الفهرس 
Introduction & Aim of the WorkOnly 14 pages are availabe for public view
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Abstract
Keratoconus is a degenerative, non-inflammatory disorder of the cornea, characterized by central and para-central thinning and subsequent ectasia. This distortion of the corneal shape, results in irregular astigmatism with associated reduction in vision. It typically presents in adolescence and progresses in a variable manner.
Keratoconus is a little-understood disease with an uncertain cause, and its progression following diagnosis is unpredictable..
Several methods of measuring the corneal shape have been used. Corneal topography represents a significant advance in the measurement of corneal curvature over keratometry. Topography provides both a qualitative and quantitative evaluation of corneal curvature.
New technologies have met the demand for increased precision in evaluation of complex corneal shapes. These include Placido disk imaging, three dimensional topography, slit-scanning topography, Scheimpflug imaging, ultrasound, and corneal hysteresis.
The management of keratoconus varies depending on the state of progression of the disease. In early cases, spectacles and contact lenses may provide adequate visual correction.
Unfortunately, they are not the solution in all cases.
Discomfort and patient preference may limit the use of contact lens wear and in advanced cases fitting may be problematic. Severe ectasia and central corneal scarring in advanced keratoconus can significantly limit the amount of visual rehabilitation achieved by contact lenses.
For these reasons, between 10-25% of patients with keratoconus progress to a point where surgical intervention is required. Surgical options include: Intra-corneal ring segment insert (Intacs and Ferrara Rings), Riboflavin / Ultraviolet-A corneal cross linkage (CXL) and Corneal transplantation (or grafting) including penetrating keratoplasty and Lamellar keratoplasty.
The development of intra-corneal ring segments has provided a surgical alternative to corneal transplantation in some eyes with keratoconus. These ring segments have been used to reduce the irregularity of the cornea and flatten the apex of the cone in mild and moderate cases of keratoconus with some reported success.
Intacs are inserted into the posterior stroma. The circular intra-lamellar pockets for the rings are created either using a specially designed vacuum lamellar dissector or with the femtosecond laser. Intacs are the treatment of choice in the contact lens intolerant eye, with keratometry less than 53 diopters and no central corneal scarring and should be attempted before considering DALK (Deep anterior lameller keratoplasty).
It must be stressed, that intra-corneal ring technology does not offer a cure for the condition but can very often produce a marked improvement in unaided and best corrected visual acuity and allow eyes to be corrected with spectacles and / or soft rather than rigid lenses.
Corneal collagen cross-linkage (CXL) using Riboflavin/ ultraviolet–A light is a new therapeutic modality which may be the first available treatment to halt and stabilise the keratoconic process. Its aims are to increase the biomechanical stability of the corneal stroma, in terms of its tensile strength and its resistance to enzymatic digestion, by inducing and increasing cross-linkages between the stromal collagen fibres. The ability to halt disease progression at the earliest stages of the condition, when full visual rehabilitation can still be achieved with spectacles and soft contact lenses, offers great hope for future generations.
DALK negates the risk of endothelial rejection, improves postoperative biomechanical corneal stability and should reduce the risk of postoperative complications associated with intraocular surgeries. Many techniques are used to separate the stroma from Descemet’s membrane in lamellar keratoplasty including corneal injection with air, saline to turn the stroma opaque and so can be easily differentiated from Descemet’s membrane.
Further refinements in operative techniques, together with improvements in technologies, such as the implementation of femtosecond lasers and mechanical microkeratomes for DALK, will allow refinement of lamellar techniques and improve the ease of performing these procedures for both surgeons and patients alike.
Corneal transplant (penetrating keratoplasty) is one of the surgical options for keratoconus patients who cannot tolerate contact lenses or are not adequately visually rehabilitated by them. Central scarring may preclude good vision from contact lenses, even when they are tolerated.
The outcomes of PK for keratoconus are generally good, but when compared with the outcome of lamellar keratoplasty, the later DALK appears to cause less astigmatism and also has the advantage of no endothelial graft rejection..