People who receive multifocal lenses will experience variable degrees of halo or glare symptoms in bright light or when driving at night. Their contrast sensitivity may also initially be diminished. Doctors have known for many years that these symptoms typically improve over 1-6 months after surgery with most people settling into excellent vision with minimal glare or halo issues. This has always been thought to be due to changes in the visual cortex in the brain which adapts to the new vision from the multifocal lenses. Doctors have explained this to patients as a process of neural-adaptation.
Now a study using functional MRI finally confirms that actual changes in activity levels in the brain occur after multifocal lens implantation. The study performed F-MRI on people before surgery and then 3 weeks and 6 months after. At 3 weeks after lens implantation the visual cortex was seen to be working hard to process vision and this correlated well with reported symptoms by patients. By 6 months the level of visual cortex activity has returned to pre-surgical levels and this matched well with the improvement and resolution of reported symptoms.
In other words the neural networks in the visual cortex of the brain adapts to provide optimal vision!
Rosa AM, Miranda ÂC, Patrício MM, McAlinden C, Silva FL, Castelo-Branco M,
Murta JN. Functional magnetic resonance imaging to assess neuroadaptation to
multifocal intraocular lenses. J Cataract Refract Surg. 2017
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