الفهرس 
Acknowledgments
Aetiology and pathogenesis of keratoconusOnly 14 pages are availabe for public view
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Abstract
The progressive nature of keratoconus, which is due to continuation of the pathological processes within the corneal tissue, together with its bilaterality, have made it one of the disease that have a very high impact on the quality of life, either by the disease itself, or by the treatments that were available before CXL.
It is a relatively common disease with its annual incidence being one in 2000 and mostly with a multifactorial etiology. It usually affects patients at the adolescent age in the beginning of their productive life.
Before the advent of CXL, different modalities of treatment were targeting the visual complications of the disease, unlike CXL which targets the pathological basis of KC and halts its progression.
The aim of this study was to evaluate the effect of CXL as a treatment of KC through the evaluation of cessation of progression and evidence of regression of corneal ectasia.
The study evolved into a prospective comparative study that compared between the Epi-Off with the Epi-On techniques when the accelerated UVA protocol was used, and compared between the conventional and accelerated UVA protocols when the epithelium was left intact (Epi-On). So the treatment modalities in this study were divided into three techniques with their subgroups;
1. The Epi-Off / Accelerated UVA treatment (Subgroup 2):
In this technique, the corneal epithelium was removed in the central 8-9 mm, and then a specific riboflavin solution was instilled and spread over the cornea every two minutes for 30 minutes, and then the cornea was irradiated with UVA of wavelength of 370 nm, with a power of 10 mW/Cm2 for 9 minutes to deliver total energy of 5.4 J.
2. The Epi-On / Conventional UVA treatment (Subgroup3):
The corneal epithelium was left intact while a specific riboflavin was instilled over the cornea every two minutes for 30 minutes, then the cornea was irradiated with UVA of wavelength of 370 nm, with a power of 3 mW/Cm2 for 30 minutes to deliver total energy of 5.4 J.
3. The Epi-On / Accelerated UVA treatment (Subgroup 4):
The corneal epithelium was left intact while a specific riboflavin was instilled over the cornea every two minutes for 30 minutes, then the cornea was irradiated with UVA of wavelength of 370 nm, with a power of 10 mW/Cm2 for 9 minutes to deliver total energy of 5.4 J.
On comparing the effect of Epi-Off (Subgroup 2) and Epi-On (Subgroup 4) on the outcomes, using the accelerated UVA protocol, the Epi-Off technique (Subgroup 2) was found significantly better than the Epi-On technique (Subgroup 4) in most of the studied parameters specially at the 12-month visit. Epi-Off showed better outcomes in; UCVA, BCVA, MRSE, refractive cylinder, corneal astigmatism, K2, Km, Kmax, and Q-value. The rest of the studied parameters revealed non-significant difference between Epi-Off and Epi-On techniques, these parameters include; K1, (I-S), pachymetry at thinnest location, Y-coordinate, average thickness increase, front and back elevations. On the other hand, subgroup 2 resulted in significantly better success rate (90.6%) when compared to the success rate of subgroup 4 (62.5%).
On comparing the Conventional (Subgroup 3) and Accelerated (Subgroup 4) UVA treatment protocols within the Epi-On group, we found non-significant difference between the two groups in almost all of the studied parameters; UCVA, BCVA, corneal astigmatism, K2, Km, Kmax, (I-S), pachymetry at thinnest location, Y-coordinate, Q-value and average thickness increase. While subgroup 3 resulted in significantly better outcomes in MRSE, refractive cylinder, K1, front and back elevations. On the other hand, subgroup 3 resulted in significantly better success rate (81.8%) when compared to the success rate of subgroup 4 (62.5%).
Thus, both of subgroup 2 and subgroup 3 (90.6% and 81.8% respectively) give better results than subgroup 4 (62.5%), but with more significant results seen with subgroup 2. This means that removing the epithelium and using the conventional UVA protocol, both have resulted in better results, but it seems that, removing the epithelium is more significant for the success of CXL.
While in subgroup 2, it was a prerequisite to remove the epithelium at the central part of the cornea, in subgroup 3 and subgroup 4 it was a prerequisite not to remove the epithelium and leave it intact. So it is logical to find the complications related to epithelial trauma and healing (delayed healing and anterior stromal haze) almost exclusively in subgroup 2.
Recommendations:
1- Use the silicone ring container to keep riboflavin in contact with the cornea uniformly all the time and to protect the limbus during UVA irradiation.
2- Instill the riboflavin every 2 minutes both during the corneal saturation phase and the UVA irradiation phase.
3- Use the riboflavin solution that contains HPMC instead of dextran for both Epi-Off and transepithelial (Epi-On) techniques, as HPMC is, as viscous as dextran, without the stromal-thinning effect of dextran and without its inhibitory effect on riboflavin penetration.
4- Use the riboflavin solution that contains NaCl for the transepithelial (Epi-On) technique, as NaCl increases the riboflavin penetration through intact epithelium through enhancing the paracellular transport of riboflavin.
5- Increasing the total energy of UVA from 5.4 J to 7.2 J in Epi-On CXL may overcome the blocking effect of corneal epithelium.
6- Longer follow-up beyond the first postoperative year is recommended to find out the long term stabilization effect of these three techniques of CXL.Warnings:Avoid using 50% alcohol in debridement of corneal epithelium as it causes more keratocyte loss and more corneal oedema.Avoid using riboflavin solutions containing dextran as it has two major drawbacks, it results in intra-operative corneal thinning and inhibits the paracellular transport of riboflavin through the corneal epithelium.Avoid removing the lid speculum and allowing blinking during riboflavin instillation as it wipes the riboflavin off the cornea resulting in a decrease in stromal saturation.Avoid instillation of riboflavin in the conjunctival sac; it should be instilled on the corneal surface.