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Laszlo
Dosa in Miami A RAFT of new clinical data on the effects of different medical and surgical treatments has significantly increased awareness of the true nature of the course of glaucoma development. Glaucoma specialist Douglas R Anderson MD began the symposium by reviewing the Collaborative Normal Tension Glaucoma Study (CNTGS). Published in 1998 (AJO 1998;126), the study determined that a 30% lowering of intraocular pressure (IOP) can be achieved in NTG patients with medical therapy and laser trabeculoplasty in roughly half the time. Among patients whose IOP has been lowered, the rate of progressive visual field loss was slower than in a control group. On the other hand, untreated NTG patients experienced a highly variable rate of visual field progression. The CNTG study identified several risk factors, which may also be prognostic indicators for the untreated disease. These include migraine, female gender, disc haemorrhage at the time of diagnosis and possibly racial or genetic heritage. The presence or absence of these risk factors, along with other considerations, like the severity of the disease, may assist in making decisions about therapy, Dr Anderson said. Another finding of the CNTG study has been that all patients are not equal. Lowering the IOP may not have the same impact on reducing the rate of damage in all patients and further research is needed to help identify the patient most likely to benefit from lowering the IOP. Paul F Palmberg MD, PhD, reviewed the Advanced Glaucoma Intervention Study (AGIS), a multi-centre clinical trial involving 789 eyes with medically uncontrolled open-angle glaucoma, which was sponsored by the US National Institutes of Health. The patients had been randomised to either argon laser trabeculoplasty (ALT) or trabeculectomy and were followed for several years. At seven years, IOP was reduced on average to 16mmHg by surgery and to 17mmHg by laser. However, cataract risk increased 78% in eyes undergoing trabeculectomy. Moreover, age appeared to be a factor, with younger patients more likely to have failures of surgical treatment than older ones. The AGIS outcome data also showed measurable racial differences. Field loss progressed in 34% of white patients with ALT and in 20% among white patients who had trabeculectomy. The comparable numbers among African Americans were 25% and 24%. Richard K Parrish MD reported on the third trial – the Ocular Hypertension Treatment Study (OHTS). It was designed to determine the effectiveness and safety of lowering IOP in those with a moderate risk of glaucoma. It was the first large-scale study which confirmed that reducing elevated IOPs could delay and possibly prevent the onset of glaucoma. The study showed that for half of those randomised for treatment and whose IOPs were lowered by 20%, the risk of developing glaucoma was about 4.4%. Among those randomised to the observation group, the rate of glaucoma onset was about 9.9% in five years. Lowering IOP resulted in a 60% reduction in the risk of developing the disease. That OHTS data indicated that corneal thickness was an important risk factor in the development of glaucomatous change in the population, along with older age and higher IOP. Race was not a significant risk factor in the study. Black patients had thinner corneas and larger baseline cup-disc rations than white patients. "The conclusion is this: People who are ocular hypertensive and have skinny corneas, who are older, who have larger cup-to-disc ratios, are the ones most likely to get into trouble," Dr Parrish told EuroTimes. The results of the Early Manifest Glaucoma Trial (EMGT), also supported the belief that treatments targeting IOP reduction delay progression of the disease for some patients with newly diagnosed glaucoma. That study compared no initial treatment to treatment with laser trabeculoplasty and IOP lowering medication (betaxolol). The active treatment group saw an average 25% drop in IOP. Long-term follow-up showed a marked advantage for treated patients, who went an average of 66 months before developing glaucomatous changes compared to the control group who showed signs of advancing disease after an average of 48 months. Progression, was also less frequent in the treatment group, with 45% developing signs of progression of glaucoma compared to 62% of untreated patients. However, patients in the active treatment group did appear to be at an increased risk of developing cataract. Each of these major studies answered important questions about the efficacy of treatment approaches for different types of glaucoma. Each of the studies also raises questions about the nature of glaucoma and its treatment. For example, while the studies clearly provide a rationale for the treatment of glaucoma, it is not clear why some patients respond to therapy while others do not. Similarly, questions remain about why some untreated patients progress more slowly than others. And questions also remain about the effects of ethnicity and gender on treatment outcomes and the adverse effects associated with the treatments themselves. The studies appear to provide significant support for early intervention in some patients. New screening techniques may prove very useful in allowing clinicians to recognise the very early signs of disease and to stratify those most at risk. Individualised assessment of risk factors can also help to tailor treatment. The question of optimal therapy remains open, although the consensus is that keeping IOP low is a useful strategy. But just how is still unknown. The prostaglandin analogues are gaining in popularity, in part because they lower IOP by about 30%, whereas the previous first-line choice, beta-blockers, effect only a 20% reduction in pressure. That is an important difference, since several studies have shown that better visual field outcomes were achieved when the pressure was lowered by 30% to 50%, and that the risk of progression is reduced about by 10% to 13% for each additional millimetre per Hg that the pressure is lowered. |
