Myopes considering refractive surgery are advised that surgically correcting their nearsightedness may be a disadvantage after age forty, when the eyes become presbyopic and lose their ability to accommodate or change focus, because they will then need to use glasses for reading. Myopes with low astigmatism find near vision better, though not perfect, without glasses or contact lenses when presbyopia sets in, but the more astigmatism, the poorer the uncorrected near vision.A surgical technique offered is to create a "reading eye" and a "distance vision eye", a technique commonly used in contact lens practice, known as monovision. Monovision can be created with contact lenses, so candidates for this procedure can determine if they are prepared to have their corneas reshaped by surgery to cause this effect permanently. Mechanism
The cause of presbyopia is lens hardening by decreasing levels of α-crystallin, a process which may be sped up by higher temperatures. It results in a near point greater than 25 cm (or equivalently, less than 4 diopters). In optics, the closest point at which an object can be brought into focus by the eye is called the eyes near point. A standard near point distance of 25 cm is typically assumed in the design of optical instruments, and in characterizing optical devices such as magnifying glasses.There is some confusion over how the focusing mechanism of the eye works. In the 1977 book, Eye and Brain, for example, the lens is said to be suspended by a membrane, the zonula, which holds it under tension.
As with other types of intracranial hematomas, the blood almost always must be removed surgically to reduce the pressure on the brain. The hematoma is evacuated through a burr hole or craniotomy. If transfer to a facility with neurosurgery is unavailable, prolonged trephination (drilling a hole into the skull) may be performed in the emergency department. Large hematomas and blood clots may require an open craniotomy.Medications may be given after surgery. They may include antiseizure medications and hyperosmotic agents to reduce brain swelling and intracranial pressure.It is extremely rare to not require surgery. If the volume of the epidural hematoma is less than 30 mL, the clot diameter less than 15 mm, a Glasgow Coma Score above 8, and no visible neurological symptoms, then it may be possible to treat it conservatively. A CT scan should be performed, and watchful waiting should be done, as the hematoma may suddenly expand. Prognosis
The prognosis is better if there was a lucid interval than if the person was comatose from the time of injury. Arterial epidural hematomas usually progress rapidly. However, venous epidural hematomas, caused by a dural sinus tear, are slower.Outcomes are worse if there is more than 50 mL of blood in the hematoma before surgery. Age, pupil abnormalities, and Glasgow Coma Scale score on arrival to the emergency department also influence the prognosis.