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Intraocular pressure (IOP) is the measure
of fluid pressure within the eye. The average IOP is 15-16mm
(of mercury) with the “normal” range being up
to 21mm. Only 5% of the population has sustained IOP higher
than 21mm. Where IOP elevation is accompanied by pressure-related
damage to the optic nerve—either structural
damage, as can be observed through the pupil, or functional
damage, as can be assessed by examination of the visual
fields—the diagnosis of glaucoma
is appropriate and treatment to lower the IOP to safer levels
is indicated. Glaucoma, untreated, is among the leading causes
of irreversible blindness in the USA.
Often, the IOP elevation exists initially without signs of
optic nerve damage, raising the suspicion of glaucoma. The
more proper diagnosis in such cases, however, is ocular
hypertension (OHT). OHT, affecting 3 to 6 million
Americans, is acknowledged to be the single most important
risk factor leading to the characteristic pressure damage
to the optic nerve, known as glaucoma. OHT patients are followed
with periodic reevaluation of the visual fields, optic nerve,
and IOP—in most cases without treatment. Some of these
patients eventually go on to develop damage to their optic
nerves and only then is treatment begun.
Waiting for evidence of optic nerve damage before starting
treatment has long been disconcerting to many of us who provide
care to patients “suspect” for glaucoma. Yet the
specter of recommending life-long treatment, with potential
side effects, not to mention cost and inconvenience, based
largely on intuition and empiricism, has been equally disturbing.
Research reported in June, 2002, a “landmark”
6-year study1 of more than 1600 people with OHT (IOP of 24mm
to 32mm), half of whom were treated with eyedrops and the
other half not, concluded that the probability of developing
glaucoma over 5 years was reduced by 60%
in the group receiving treatment. This is the most convincing
study yet indicating the safety and effectiveness of early
medical therapy to delay the development of glaucoma. Mindful
of these impressive findings, we now include more patients
with OHT in the treated population than has been our custom
previously.
1Arch Ophthalmol. 2002;120:1268-1279
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