Truths, half truths and lesser truths:
A practical guide to the recent clinical trials in glaucoma

Balwantray C. Chauhan, PhD

Abstract:
The recent clinical trials in glaucoma have provided a wealth of confirmatory evidence, as well as new evidence, on the diagnosis, progression and management of glaucoma. This presentation will provide a clinical and epidemiological review, key findings and a critical commentary on how these findings should be translated into practice. Reference will be made to randomized clinical trials in other areas of medicine.

Indices of risk and therapeutic efficacy

Control (CEC) and experimental event rates (EEC)

CEC: The rate at which events occur in a control group. It may be represented by a percentage (e.g. 50%) or as a proportion (e.g. 0.5)
EEC: The rate at which events occur in an experimental group
The patient expected event rate (PEER) refers to the rate of events we would expect in a patient who received no treatment or conventional treatment

Relative and absolute risk reduction

Relative risk (RR): Risk for achieving an event (with treatment) or preventing an event (with prophylaxis) in the treatment group relative to that in the control group
Relative risk reduction (RRR): Reduction in events with treatment compared with control (prophylaxis)
Absolute risk reduction (ARR): Difference in event rates for two groups, usually treatment and control

Number needed to treat (NNT)

NNT: The number of persons who must be treated for a given period to achieve an event (treatment) or to prevent an event (prophylaxis). The NNT is the reciprocal of the absolute risk reduction.

Examples of indices of risk and therapeutic efficacy from OHTS.

Hypothetical examples illustrating interpretation of indices of risk and therapeutic efficacy

Comparison of indices in other glaucoma studies

EMGT
CIGTS
NTGS
AIGS

Comparison of indices in other areas in medicine

Discussion of central corneal thickness and its “risk”

Discussion of the ancillary OHTS study on HRT

Dependence of IOP on progression from AGIS

Problems in elucidating this association from retrospective studies
Problems in elucidating studies whose primary aim was not to answer this question

Discussion on association and contributory cause