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The ophthalmodynamometer

For long the following equation has been presumed : PP =MAP – IOP (PP: perfusion pressure, MAP: mean ophthalmic artery pressure, IOP: intra-ocular pressure).


However some years ago one realised that in some instances the retinal venous pressure (RVP) in the prelaminal layer of the optic nerve head is much higher then IOP. 
Thus the correct equation then becomes: PP= MAP – RVP 1

This finding is important in the management of glaucoma and retinal diseases (eg. DRP, CRVO).
RVP at the optic nerve head is measured by ophthalmodynamometry. 


As a clinician, you want to be able to detect high risk eyes. 


Ophthalmodynamometry enables you to manage your patients more succesfully. 


1 The effect of nifedipine on retinal venous pressure of glaucoma patients with the Flammer-Syndrome. Fang L et al. Graefes Arch Clin Exp Ophthalmol. 2015 Jun;253(6):935-9
 

•    If no spontaneous venous pulsations are seen, this means RVP is higher than IOP.
•    Central retinal venous pressure is higher in glaucoma patients than in healthy subjects and is higher in the eyes with the larger excavation in patients with unequal excavations.1 
•    The central retinal venous pressure is a considerable risk factor for the progression of glaucoma damage.1 
•    IOP lowering therapy only is ineffective in eyes in which RVP is higher than IOP, which may apply to about 40-50% of glaucoma patients.1
•    Pulsation of the central retinal vein is absent in about half of the glaucoma patients.2 
•    A worse visual field mean deviation has been found to be strongly predictive of a higher pressure in the central retinal vein (central RVP).2,3
•    Higher pressures in upper and lower hemiveins is found to be strongly associated with a worse mean deviation in the corresponding hemifields.2,3 
•    In two studies RVP was up to 25 mmHg higher in the median than the IOP.2 
•    A Long-term study of 82 months has shown that the central RVP is strongly predictive of an increase of optic disc excavation.2
 

The ophthalmodynamometer will enable you to assess RVP at the optic nerve head in both upper and lower retinal hemivein and manage your patients accordingly.

 

1 Stodtmeister R,  The pulsation and the pressure of the central retinal vein and their relation to glaucoma damage and therapy. Klin Monbl Augenheilkd. 2008 Jul;225(7):632-6. 

2 Stodtmeister R  Central retinal vein: its pulsation and pressure in glaucoma. Klin Monbl Augenheilkd. 2015 Feb;232(2):147-51. 

3 Morgan WH et al. The force required to induce hemivein pulsation is associated with the site of maximum field loss in glaucoma. Invest Ophthalmol Vis Sci. 2005 Apr;46(4):1307-12.

•    In diabetes patients with diabetic retinopathy (DRP), RVP is markedly and significantly increased, and this result is found to be significantly age dependent.1 
•    RVP is not increased in diabetes patients without DRP.1
•    A marked increase in RVP in diabetes patients with DRP is clinically relevant, as it reduces perfusion pressure and increases transmural pressure. Reduced perfusion pressure contributes to hypoxia and the increased transmural pressure can facilitate retinal edema.1
•    Eyes with increased RVP after more severe CRVO demonstrate significantly reduced vision, reduced retinal blood flow, a higher incidence of rubeosis iridis, and larger areas of capillary nonperfusion that correlate with the degree of RVP elevation.2
•    In patients with CRVO, the RVP is increased in both the affected as well as in the unaffected contralateral eye.3 
•    The values of RVP, even in the patients unaffected eyes, were significantly higher than in the eyes of controls (P < 0.001).3

 

As a clinician, you want to be able to detect high risk eyes. Performing ophthalmodynamometry will enable you to manage your patients more succesfully. 

 

1 Patients with diabetic retinopathy have high retinal venous pressure. Cybulska-Heinrich AK, et al. EPMA J. 2015 Feb 24;6(1):5
2 The effect of central retinal venous pressure in patients with central retinal vein occlusion and a high mean area of nonperfusion. McAllister IL, et al. Ophthalmology. 2014 Nov;121(11):2228-36
3 Retinal venous pressure in the non-affected eye of patients with retinal vein occlusions. Mozaffarieh M et al, Graefes Arch Clin Exp Ophthalmol. 2014 Oct;252(10):1569-71

 

Yes it can. 


Treatment with low-dose Nifedipine can decrease RVP in both eyes of glaucoma patients, particularly in those with the Flammer-Syndrome. This effect may be due to the partial inhibition of Endothelin-1 (ET-1) by Nifedipine.1

Other molecules with calcium channel blocking activity such as nimodipin and Magnesium can as well induce RVP lowering effect.


1 The effect of nifedipine on retinal venous pressure of glaucoma patients with the Flammer-Syndrome. Fang L et al. Graefes Arch Clin Exp Ophthalmol. 2015 Jun;253(6):935-9