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Evidence Based Medicine: Glaucoma Studies

The Ocular Hypertension Treatment Study

Study:

  • The Ocular Hypertension Treatment Study (OHTS) determined whether topical ocular hypotensive medications are effective in delaying or preventing the onset of primary open-angle glaucoma (POAG) in patients demonstrating no signs of glaucomatous damage
     

Design:

  • 1636 patients with IOPs ranging from 24-32 mmHg in one eye and 21-32 mmHg in the other eye were selected to receive treatment (any type of commercially available topical hypotensive. 817 patients), or observation (no treatment, 819 patients)

  • Goal: Reduce IOP by 20% or more in treated group
     

Findings:

  • The mean IOP reduction in the group that received treatment was 22.5% compared to the group that did not receive treatment (4%)

  • At the five-year follow-up, the probability of developing POAG was 4.4% in the treated group vs. 9.5% in the group left untreated.

  • Repeatable visual field defects and optic nerve head deterioration was less noticeable in the treated group
     

Implications:

  • Ocular hypotensives were very effective in delaying/preventing the onset of POAG in individuals with NTG

  • In a subsequent OHTS report, central corneal thickness (CCT) was found to be a powerful predictor for development of POAG; the risk of POAG was inversely related to CCT. Patients with CCT < 555um were three-times more likely to develop POAG than patients with CCT> 588um.

 

 
Glaucoma Laser Trial

Study:

  • The Glaucoma Laser Trial (GLT) compared the safety and efficacy of argon laser trabeculoplasty (ALT) as an alternative to topical glaucoma drops as initial therapy in treating patients with POAG
     

Design:

  • 271 patients with newly diagnosed glaucoma

  • One eye received timolol maleate 0.5%; the fellow eye was treated with ALT
     

Findings:

  • 2-year follow-up: Eyes treated with ALT had a 1-2 mmHg additional IOP decrease and required fewer prescriptions of two or more medications compared to eyes treated with timolol maleate 0.5% alone.

  • 44% of eyes at the end of two years were controlled by ALT alone

  • 70% of eyes at the end of two years were controlled by ALT and timolol maleate 0.5%

  • 30% of eyes at the end of two years were controlled with timolol maleate 0.5% alone

  • Visual acuity and visual field testing showed no significant difference between the two groups

  • At the seven and nine-year follow-ups, no significant differences in CD ratios were noted between the two groups
     

Implications:

  • This study was completed prior to the advent of prostaglandin analogues, topical CAIs, and alpha-agonisits, but suggests ALT may be an alternative as initial glaucoma therapy

 

 
The Collaborative Normal-Tension Glaucoma Study

Study:

  • The Collaborative Normal-Tension Glaucoma Study (CNTGS) aimed to determine whether IOP is a factor in the pathogenesis of normal-tension glaucoma (NTG).
     

Design:

  • 140 patients with NTG and high-risk VF defects: 79 (56%) eyes were randomized to receive no treatment. 61 (44%) eyes were randomized to receive treatment (medications, laser, and/or surgery to decrease IOP 30% from baseline)
     

Findings:

  • Compared to the untreated group, there was a statistically significant favorable effect in eyes that had an IOP reduction of 30% or greater from baseline on visual field and optic nerve deterioration.

  • 65% of patients in the untreated group showed no progression of their disease in the follow-ups
     

Implications:

  • IOP is involved in the pathology of NTG, therapy is effective in lowering IOP, and a 30% reduction is beneficial to patients to prevent glaucoma from progressing.

  • Because a significant amount of patients left untreated showed no exacerbation of their disease at follow-ups, a choice of therapy must be carefully thought out.

 

 

Collaborative Initial Glaucoma Treatment Study

Study:

  • The Collaborative Initial Glaucoma Treatment Study (CIGTS) sought to determine if medication or filtering surgery (trabeculectomy) was more beneficial as initial treatment of glaucoma.
     

Design:

  • 607 patients with newly diagnosed open angle glaucoma

  • One eye from each patient was selected to receive topical medication; the other eye underwent surgery (trabeculectomy)

  • Patients were evaluated every six months for five years
     

Findings:

  • Visual field loss did not significantly differ between the two groups after five years

  • Surgically treated patients had an initial increased risk of substantial visual acuity loss compared with eyes treated topically

  • At the four-year follow-up average visual acuities between the two groups were the same

  • The surgically treated group had on average a 3.5 mmHg additional IOP decrease compared to the topically treated group, but had a greater rate of cataract surgery
     

Implications:

  • Initial medication and surgical treatment showed similar end-results in visual field outcomes and final visual acuities

  • Aggressive IOP lowering in both groups minimized visual field loss

  • The researchers concluded that changing the recommended “medication first” approach was not warranted

 

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Early Manifest Glaucoma Trial

Study:

  • The Early Manifest Glaucoma Trial (EMGT) compared the effect of immediately lowering IOP vs no treatment of later treatment on the progression of newly detected open-angle glaucoma (OAG)

 

Design:

 

  • A significant amount of patients diagnosed with NTG were randomized to receive treatment (laser trabeculoplasty plus topical betaxolol) or no treatment.
     

Findings:

  • Treatment lowered IOP by roughly 5 mmHg (25% reduction)

  • Glaucomatous progression was seen less frequently in treated patients (45%) compared to those patients that were not treated (62%).
     

Implications:

  • After six years, glaucomatous progression was less in the treated vs untreated group

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