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The concept of 'Quality-of-Life-based Target Pressures' in chronic glaucoma
Stephen A. Vernon
Although first mooted in the 1950s by Chandler, it was only in the 1990s that the term became common in the glaucoma literature, with 126 references being found on a PubMed search in August 2003. Why do we need such a term? If we had a simple, safe, cheap, reliable, and effective method of lowering IOP to a stable 8 mmHg, 'target pressure' as a concept would be redundant. It is because there is often an inevitable 'cost' to the patient in physical (ocular and/or systemic), financial (cost of medications/transport to clinics, or loss of earnings) and psychological terms that the concept has come to such prominence. Currently, a number of definitions exist, most of which are focused on ocular health alone, with some insisting on no progression as a 'sine qua non' (Brubaker, 1996; Hitchings & Tan, 2001; Fetchner & Singh, 2001). Jampel introduced a more whole-patient-oriented definition in 1997 ("That IOP at which the sum of the Health Related Quality Of Life from preserved vision and the Health Related Quality Of Life from not having side effects from treatment is maximized"), but this seems intrinsically difficult to conceptualize with ease either by the ophthalmologist or by his or her patient.
Effectively the term 'target pressure' could be considered an attempt at a holistic estimate of the balance between the risks and benefits of IOP lowering management in an individual (who usually has two eyes). As a result of my experience in compiling the revised 2003 version of the Royal College of Ophthalmologists
Guidelines on Ocular Hypertension and Glaucoma and a recent literature search, I would like to put forward the following definition of 'target pressure':
The IOP ranges for each eye of a patient that are considered sufficiently low at the time of assessment to prevent significant loss of Quality of Life from glaucoma or its management within the patient's expected lifespan.
This concept conveys to the patient that the aim of management is to preserve their Quality of Life (QOL) by means of a flexible management plan for IOP to be agreed upon by both parties, not just to lower IOP in order to prevent ganglion cell loss. It recognizes that treatment, as well as loss of function from glaucoma, can affect QOL, thereby aiding the risk/benefit ratio discussions now commonplace between doctor and patient. It supports a strategy of aggressive lowering of IOP in certain individuals, based on the evidence of studies such as AGIS, as well as a no-treatment scenario in patients in whom the risk of significant visual impairment is low, utilizing knowledge from studies such as EMGT and CNTGS. In order to combat the inevitable sense of failure felt by the patient if a specific IOP level is not attained (and its inherent connotations of a future and sometimes-imminent decline in vision), it also contains the implicit ability of the physician to vary the 'targets' over time, following the analysis of data from the individual being managed.
The above article is based on a presentation made to The European Glaucoma Society Closed Meeting, September 2003.
