4) Visual problems
The spectrum of visual disturbance due to hyper-viscosity of the blood is massive and ranges from blurring of vision to total blindness. Our retina is the main site for receiving visual signals, and it is highly susceptible to decreased oxygen levels, be it from a blood clot or from reduced delivery due to sluggish blood flow. The damage is usually reversible, but in prolonged conditions, visual loss can be permanent. Careful fundoscopic examination of the retina can lead the physician to suspect hyperviscosity.