2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. Refractive Laser Surgery
8. 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).
9. Femto LASIK
10. 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.
11. 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.
12. Epi-LasikAdvantages: Less complications to corneal nerves.Disadvantages: Dry eyes. Poor night vision.
13. 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.