LASIK, that can allow uncover part of cornea

LASIK, RK, and other refractive surgery usually gives a successful results in correcting the refractive errors. However, some of the surgeries did not give successful results because of the complications of surgery. The results depend on how the corneas respond to incisions, laser and how the eyes heal after a surgery.  

       Radial keratotomy is a one of refractive surgery that involving tiny cuts around the cornea, which to flatten it and reduce myopia. It cuts through more 90% of the thickness of the cornea. These will cause central corneal to flattening and occasionally reduce myopia. The vast majority of RK patients regressed. Most became very farsighted and astigmatic and required treatment. After a long term, complications of RK include includes visual acuity reduce, irregular astigmatism, over-correction, under-correction, and hyperopic shift. The hyperopic shift happens because of low corneal rigidity and increased in intraocular pressure.

       Referring to this case, the patient was diagnosed as having hyperopia with astigmatism following RK due to flattening and irregular of the cornea.  Optic zone diameter of the patient is smaller, which is less than 3.00mm, this can create corneal irregularity that can result in visual distortion and blurry vision. These irregularities of the cornea can caused wavefront aberrations and scattering errors that will reduce visual quality. The patient is intolerance with spectacles as the prescription of spectacles did not improve her visual acuity. Furthermore, spectacles prescription can do nothing to change corneal irregularities, cannot correct the vision problems because of these irregularities. Spectacles only can correct uncorrected  refractive errors such as myopia, hyperopia and astigmatism.  Then, this patient is corrected with contact lenses.   

      The patient was given an RGP lens because gas permeable contacts are rigid, it can maintain their shape on the eye, unlike soft lenses, it losing their shape when the lens placed on the cornea.   RGP are better than SCL as it contains high Dk/t, less corneal coverage that can allow uncover part of cornea received oxygen normally and also it can make greater tear exchange because of the smaller diameter of RGP. This greater tear exchange can reduce the aberrations because the tears fill in the cornea irregularities, effectively will improve the vision. However, patient’s eye cannot capable with RGP lenses as it gives poor fitting and examiner noted markedly decentration of the lens. This is because RGP lens did not have a sufficiently flat base curve due to central cornea flattening.   

       After applying RGP lenses, examiner applied a plus spherical power contact lens (PSSCL) to the patient. PSSCL which is thick at the center and can correct the hyperope and low-graded astigmatism simultaneously. This will make the lenses gives better centration and stable tears. When fitting the eyes with PSSCL, it showed slightly inferior decentration also with good. The patient’s visual acuity after corrected with PSSCL was 0.0 logMAR (6/6) on her both eyes. Moreover, PSSCLs are easy to apply and easily to adapt when comparing to RGP lenses. After considering the living habits of the patient, daily disposable SCL are most suitable to prescribe for her.

       Contact lenses, including orthokeratology CLs, and hybrid lenses, also may provide a strategy for refractive correction of hyperopia and astigmatism following RK. Ortho-K is a type of gas permeable that can reshape contour of the cornea that can reduce myopia. It also eliminates the need for glasses or daytime contact lenses. The Ortho-K uses specially designed GP to reshape the curvature of cornea and improve vision. This contact lenses are worn overnight. The Ortho-K has a central zone that is relatively flat compared with the periphery, and it is, therefore, suitable to the shape of the post-RK cornea. However, the lens seemed to be ineffective in the long term. Besides Ortho-K, hybrid lenses also can be an options to used for post-RK hyperopia. However, both Ortho-K and hybrid lenses have drawbacks in that, so it is more expensive and have limited product specifications. PSSCL is more affordable when compared with these lenses.   

      Besides, the patient also can be corrected by using surgical method instead by using contact lenses. The surgical method that will be used includes LASIK, INTACS or PRK. These irregularities sometimes can be corrected with a follow-up laser procedure which called an enhancement.  But if the cornea is too thin for a second surgery, or other problems rule out an enhancement procedure, contact lenses may be the best solution. Moreover, second surgical procedures only made things become more risky. This is because LASIK and other laser vision correction procedures alter front surface of cornea by removing microscopic amounts of tissue from the cornea. Then, this can cause a reduction in vision after surgery because of irregularities and thin cornea.        

     Others complications of post-RK to the visual performance includes double or triple vision, irregular astigmatism, unstable or fluctuating vision, halos and glare and reduced night vision and the eventual need for corneal transplant surgery.