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.
LASIKAdvantages: 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).
Photorefractive KeratectomyUsed to correct mild to moderate Myopia. Hyperopia. Astigmatism.Advantages: Highly accurate for myopia. 80% patients have 20/20 visionDisadvantages: 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 ImplantsUsed to treat Myopia. Keratoconus. It has two semicircular rings made of PMMA.Advantages: Easily removable. Small incision.Disadvantages: Vision disorder. Problem with night vision.