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The clinical significance of quality of life (QoL) studies in glaucoma has been described before.1 In brief, they attempt to quantify visual ability (VA) and activities of daily living (ADLs). Moreover, using correlations and regression analyses it is possible to correlate VA and ADLs with a series of clinical indexes in an effort to evaluate the impact of glaucoma on visual function. However, further to their importance in cross-sectional settings, QoL outcomes do provide an insight about the patient's progression, as well.

The European Glaucoma Society in their latest publication suggested the fundamental framework on glaucoma progression2 based on prospective studies that assessed the difference between predicted and estimated visual fields (VF) damage.3 According to these studies, each glaucoma patient demonstrates a variable but linear deterioration of his/her VF. By means of repeated VF examinations, the determination of the rate of progression becomes possible. The projection of the progression line into the future allows the assessment of the risk for visual impairment (VI) within the expected life span of the patient.

Unfortunately, despite its unquestionable validity and usability, the proposed methodology actually provides information only on the progression of the VF and not of the overall visual functional status of the patient. This important remark should be clear to the ophthalmologist when planning or modifying the treatment strategy, because although mean deviation (MD) or visual fields index (VFI) deteriorate linearly in the majority of glaucoma patients, VA demonstrates a non-linear deterioration. In fact VA and MD demonstrate a quadratic correlation.4 Actually, the complex relationship between VA and MD or VFI within the continuum between time of diagnosis and the expected time of death is presented in the Eye Institute of Thrace glaucoma progression diagram (EIT-GPD) (Fig. 1); which is a simple modification of the regression analysis diagram by Labiris and co-workers.4Figure 1 presents hypothetical scenarios of three patients with different progression of VF. Case 1 scenario represents a patient with a rapid deterioration of VF who, according to the methodology of the European Glaucoma Society (EGS) will reach VI within his/her life span, whereas cases 2 and 3 scenarios represent patients with less rapid deterioration of their VF who will not reach the VI line within their expected life span. Stripped lines represent the corresponding VA scores with respect to the quadratic relationship of VA and VFI.

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Figure 1. Glaucoma progression diagram.

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EIT-GPD has the following important clinical implications: (i) Glaucoma patients demonstrate an accelerated deterioration of their VA as VF worsen linearly; (ii) Steeper VFI lines (i.e. rapidly progressing patients in terms of VFI) result in even more aggressive deterioration of their VA; (iii) In terms of VA the patient will reach the VI line sooner; (iv) A significant percentage of patients who were supposed to avoid VI (by simple projection of the VFI line) will actually become visually impaired unless more aggressive treatment is planned (Case 3 scenario).

The fundamental advance of the EIT-GPD over the corresponding EGS progression diagram is that further to the linear deterioration of the VF, EIT-GPD incorporates the quadratic relationship between VA and VFIs. Due to this fact it reflects more accurately the visual functional ability of the patient within the disease continuum. However, because the EIT-GPD was developed by projection of cross-sectional data into future, prospective studies are needed in order to confirm its validity with actual measured data.

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