Laser in situ keratomileusis (LASIK) is currently the most popular refractive procedure. Most cases are eventless and provide excellent refractive results. Nevertheless, anecdotal reports have been published showing that LASIK's transient elevation of intraocular pressure (IOP) during suction ring application can have potential deleterious effects on patients, namely retinal breaks and detachments, macular hole formation, Bruch's membrane rupture with subsequent choroidal neovascularization and optic neuropathy.^1,2

Some studies have supported the idea that there is no deleterious effect on retinal nerve fibre layer (RNFL) thickness after LASIK.^3,4 Even so, some concern still exists about the possibility that such barotrauma may cause detrimental ganglion cell loss. Taking this into account, there is a trend not to submit glaucoma patients or glaucoma suspects (such patients have increased susceptibility for ganglion cell loss) to refractive procedures characterized by transient IOP elevation (LASIK and epi-LASIK) but instead to choose alternative refractive procedures which do not imply intraocular hypertension (PRK or LASEK).⁵

Figure 1: OCT retinal nerve fibre layer data.

Considering all available data, it seems important to the authors to bring this issue to discussion once again.

Assessing RNFL

There are mainly two kinds of exams used to assess RNFL damage. On one hand, we have the functional exams and, on the other hand, the structural ones. Both types are depicted in Table 1.

Diagnosing RNFL loss by assessing structural changes seems to be more sensitive than their functional damage.⁶ Subsequently, most published studies have used structural means to assess early RNFL damage. OCT and GDx seem to be more suited to peripapillary RNFL measurements rather than HRT, which is primarily designed for disk morphology evaluation. It is mandatory, however, when using the GDx, to have the variable corneal compensation (VCC) upgrade. The VCC upgrade allows a reliable measurement of RNFL thickness independently from birefringence changes of the cornea subsequent to previous keratorefractive surgery.^7,8,9

So, the present study was conducted to evaluate and compare the effect of LASIK and PRK on the peripapillary RNFL using the new TOPCON 3D-OCT.

Table 1: Ways to assess retinal nerve fibre layer damage.

Forty eyes of twenty myopic non-glaucomatous patients were submitted to LASIK (Group 1, n=20) and to alcohol-assisted-PRK (Group 2, n=20). In Group 1, a 180 µm Hansatome head was used. Each patient was submitted to both procedures (one eye each). No intraoperative or postoperative complications were observed in either group.

All eyes had their RNFL thickness measured by OCT preoperatively and postoperatively (1 day, 1 month, 3 months). The measurements were then statistically compared using an unpaired t test. A p value <0.05 was considered significant.