be achieved during the Þrst 6 months. Therefore, combining TG PRK with CxL in the same session leads (according to this opinion) to unpredictable results because unstable tissue is being treated in such a case.

The thesis behind the other idea (both in the same session) is: It is of nonsense to strengthen the cornea by CxL, then re-weaken it after 6 months by ablating part of the anterior corneal stiff tissue. Therefore, it is wise to ablate the diseased tissue and cross-link the remaining tissue.

To apply the above ideas, let us take an example: A patient has a progressive KC. He has −3 dpt

sphere and −3 dpt cylinder. His corneal thickness is 490 m at the thinnest location. Suppose that CxL with TG PRK are planned. Although the patient has 90 m above the 400 m, still we should be limited to the allowed 40 m of ablation depth. The TG PRK may correct the irregularity of the corneal surface using the 40 m and one may try adding −3 D cylinder to the correction proÞle if the maximal depth of the proÞle does not exceed the 40 m. A smaller optical zone can be chosen to increase the ability to treat the astigmatism, e.g., 6 mm instead of 6.5 mm.

Complications

Complications of CxL are rarely encountered. They include:

(a)Herpetic keratitis with iritis even in patients with no history of herpetic disease, and in cases with an ocular herpes history, systemic anti-herpes therapy is clearly indicated.

(b)Induction of diffuse lamellar keratitis after CxL in a patient with post LASIK ectasia. Using topical steroids should precede CxL in cases of iatrogenic keratoectasia.

(c)Loss in BSCVA of 2 or more Snellen lines after 6 months to 1 year postoperatively. A refractive surgical procedure is considered safe if this complication rate is lower than 5%. Risk factors for visual loss after CxL seem to be (1) age over 35 years and (2) a BSCVA of 20/25 or better. From a strategic viewpoint, it may be that the earlier CxL is performed, the better for the patient.

(d)Failures (failures to stop the progression or failures to achieve the demarcation line): Although failures are not considered complications, they may have an impact on the complication rate. In one study, the only identiÞed risk factor for

failure was a K-max reading greater than 58.00 dpt. The efÞcacy of CxL would likely increase if the treatment was limited to eyes with a K-max reading of less than 58.00 dpt.

(e)Haze: There has been discussion of whether haze is a normal Þnding after CxL and whether the haze affects vision. Although haze occurs after CxL, it usually decreases during the Þrst postoperative year. The haze after CxL differs from the haze after PRK in stromal depth. Whereas haze after PRK is strictly subepithelial, haze after CxL extends into the anterior stroma to approximately 60% of depth, which is on average equal to an absolute depth of 300 nm. The nature of this haze is unclear but may be due to loss of keratocytes or to dehydration.

(f)Corneal melting: It is a rare complication reported following CxL treatment. Frequent instillation of topical anesthetic agents during the procedure, NSAIDs instillation, and Acanthamoeba infection were suggested to lead to the activation of multiple noxious mechanisms that Þnally causes ulceration and corneal melting. Therefore, it is recommended to avoid NSAIDs and contact lenses during the healing process of the epithelium when performing CxL. If prescribed, the patient should be informed of the risk of wearing a contact lens and instructed in its correct use. The risk of bacterial keratitis during the healing process of the epithelium may be greatly reduced with the use of proper prophylactic antibiotic agents, but prophylactic coverage with topical antiamebic and antifungal drugs is not considered. The role of keratocyte apoptosis must be investigated. The patient must be informed of the safety and possible side effects of the therapy. Stressing the importance of avoiding exposure to fresh water while wearing contact lenses is fundamental.

(g)Very rare cases of microbial keratitis with Acanthamoeba and pseudomonas were reported.

3.2.2.6 Intraocular Refractive Lenses

Intraocular refractive lenses (IORLs) or phakic IOLs are lenses used to correct high refractive errors. There are two types regarding the location of implantation: posterior chamber (PC) IORLs and anterior chamber IORLs. There are two types of the latter: angle-supported (AS) lenses and iris-supported (IS) lenses.