CORNEAL REFRACTIVE SURGERY

Corneal Physiology

Transparent, dome shaped, outermost layer that covers the front of the eye.

Provides greatest amount refractive power to the eye. Avascular, relies on atmosphere for oxygen and aqueous humor

for its nutritional needs. Corneal surface is kept smooth by

constant moistening action of tears.

Layers of CorneaEpithelium (55µm). It evenly distributes the nutrients to other layers. It maintains stromal dehydration.

Stroma (470µm) Collagen fibers arrangement are responsible

for corneal strength, optical characters.

Endothelium (5µm). It stretches to cover the dead cells,

which reduces the cell density and impact

on fluid regulation. It pumps the excess fluid from stroma.

Shape of Cornea Slightly oval Horizontal & vertical dimensions are 11mm & 12 mm app. Pupil diameter ranges from 2mm to 6mm, which reduces optical

zone of cornea to its central 6mm. Peripheral cornea is thicker than central cornea.

Pachymetry It is the process of measuring the thickness of the cornea. Corneal Pachymetry is essential prior to a LASIK procedure for

ensuring sufficient corneal thickness to prevent abnormal bulging of the cornea, a side effect known as ectasia.

Ultrasonic & Optical pachymetry. It also helps in finding the development of glaucoma when

combined with standard measurement of IOP. Corneal thickness is 560 microns.

Corneal Topography It is a process of mapping the surface curvature of the

cornea. It is to produce a detailed description of the shape

and power of the cornea because shape determines the visual ability.

Refractive Laser Surgery

LASIK

Advantages: Pain free recovery. Quick restoration of eyesight. Better result for severe

short sight.

Disadvantages: Dry eyes. Halos, starburst. Loss of contrast sensitivity. Thick corneal flap (100-180 microns).

Femto LASIK

Photorefractive Keratectomy

Used to correct mild to moderate Myopia. Hyperopia. Astigmatism.

Advantages: Highly accurate for myopia. 80% patients have 20/20 vision

Disadvantages: Mild discomfort including minor

eye irritation. Dry eyes.

LASEKAdvantages: No flap complications. Causes less dry eyes than

LASIK. Finer trephine blade is used

instead of microkeratome. Good for patient with

thin cornea.

Disadvantages: May cause more pain and

discomfort than LASIK. Dry eyes. Longer recovery time than

LASIK.

Epi-LasikAdvantages: Less complications to corneal nerves.Disadvantages: Dry eyes. Poor night vision.

Intrastromal Corneal Implants

Used to treat Myopia. Keratoconus. It has two semicircular rings made of PMMA.

Advantages: Easily removable. Small incision.

Disadvantages: Vision disorder. Problem with night vision.

Thank You

Prepared byGhose MohamedMedicals International RiyadhKSA