Sweety Sharma, B.Optom
Senior Clinical Optometrist, Dr. Shroff’s Charity Eye Hospital, New Delhi, India
Glaucoma, the alternate worldwide leading cause of blindness(1), is a progressive and habitual visual objection characterised by the degeneration of the retinal ganglion cell and its axon with corresponding visual field disfigurement. (2)
Intra-ocular pressure (IOP) is a known malleable trouble factor for glaucoma. Thus, the idea of glaucoma operation is to lower the IOP to achieve a safe target pressure. Still, glaucomatous damage occurs in some cases despite a significant reduction of IOP. Ocular perfusion pressure (OPP) is the pressure at which blood gets into the eye and is defined as the deviation between the arterial pressure and the venous pressures within the eye. IOP can be used instead of venous pressure when assessing OPP since venous pressure in the eye approximates the IOP.
Several studies interlaced vascular threat factors in the pathogenesis of glaucoma, blood pressure (BP) and ocular perfusion pressure (OPP) being the most studied. This vascular thesis is grounded on the premise that irregular perfusion and the posterior ischemia of the optic nerve head (ONH) execute a major part in glaucomatous damage.
Specifically, mean OPP is calculated as two-thirds of the systemic mean arterial pressure (MAP) minus the IOP. Increasing MAP by two-thirds here accounts for the specific pressure difference between the brachial and ophthalmic artery in the upright orientation.
Mean OPP = 2/3 MAP- IOP
MAP = DBP + [1/3 X (SBP – DBP)]
*OPP- Ocular Perfusion Pressure, MAP- Mean Arterial Pressure, IOP- IntraOcular Pressure, DBP- Diastolic Blood Pressure,SBP- Systolic Blood Pressure
Systolic OPP (SOPP) elucidates the dissimilarity between systolic blood pressure (BP) and the IOP, and the diastolic OPP (DOPP) is defined as the gap between diastolic BP and IOP. The conservation of ocular perfusion pressure depends on a complex regulation process that balances BP and IOP to ensure respectable irrigation of ocular tissues. Abnormal perfusion occurs when this process is altered due to vascular dysregulation, which has been proposed as an underpinning cause for glaucoma damage.(4-6)
Population-grounded epidemiological studies set up strong interrelations between low ocular perfusion pressure and open-angle glaucoma (OAG) frequency, as well as OAG prevalence. A drop in perfusion pressure may significantly drop the optic blood flux in the absence of vascular autoregulation.(7,8)
Recent epidemiologic studies and clinical trials noted that low ocular perfusion pressure was significantly related to open-angle glaucoma (OAG). It is also reported that glaucoma is more than just a complaint of a single type of increase in pressure (IOP) and that some analysis of OPP also needs to be considered when determining an existence’s trouble of evolving glaucoma or passing complaint progression.
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