

TREATMENT OF KERATOCONUS

1. EARLY CASES

• Spectacles- for correction of vision
• Contact lenses- for correction of vision
• Intracorneal ring segments (Intacs)- for vision correction

2. TO SLOW DOWN DEGENERATION

Corneal collagen cross linking can be done:-

3. LATE CASES

Keratoplasty is the only viable option, namely DALK (Deep Anterior Lamellar Keratoplasty) or PK (Penetrating Keratoplasty).