الفهرس 
IntroductionOnly 14 pages are availabe for public view
Abstract
Keratoconus is a common disorder (prevalence of about 50 per 100,000) in which the central or paracentral cornea undergoes progressive thinning and bulging, so the cornea takes the shape of a cone.
Nearly all cases are bilateral, but oneeye may be much more severely involved. Sometimes the less affected eye shows only high astigmatism, which may be considered the minimal manifestation of keratoconus. (McMonnies CW, 2007).
Tears in Bowman layer and the adjacent underlying corneal stroma result in opaque superficial corneal scars .A progressive visual impairment follows the irregular myopic astigmatism and sometimes opacification of the cone. (Klintworth,2008).
Surgery for keratoconus is indicated when the patient is unable to obtain clear, comfortable vision without too much glare with contact lenses or if contact lenses cannot be comfortably worn most of the day. (Maguire, 1998).
In penetrating keratoplasty (PK), full thickness host corneal tissue is replaced with full thickness donor corneal tissue. The surgeon must be prepared to deal with postoperative complications. Some of the more common complications include wound leaks, epithelial defects, increased IOP, and difficult to control postoperative inflammation. (Skeens and Holland, 2010).
Since all three layers of the cornea allograft can undergo rejection independent of each other, corneal graft rejection can be classified. Panda et al. classified cornea graft rejection based on a review of the literature, into epithelial, stromal and endothelial rejection. (Skeensand Holland, 2010).
Endothelial rejection is the most important aspect of corneal graft rejection because of the crucial physiological role played by this layer of cells.
Rejection and the consequent destruction of the corneal endothelium result in the entire graft becoming edematous, vascularized, and inflamed, whereas rejection of the stroma or epithelium can be transient and inconsequential. (Klintworth, 2008).
In the past few years, deep anterior lamellar keratoplasty (DALK) has seen renewed interest as an alternative to conventional penetrating keratoplasty.
The introduction of several new dissection techniques, the optical visualization of dissection depth during surgery, and the availability of various lasers may provide new possibilities for the management of anterior corneal disorders.
In fact, we may be currently witnessing the most dramatic change in the concept of keratoplasty from being a conventional penetrating procedure towards that of custom-made corneal tissue replacements. (Gerrit R.J. Melles, 2006).
For nearly half a century, penetrating keratoplasty (PKP) has been the surgical treatment of choice for visual re-habilitation of keratoconus (KC). Recently, deep anterior lamellar keratoplasty (DALK) has been introduced as an alternative to PKP.
This procedure offers the inherent advantages of elimination of immune-mediated endothelial rejection and complications associated with its prevention and treatment, such as steroid-induced glaucoma and cataracts, as well as elimination of complications unique to intraocular procedures, such as expulsive hemorrhage, endophthalmitis, and architectural disturbances of the anterior chamber. (Cohen et al, 2010).
Keratoconus is a common disorder (prevalence of about 50 per 100,000) in which the central or paracentral cornea undergoes progressive thinning and bulging, so the cornea takes the shape of a cone.
Nearly all cases are bilateral, but oneeye may be much more severely involved. Sometimes the less affected eye shows only high astigmatism, which may be considered the minimal manifestation of keratoconus. (McMonnies CW, 2007).
Tears in Bowman layer and the adjacent underlying corneal stroma result in opaque superficial corneal scars .A progressive visual impairment follows the irregular myopic astigmatism and sometimes opacification of the cone. (Klintworth,2008).
Surgery for keratoconus is indicated when the patient is unable to obtain clear, comfortable vision without too much glare with contact lenses or if contact lenses cannot be comfortably worn most of the day. (Maguire, 1998).
In penetrating keratoplasty (PK), full thickness host corneal tissue is replaced with full thickness donor corneal tissue. The surgeon must be prepared to deal with postoperative complications. Some of the more common complications include wound leaks, epithelial defects, increased IOP, and difficult to control postoperative inflammation. (Skeens and Holland, 2010).
Since all three layers of the cornea allograft can undergo rejection independent of each other, corneal graft rejection can be classified. Panda et al. classified cornea graft rejection based on a review of the literature, into epithelial, stromal and endothelial rejection. (Skeensand Holland, 2010).
Endothelial rejection is the most important aspect of corneal graft rejection because of the crucial physiological role played by this layer of cells.
Rejection and the consequent destruction of the corneal endothelium result in the entire graft becoming edematous, vascularized, and inflamed, whereas rejection of the stroma or epithelium can be transient and inconsequential. (Klintworth, 2008).
In the past few years, deep anterior lamellar keratoplasty (DALK) has seen renewed interest as an alternative to conventional penetrating keratoplasty.
The introduction of several new dissection techniques, the optical visualization of dissection depth during surgery, and the availability of various lasers may provide new possibilities for the management of anterior corneal disorders.
In fact, we may be currently witnessing the most dramatic change in the concept of keratoplasty from being a conventional penetrating procedure towards that of custom-made corneal tissue replacements. (Gerrit R.J. Melles, 2006).
For nearly half a century, penetrating keratoplasty (PKP) has been the surgical treatment of choice for visual re-habilitation of keratoconus (KC). Recently, deep anterior lamellar keratoplasty (DALK) has been introduced as an alternative to PKP.
This procedure offers the inherent advantages of elimination of immune-mediated endothelial rejection and complications associated with its prevention and treatment, such as steroid-induced glaucoma and cataracts, as well as elimination of complications unique to intraocular procedures, such as expulsive hemorrhage, endophthalmitis, and architectural disturbances of the anterior chamber. (Cohen et al, 2010).