occlusion of the central artery
acute occlusion of the blood vessel supplying the entire retina which causes a sudden painless loss of sight of the affected eye. A sensible treatment is possible only within the first hours after the occurrence of the problem. Emergency!

occlusion of the central vein
occlusion of the central retinal vein, which can cause a rapid deterioration of vision up to the loss of sight; severe late complications may lead to the loss of the eye. Emergency!

occlusion of a venous branch
occlusion of a retinal vein with a more or less distinct disturbance of the circulation in the affected retinal region. An ophthalmological clarification is absolutely necessary!

orbital fat prolapse
the moving forward of the fat tissue filling the eye orbit, which is caused by tissue flaccidity; it mostly occurs at an advanced age and is accompanied by the formation of unsightly bulgings especially in the region of the lower lids (»lacrimal sacs«).


photodynamic therapy (PDT)
new, major procedure for the treatment of the exudative macular degeneration: the drug Verteporfin, which is administered intravenously, is activated by a laser beam and brings about a sealing of the porous blood vessels in the region of greatest visual acuity.

photoreceptors
sensory cells of the retina; the density of the photoreceptors increases from the periphery to the centre of the retina. The region of greatest visual acuity (macula) has the highest density of photoreceptors and, for this reason, the highest resolution capacity.

phototherapeutical keratectomy (PTK)
modern procedure for the treatment of a recurrent corneal erosion: in the diseased region, the cornea is modified with the excimer laser in a way that a lasting connection between the superficial and the deeper corneal layers can be formed again and a final healing of the wound sets in.

ptosis
»droopy eyelid«; drooping of the upper eyelid due to a deteriorating functioning of the eyelid levator muscle; it is mostly the consequence of age-related tissue flaccidity, rarely caused by neurological or muscular problems.