Dear editor,

We want to thank Drs. Martinez and Sanchez for the response to our recent editorial. We are in agreement with them that evidence does exist that blood flow is altered in glaucoma and is suggestive of a pathogenetic role[1]. We also agree that a variety of methods are being used to evaluate blood flow and these techniques certainly have improved over the last decade and a half.

I would also like to thank Drs. Martinez and Sanchez for calling attention to their article in Acta Ophthalmologica[2] detailing their prospective analysis of blood flow in glaucoma. They are to be congratulated on their work. Unfortunately, in an editorial, space is limited and not all research could be highlighted to the extent that we would have desired.

The article mentioned by Dr. Martinez and Sanchez is an elegant early step in attempting to prospectively determine blood flow-based risk factors for progression over the mid-term in patients with untreated primary open angle glaucoma. In the 49 patients evaluated by the authors(23 progressed and 26 non-progressed over three years) differences in resistivity index as measured with color Doppler, but not baseline intraocular pressure as in the Early Manifest Glaucoma Trial, predicted approximately 80-90% of patients who ultimately progressed or remained stable[2,3].

This work highlights ocular hemodynamics as a possible risk factor for glaucomatous progression. Their response letter confirms the need for a more definitive evaluation of blood flow in glaucoma to determine any relationship to its pathogenesis and if improving this parameter improves long-term visual outcomes. By doing so we hope that, in the future, our patients may be more specifically and adequately treated.

References
1. Stewart WC, Feldman R, Mychaskiw MA. Ocular blood flow in glaucoma: the need for further clinical evidence and patient outcomes research. Br J Ophthalmol. 2007; 91: 1263-1264.

2. Martinez A, Sanchez M. Predictive Value of Color Doppler Imaging in a Prospective Study of Visual Field Progression in Primary Open-Angle Glaucoma. Acta Ophthalmol Scand 2005; 83: 716-723.

3. EMGT

William C. Stewart M.D. Charleston

Dear Editor:

We read with great interest the recent commentary by Stewart et al [1] describing the evidence of the blood flow disturbances in the pathogenesis of the glaucomatous damage. Although I agree with some of the findings of this excellent review, there are some important points that should be addressed:
1.After reading this article, one may think that there is not evidence that ocular blood flow abnormalities are involved in the pathogenesis of the glaucomatous damage. Different studies, using different devices, point in the same general direction indicating that on average blood flow is decreased in some glaucoma patients, especially in primary open-angle glaucoma (POAG) patients and in patients that progress despite normalized intraocular pressure (IOP) [2]. Furthermore this decrease in blood flow is not confined to the eye alone [3].
2. Many different methods are being used to measure directly or calculate indirectly in vivo ocular blood flow. Although there is not still a single method that can provide all the relevant information in one reading, the development of newer techniques and their corrected use provides the potential for assessing blood flow in humans.
3. On the other hand, the Authors reveal the lack of evidence of a pathogenic link between glaucoma and impaired ocular blood flow. They asked for a long-term prospective study, that includes carefully selected patient groups, with similar baseline demographic and clinical characteristics, but with dissimilar baseline ocular hemodynamics. We published a paper that prospectively investigated the value of color Doppler imaging of the ophthalmic artery and short posterior ciliary arteries in the prognosis of disease progression in patients with POAG. [4] When baseline demographic and clinical characteristics were stratified according to whether the eyes progressed during the 3-year follow-up period, the only parameters to show significant differences were the resistivity index of the ophthalmic artery and the resistivity index of the short posterior ciliary arteries. Our study concluded that poor blood flow in the retrobulbar vessels is closely linked to visual field deterioration in POAG patients.

In conclusion, we think that the understanding of the role of ocular blood flow disturbances in the pathogenesis of glaucoma has improved greatly. We have evidence that ocular blood flow is altered independently from IOP or level of damage in patients with progressive glaucoma, which could represent a primary risk factor for disease progression. In looking forward, we need long-term prospective multicenter studies to evaluate both the impact of ocular blood flow in glaucoma and the benefit of improving ocular blood flow.

References

1. Stewart WC, Feldman R, Mychaskiw MA. Ocular blood flow in glaucoma: the need for further clinical evidence and patient outcomes research. Br J Ophthalmol. 2007; 91: 1263-1264.

2. Flammer J., Orgül S., Costa VP., et al. The impact of ocular blood flow in glaucoma. Prog Retin Eye Res 2002; 21: 359-393.

3. Gasser P, Flammer J. Blood-cell velocity in the nailfold capillaries of patients with normal-tension and high-tension glaucoma. Am J Ophthalmol. 1991; 111: 585-588.

4. Martinez A, Sanchez M. Predictive Value of Color Doppler Imaging in a Prospective Study of Visual Field Progression in Primary Open-Angle Glaucoma. Acta Ophthalmol Scand 2005; 83: 716-723.