Several studies demonstrated that low ocular perfusion pressure is a risk factor for primary open angle glaucoma development and progression. Indeed, studies that evaluated the ocular blood flow have shown the association between the disease and abnormal blood flow parameters. However it is not yet clear how the physicians should intervene in these parameters in daily clinical practice or whether the currently ocular blood flow evaluation provides any additional benefit for the management of the glaucoma patients.
Do you evaluate the ocular blood flow of your glaucoma patients? How do you manage these parameters?
I am a vitreoretinal surgeon and I don't see many glaucoma patients. However I am very interested in studying more the blood flow because I am convinced that high myopes may suffer of insufficient retinal and choroidal blood flow. Some of them in fact loose visual field without an apparent cause. which instrument do you recommend to study the blood flow? can you study also choroidal blood flow?
In NTG patients that progress despite achieving target IOP I search for evidence of poor perfusion by obtaining 24hr BP and diurnal measurements of IOP (especially in patients with systemic hypertension that is being treated with PM or HS medication).
If low systemic BP is detected (and low perfusion pressure) then a discussion with the patients PMD may allow adjustment of any HTN medicines to prevent dips in BP that might compromise perfusion and contribute to NTG.
I don't measure ocular blood flow directly.
JF
I was at one time a MSc student working in a lab focused on measuring blood flow. The instruments we used included the Canon Laser Blood Flowmeter (CLBF) and a more recent acquisition, which at the time of my leaving the lab was being validated against the CLBF, which used spectral domain OCT. My supervisors were Dr. Chris Hudson and Dr. John Flanagan both from the University of Waterloo if you'd like to look into research done by the lab.
Ocular blood fflow is an important parameter in glaucoma disease. It is well known that optic nerve head perfusion is an esential parameter for the viability of the optic nerve axons. There are some devices ( cameras ) that do evaluate ocular blood flow , but there is no a must test in guidelines of good medical practice in glaucoma. It is already known that a medication intended to treat glaucoma must not activate in diminishing the blood flow !
Optic disc has dual blood supply, from central retinal artery( high pressure system) and from short posterior ciliary arteries( ciliary circulation) a lower pressure system compared to retinal circulation. When we talk about measuring ocular blood flow, which one we have in mind, retinal blood flow or ciliary blood flow? which one seems to be implicated in chronic glaucoma?
Although largely discussed in Meetings and editorials, I really don’t think that OBF measurement is indicated for every glaucoma patient.
Even though some populational studies have shown that low BP (or low OPP) seems to be important for both NTG and HTG (POAG) patients, it seems to be more relevant for those developing the disease or progressing despite a low IOP (low teens). In our practice (in São Paulo, Brazil), we obtain 24hr BP and diurnal IOP measurements in these specific cases.
We observe that patients at risk are mostly women, middle aged, Asian descendants and with signs of (primary) vascular dysregulation.
I would also look carefully at those presenting with optic disc hemorrhages.
I recommend papers from Flammer’s group, in Basel, Switzerland.
E.g.: Grieshaber MC, Mozaffarieh M, Flammer J. What is the link between vascular
dysregulation and glaucoma? Surv Ophthalmol. 2007 Nov;52 Suppl 2:S144-54. Review.
I do not measure OPP directly but mathematically using BP and IOP. However, it is impossible to measure OPP 24 hours. Detrimental effect of high IOP and lower BP causing low OPP is usually at night. My current research is measuring inter-visit OPP, preliminary data showed that lower OPP and wider fluctuation in end stage glaucoma. Although mild glaucoma showed higher OPP and there is still fluctuation that perhaps may be responsible for progression of glaucoma
Hi, there are 2 problems: blood flow measurements cannot be achieved just with one machine and what to do then? Of course BP can increases using salt. Anyway it is a promising field in glaucoma.
I measure ocular blood flow in daily clinical practice by laser speckle flowgraphy. Of course, I don’t measure it in every patient, but especially measure when glaucoma progresses in spite of controlled IOP by treatment. If the optic nerve head blood flow is low, I prescribe the drugs (calcium blockers, kalliginogenase, etc.) for increasing it. Measuring by laser speckle flowgraphy is easy and takes only a short time. Please see the review article (Sugiyama, Araie, Riva, Schmetterer, Orgul. Acta Ophthalmol 88:723-9, 2010).
It appears strange that we are talking about various factors in the diagnosis and treatment of glaucoma without working on the real issue: why in glaucoma the nerve fibers are destroyed in a specific sequence, like peripheral fibers first, then paracentral( arcuate) and finally the central fibers. If this was not occurring in specific sequence then we would not be doing perimetry in glaucoma. The reason we are doing perimetry in glaucoma because the nerve fibers are always destroyed in a specific pattern and never haphazardly or randomly.
Now question arises: why is this happening in glaucoma that nerve fibers are always being destroyed in a specific pattern? Once we keep this crucial fact in mind then we can decide whether or not any factor, raised IOP, or ischemia due to poor perfusion or blood flow or neurodegeration of the RGC"s is able to destroy the nerve fibers in a specific pattern.
In my humble opinion there is no known pathology which acting directly will always cause the death first of the peripheral fibers or their RGC"s and would not destroy the nerve fibers randomly. Then why are nerve fibers being destroyed in a specific patten in glaucoma?
It shows that there is a indirect phenomenon or a missing link in glaucoma pathogenesis which is causing the nerve fibers to be destroyed in a specific sequence. Research should concentrate on finding this missing link and leave other things aside for time being. Once we find this missing link then we can talk about other factors. I hope my humble comments make some sense. Thank you.
Yes, we do. NIklas Plange, a clinician scientist in my group is working on it a lot. He can be reached via [email protected]
No, I don't. It has only (from my personal point of view) only academic interest, and no clinical or practical relevance.
I don't evaluate the ocular blood flow of my glaucoma patients, but I prescribe neuroprotective druggs besides lowering IOP
I also do not measure OBF as we dont have laser speckle flowgraphy in our setup. i will be grateful if some one send me the details of instrument regarding its reliability, validity , price etc.
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