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STEROIDINDUCED GLAUCOMA AFTER REFRACTIVE SURGERY
Steroids are commonly used after LASIK to reduce the synthesis of collagen, decrease corneal haze and avoid myopia relapse. Although many researchers reported that steroids did not improve corneal haze after PRK, topical and oral steroids are being used with large amount and high frequency in the management of postoperative DLK, which has an incidence ranging from 0.75%32%. It is more dangerous for patients with glaucoma to use steroids which can induce IOP elevation. Galal et al[40] retrospectively studied 11 cases of DLK after LASIK who had steroidinduced IOP elevation and consequently developed flap interface fluid and corneal edema. After steroids was tapered off and replaced by aqueous suppressants, the interface fluid was cleared and IOP became normal. Severe steroidinduced glaucoma can apparently damage the visual function. Davidson, Brandt & Mannis[41] reported that when a patient took steroids for DLK after LASIK, his optic nerve was damaged by steroidinduced glaucoma. Shaikh et al[42] reported two steroidsensitive patients who developed endstage glaucoma after LASIK requiring trabeculectomy to control IOP.
The manifestation of steroidinduced glaucoma is similar to primary open angle glaucoma (POAG), but postoperative optic papilla change of high myopia is different from that of POAG, without deepening and enlargement of optic cup, which is not easily identified. Probably it is because high myopia is vulnerable to elevated IOP. Therefore it is not wise to judge the optic papilla damage of steroidinduced glaucoma in myopia patients according to the changes of optic papilla.
The clinical manifestation of pressureinduced interlamellar stromal keratitis (PISK) is similar to DLK, which is characterized by corneal opacity without clear reasons. Topical steroids are not only ineffective, but also may aggravate the corneal haze and increase IOP. Elevated IOP for a few weeks may cause optic nerve damage and visual field defect, which can be solved by decreasing the dose of steroids and administering aqueous suppressants. Miyai et al[43] reported two cases with PISK after LASIK and found that using aqueous suppressants instead of steroids was effective to clear interface fluid and decrease IOP. Cheng et al[44] studied two cases of steroidinduced glaucoma after LASIK by confocal microscopy and found that it was no related to inflammatory cells in the flap interface.
For patients after refractive surgery, it is recommended to use steroids that are of low density and with less sideeffect of increasing IOP, and the time cant last too long. Once IOP elevation occurs, steroids should be stopped. After refractive surgery, it is a routine to measure IOP regularly. It should be more prudent to perform LASIK for patients with one eye high myopia (the other eye is blind).
CAN KERATOREFRACTIVE SURGERY BE DONE IN PATIENTS WITH GLAUCOMA?
Glaucoma is not an absolute contraindication to LASIK, but a relative contraindication. The disadvantages of patients with glaucoma undergoing LASIK are as follows: 1) Eyes with glaucomatous nerve damage are more sensitive to the transient IOP elevation in the surgery, which could cause the damage of optic nerve and visual field[35]. 2) The use of steroids after surgery could aggravate the elevated IOP. Furthermore, patients with glaucoma are more sensitive to steroids, and hence the risk of steroidinduced glaucoma and damage of visual function are much greater than general population. 3) IOP elevation could cause the relapse and development of myopia, which is a main reason for the regression after LASIK. 4) The risk to the filtering bleb with the microkeratome makes LASIK a contraindication in most cases, and PRK would be preferable, if any keratorefractive surgery is to be used. Further caution is required when prophylactic mitomycin C is employed with PRK[3]. In summary, high IOP not only affects the postoperative application of steroids, but also could cause regression. Therefore, intensive perioperative counseling and informed consent is mandatory.
For the sake of safety, preoperative IOP should be controlled in normal range, preferably lower than 24mmHg, because Some reports show that the incidence of POAG is much higher among people whose IOP is higher than 26mmHg. Secondly, preoperative ratio of C/D should be less than 0.5, with normal visual field. Thirdly, surgeons should shorten the time of vacuum suction. Corneal thickness could be used as a predicting factor for the prognosis, and therefore preoperative CCT measurement is important to patients with high IOP, which could predict the risk of POAG. The difference between preoperative and postoperative IOP is useful to guide the postoperative steroids use. Once dangerously high IOP appears, steroids should be stopped immediately, in case further damages occur to optic nerve.
TREATMENT FOR THE ELEVATED IOP AFTER REFRACTIVE SURGERY
There is no evidence that patients undergoing refractive surgery with postoperatively elevated IOP should have special medical management protocols different from chronic glaucoma. Nagy et al[45] compared timolol (twice per day), dorzolamide (three times per day) and combined timolol and dorzolamide (twice per day) in patients after PRK and found that the combination was the most effective. Vertugno et al[46] reported that latanoprost 0.05g/L and timolol maleate 5g/L were effective in lowering IOP after PRK. In recent years, the treatment for managing the rise of IOP has greatly improved and physicians should be aware of the contraindications and side effects of those drugs. In brief, treatment for the elevated IOP after keratorefractive surgery is similar to those for patients with glaucoma.
In conclusion, patients with glaucoma require considerable preoperative counseling and postoperative monitoring. Furthermore, postoperative steroids and underestimation of tonometric IOP measurements are extremely important considerations. Keratorefractive surgery influences the accuracy of GDx measurements of the RNFL, but there is no significant change in the RNFL measurements after LASIK using GDxVCC apparatus. Glaucoma medications in the management of patients who have had keratorefractive surgery are similar to the medications used in other glaucoma patients. The present data regarding the safety of keratorefractive surgery in patients with glaucoma show that glaucoma is not an absolute contraindication to LASIK, but a relative contraindication.
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