Corneal Blindness is second most prevalent cause of blindness in world more so in developing country like India . Corneal transplantation for corneal pathologies has a long history ,and has enjoyed a relatively high success rate as compared with transplantation of other tissues.
What is cornea ?
Cornea is the transparent , dome shaped window covering the front of eye . Because there are no blood vessels on the cornea ,it is normally clear and has a shiny surface .
Layers of cornea :
- CORNEAL EPITHELIUM
- BOWMAN’S LAYER
- CORNEAL STROMA
- DESCEMENT’S MEMBRANE
- CORNEAL ENDOTHELIUM
If cornea becomes distorted in shape , scarred or hazy ( opaque) from disease or injury the light rays passing through it are distorted and vision is reduced .A corneal graft ( transplant) may be necessary to replace the diseased or injured cornea with a healthy clear cornea to restore good vision.
This operation is known as keratoplasty – replacement of part or all of your cornea with human donor tissue.
TYPES OF CORNEAL GRAFTING
- FULL THICKNESS ( PENETRATING GRAFTS ) when whole of cornea needs replacement.
- PARTIAL THICKNESS GRAFT replacing front of cornea (DALK / ALK ) to treat superficial damage to cornea.
- PARTIAL THICKNESS GRAFTS replacing back of cornea ( ENDOTHELIAL LAMELLAR ) used to treat conditions affecting only innermost cornea or endothelium
In penetrating keratoplasty , a circular button shaped , full thickness section of tissue is removed from diseased – cornea using either trephine or a femtosecond laser .
A matching ‘’button’’ from a donor tissue is then positioned and sutured into place.
Corneal transplantation generally takes 30-45 min meaning you can go home a short while after surgery ( though you will need someone to drive you home).
Because of cornea’s lack of bloody supply , healing takes place very slowly . restoration of vision after corneal transplant surgery is gradual . the vision in operated eye will be somewhat blurred and distorted until final glasses or contact lens are advised . this is sight saving surgery but it also requires patients and ophthalmologists to work closely together to insure the success of surgery .
There is a possibility that body will reject the graft . This is like an allergic reaction and can occur anytime after the surgery and can be treated successfully if you act immediately.
There are 4 danger signs one must know –
R – Redness
S – Sensitivity to light
V – Decreased vision
P – Pain
Anterior lamellar keratoplasty (ALK) Deep lamellar keratoplasty (DALK)
Anterior lamellar keratoplasty (ALK)
In ALK , we dissects the cornea into 2 thin pieces and removes the front scarred part . A matching area of healthy tissue from a donor . Cornea is then used to replace the area that was removed .
DEEP ANTERIOR LAMELLAR KERATOPLASTY (DALK)
It’s a type of ALK in which surgeon leaves behind only 5% or lens of original corneal thickness and replaces the rest with donor tissue . DALK surgery can be done with manual or hand dissection of donor tissue . it can also be done by using air called ‘ big bubble ‘ technique .
DALK is our treatment of choice for keratoconnus or corneal scares as long as the inner cell layer of the cornea ( endothelium) is healthy .
Advantages of anterior lamellar over penetrating keratoplasty :
- ALK/DALK is an extraocular procedure that offers intraoperative safety .
- There are fewer intraoperative/post operative complications than penetrating keratoplasty .
- Chances of graft rejection will be much less.
ENDOTHELIAL KERATOPLASTY :
Endothelial keratoplasty is the preferred way to restore vision when inner cell layer of cornea steps working properly like in Fuch’s dystrophy, bullous keratopathy ,ICE syndrome or other endothelial disorders .
In endothelial keratoplasty , the surgeon removes the diseased inner cell layer of the cornea and implants healthy donor tissue through a small incision . An air bubble is used to unfold and position the donor tissue against patient’s cornea .
DSEK : Descemet’s stripping with endothelial keratoplasty
Most common type of endothelial keratoplasty procedure is known as DSEK or DSAEK .
In this procedure ,the surgeon implants the back 20-30% of the donor cornea into patient’s eye .
DMEK: Descmet membrane endothelial kerstoplasty
This is more advanced technique of endothelial keratoplasty. The DMEK graft consist only of an isolated endothelium Descemet membrane layer. There use extremely thin donor tissue and provide more patients with 20/20 or 20/25 vision than DSEK or DSAEK .
Advantages of endothelial keratoplasty over penetrating keratoplasty .
- Less operating time and faster recovery .
- Mimimal removal of corneal tissue and therefore less impact on the structural integrity of eye.
- No suture related complications .
- Reduced risk of astigmatism after surgery .