As universally acknowledged, argon laser trabeculoplasty (ALT) exerts thermal damage to the treated TM, causing the shrinkage of collagen fibres, stretching and widening the adjacent areas and allow more outflow(11). Compared to ALT, SLT’s energy selectively absorbed by pigmented trabecular cells and makes no damage to adjacent structures. Both ALT and SLT provided reliable IOP-lowering effect, but ALT caused obvious damage to TM histologically(11, 12). Several clinical trials claimed that SLT was an effective way to control IOP in multiple types of glaucoma(13-17). However, a wide range of complications, such as redness, photophobia, peripheral anterior synechiae, and cystoid macular oedema were still observed in patients with SLT (18).
Unlike the former laser technologies, MLT is based on a micropulse laser with a 15% duty cycle, which allows the temperature to return to the baseline. Under this condition, both TM and Schlemm’s canal could escape from cellular damage, scarring, and morphological changes(19).
Previous research demonstrated that MLT (810nm) was less effective in reducing IOP compared with ALT on a 3-month visit(20). A retrospective review was conducted by Rantala, in which they evaluated 180° MLT (810nm, 180°) on patients with OAG with a minimum follow-up period of 6 months, and found that MLT was a safe but not effective-enough treatment for glaucoma(4). Lee investigated the use of 360° MLT (577nm) for treating patients with OAG. By the end of the 6-month visit, 72.9% of patients were successfully treated(5). Abramowitz carried out a prospective randomized clinical trial, comparing 360° MLT (577 nm) with 360° SLT. He showed that MLT was as effective as SLT within a 52-week follow-up period(21). Valera-Cornejo conducted MLT (532nm, 360°) on patients with OAG and found that it reduced IOP in a pretty short period(6). All of the above indicated that both the range and the wavelength of laser applied to patients may affect the results. In the present study, IOP was averagely reduced by 3.73%, and only 21.88% of the patients achieved a more than 20% reduction in IOP by the end of the 35-month visit. This result was not as encouraging as the previous findings. Recently, several studies claimed that MLT is a safe and effective way to attenuate IOP, while the observation period were relatively short(8, 22-24).
The present study had several limitations. Initially, this was a small-sample study. Patients’ characterizations, such as the optic nerve condition, might have affected the results. Seven eyes with a C/D ratio range from 0.9 to1.0 were enrolled, four of them underwent trabeculectomy, demonstrating a poor prognosis. The reason why we recruit them is because several anti-glaucoma drugs had been prescribed but not sufficient to lower the IOP in these patients. To reduce the glaucoma medications and slow down the progression of optic nerve damage, we decided to perfume MLT to these 4 eyes. Secondly, given the relatively long follow-up period, it was hard for patients to completely following doctors’ instructions. Especially, those who still have a relatively good visual acuity, might not apply drugs as routinely as required, leading to an under-estimated IOP-lowering effect.
To our knowledge, this research was one of the longest explorations of the effect of MLT on patients with glaucoma and OH, claiming that a single session of MLT could significantly reduce IOP in a pretty short period. Given the repeatability of MLT, it could be used as an IOP-lowering treatment.