When Medical Therapy Fails

A surgical procedure is indicated when medical therapy no longer adequately controls IOP. While some feel surgery should be the initial treatment for glaucoma, most clinicians in the United States use LTP, either with an argon laser (argon LTP [ALT]) or a frequency-doubled Q-switched Nd:YAG (neodymium-doped yttrium aluminum garnet) laser (selective LTP [SLT]), and trabeculectomy when medical therapy fails. Although the Glaucoma Laser Trial has shown at least equal efficacy for initial medical therapy and for initial ALT, ALT causes a permanent anatomic alteration of the body and has potential significant adverse effects.22 Although the likelihood of such serious ALT side effects is small, most clinicians in the United States favor reserving ALT until after medical therapy has failed. An even stronger statement can be made for withholding filtering surgery until after the failure of medical therapy and ALT. Filtration surgery is at least as effective at IOP reduction as medical therapy, perhaps even more so.23 However, the potential adverse side effects of filtration surgery make topical therapy a favored first-line option.

Which procedure to choose when disease can no longer be controlled with medications will depend upon the type of glaucoma, the severity of disease, and the patient. LTP is a less invasive procedure than filtration surgery and is often the initial surgical intervention performed. It is an effective IOP-lowering procedure in patients with primary open-angle glaucoma, pigmentary glaucoma, and pseudoexfoliation glaucoma.24 LTP is less effective in patients with congenital or juvenile open-angle glaucoma, angle recession, and uveitic glaucoma.25 ALT reduces the IOP in approximately 85% of all patients 1 year after treatment and has an efficacy of 50% at 5 years26,27 Initially, IOP reductions range from 20% to 30% or a mean of 9 mm Hg.28 In patients who have difficulty complying with complicated medication regimens, LTP may be helpful in reducing the number of glaucoma medications needed to achieve IOP control. LTP in combination with medical therapy has been shown to control IOP in a slightly higher percentage of patients than medical therapy alone.28 However, LTP does not reveal its maximal pressure-lowering effect until 4 to 6 weeks after treatment. In patients with rapidly progressing disease and severe field loss, this latency period may allow further damage to occur. In such patients, filtration surgery is a better option. It has also been shown that patients with higher IOP—greater than 35 mm Hg—have a higher failure rate with LTP, mainly because the absolute pressure reduction is not adequate even though a 40% to 50% change may be evident after the procedure.29,30

Complications of LTP include corneal irritation or abrasions, mild postoperative iritis, peripheral anterior synechiae, or worsening of glaucoma. In addition, a steroid response can occur, since topical steroids are usually used to suppress postoperative inflammation. The most common adverse effect of LTP is a rise in IOP usually seen in the immediate postoperative period in approximately 20% of patients.31 This transient rise in IOP has been associated with loss of visual field.32 Apraclonidine and brimonidine are the most effective at preventing postoperative IOP spikes after LTP.33,34 In patients with severe disk damage and field loss from glaucoma, LTP is still a viable treatment option as long as postoperative IOP is monitored closely during the first 24 hours.

LTP has traditionally been done using an argon laser. Recently, SLT has found a role in treating glaucoma patients. SLT uses a Q-switched, 3-nanosecond, frequency-doubled Nd:YAG laser that delivers a fraction of the laser energy (<1%) to tissue compared to ALT. The short pulse of energy delivered to the target is shorter than the thermal relaxation time of tissue, resulting in selective photothermolysis, minimizing generalized destruction and collateral damage.35

Latina et al.35 were first to describe SLT for use in decreasing IOP in a group of glaucoma patients, including those with previous ALT or history of maximal medical therapy. Since its introduction, multiple studies have been done to support the clinical efficacy of SLT compared to ALT and medical therapy. Prospective studies have indicated that SLT can decrease IOP by 30% to 35% when used as primary therapy. Melamed et al.36 showed that SLT is safe and effective as primary treatment for open-angle glaucoma in eyes not previously treated with medicines. IOP dropped an average of 7.7 ± 3.5 mm Hg after SLT. In addition, when comparing SLT to ALT, a similar IOP-lowering effect is demonstrated with long-term follow-up.37,38

In histological evaluation done by Kramer and Noecker,39 less structural damage to the trabecular meshwork was witnessed after SLT in comparison with ALT. Scanning electron microscopy of human cadaver eyes following ALT and SLT revealed coagulated tissue and crater formation with the former and no significant physical alteration to the meshwork in the latter. This makes SLT a potentially repeatable treatment, although this hypothesis requires further study and long-term follow-up.

When LTP (argon or selective) fails to control IOP or if a patient is a poor candidate for laser surgery in the setting of failed maximal medical therapy, the procedure of choice is usually trabeculectomy.

0 0

Post a comment