• Cataract/Anterior Segment, Glaucoma

    The field of cataract surgery has seen several paradigm shifts that have significantly and irrevocably altered and improved our surgical procedures and outcomes, such as the introduction of the intraocular lens (IOL) by Ridley,1 phacoemulsification by Kelman 2 and viscoelastics by Balazs.3 We believe the field of glaucoma management is about to undergo a paradigm shift that may one day prove worthy of inclusion in this select group of landmark ophthalmic therapeutic advances: the use of selective laser trabeculoplasty (SLT) as primary, secondary and repeat therapy for open-angle glaucoma (OAG), particularly in patients with coexisting cataract. This challenge to the current treatment regimen is possible thanks to recent advances in laser trabeculoplasty research that have resulted in an increase in the use of SLT as both a primary and secondary therapy for OAG.

    Different benefits for different patients

    In patients with glaucoma who have cataract, SLT can be palliative, reducing intraocular pressure (IOP) and postoperative dependency on medications. In patients with cataract who have glaucoma, SLT can be pre-emptive, blunting the possibility of a postoperative IOP spike and reducing dependency on medications to treat transient postoperative IOP elevation.

    In addition to potential clinical benefits, there also is a cost benefit as fewer anti-glaucoma medications are prescribed postoperatively, as well as a compliance benefit, as the medication burden is reduced for glaucoma patients.

    Primary therapy

    As a primary therapy, SLT has been shown to boost the IOP-lowering response when performed prior to the use of ocular hypertensive medications, particularly if prostaglandins are used prior to the initial SLT.4,5 In addition, primary SLT has demonstrated an ability to stabilize diurnal IOP fluctuations.6

    Taking a secondary role

    As secondary or adjunctive therapy, SLT has been found to decrease IOP,7,14reduce use of IOP-lowering medications,8 increase compliance and stabilize diurnal fluctuations in IOP.6,10 SLT as repeat therapy has also shown good results when performed several weeks to several months after initial SLT treatment.

    With success defined as a 20 percent or greater peak IOP reduction, one study found that repeat SLT had a 70 percent one-year success rate and 53 percent two-year success rate.11,12 Another study demonstrated an average decrease in IOP between the first and second SLT treatments of 5.0 and 2.9 mmHg, respectively.12 One research group reported that the time between consecutive SLT treatments did not have an impact on outcomes.25

    Performance similar to medical therapy

    Comparing SLT to medications, one study found the two methods produced a similar drop in IOP, with a mean decrease in IOP of 8.3mmHg in the SLT-treated group compared with 7.7mmHg in the prostaglandin-treated group.13 Similarly, an elegant, randomized trial of 127 eyes treated with SLT or pharmaceutical therapy found no difference in IOP reduction.14

    Reducing IOP and medication use

    SLT is a nondestructive cold laser treatment that uses a low-energy, Q-switched, frequency-doubled, 532-nm Nd:YAG laser.15 The IOP-lowering effects of SLT have been found to be equal to that of argon laser trabeculoplasty (ALT).7,16-19 However, on a cellular level, SLT doesn't scar the trabecular meshwork as does ALT.

    One study used SLT to treat 23 eyes previously treated with ALT, which resulted in a 24 percent reduction in IOP. Similar results have been reported in other studies.10,15,20,21

    The molecular effect of nondisruption to the trabecular meshwork has also been demonstrated in genomic studies. One such effort showed that this physical effect is mirrored in the genome, where SLT produced no changes in mRNA expression.22

    While a 2003 Cochrane analysis suggests data on the duration of SLT's effect is inadequate, our latest data set includes the largest number of SLT-treated eyes with the longest follow-up to date, with 3,034 eyes treated over the course of nine years. We found that mean IOP decreased 31 percent in eyes treated with primary therapy, with a mean follow-up of 757 days. Eyes treated with SLT as secondary therapy experienced a mean IOP decrease of 22 percent over a mean follow-up of 520 days.4

    The mean number of IOP-lowering medications used after treatment with SLT dropped by 41 percent, from 2.3 to 0.9.8 Overall, 57 percent of SLT-treated eyes were able to stop using ocular hypertensive medications altogether.8

    Our data also found repeat SLT to be as effective as primary therapy. We measured a mean IOP decrease of 27 percent after initial SLT compared with a mean IOP decrease of 32 percent after repeat SLT.23

    Our six-year study of SLT as primary therapy is one of the longer studies with continuous follow-up.24 We followed 26 eyes for six years after initial SLT and found a mean IOP decrease of 34 percent, which was maintained over six years.24 When looking at cumulative probabilities of success over the long term, for primary SLT at one, three, five and seven years, success was 97 percent, 93 percent, 82 percent and 52 percent, respectively. For secondary SLT at the same time points, success was 73 percent, 41 percent, 30 percent and 24 percent, respectively. For repeat SLT at one, three and five years, success was 95 percent, 92 percent and 92 percent, respectively.25

    Effective for phakic and pseudophakic eyes

    We also looked at use of SLT in patients before and after cataract extraction and IOL implantation. Our research and the work of other investigators shows that SLT is equally effective at reducing IOP in the phakic and pseudophakic states in the long term; however, SLT is more effective in the short term.26-28 We also found that phakic eyes experience a significantly greater reduction in IOP compared with aphakic eyes (29 percent vs.18 percent).29

    Similar results were observed in a study of pseudophakic patients who underwent ALT, although this study found a larger IOP decrease in psuedophakic eyes compared with aphakic eyes.30

    We also demonstrated that SLT is more effective at reducing medication use in phakic compared with pseudophakic eyes.26

    Good prospects

    While further study with controlled clinical trials is needed to evaluate the benefits and clinical efficacy of SLT in patients with coexisting cataract and glaucoma, the studies we've conducted and discussed in this article suggest a promising, new role and exciting prospects for SLT in these patients. We look forward to the continuing advancement of SLT to treat patients with both glaucoma and cataract.

    References

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