Monovision and Blended Vision
Monovision is one of the most commonly used strategies to reduce spectacle dependence for people with presbyopia, who need glasses for reading and / or separate glasses for distance.
Monovision is where one eye (usually your dominant eye) is corrected for good distance vision, and the other is corrected for near or intermediate vision. This can be achieved with:
In traditional monovision, a large difference between the eyes was created. This provided good vision at distance and near, but left a large "blur zone" in the intermediate range of vision. This meant people often struggled to cope with the difference and felt their vision with both eyes open was uncomfortable.
As a result, so-called “modest” monovision is now preferred. There is good scientific evidence that a difference of around 1.25 to 1.50 dioptres between each eye is the optimum target (read more here). This provides an excellent level of spectacle freedom, while minimising any problems related to the eyes being unbalanced. It is likely that you will still need a weak pair of reading glasses for some tasks, such as reading small print or in dimly lit areas (imagine reading a menu in a cosy restaurant). For most other daily activities , you should find that you can do without glasses.
Blended vision is a further refinement of this, whereby modest monovision is enhanced with additional control of spherical aberration, to replace the "blur zone" with a more functional "blend zone".
As with all refractive surgery, achieving a precise outcome is crucial. I have worked with Professor Graham Barrett (Australia) and Dr Warren Hill (USA), global experts in the subject, to investigate how outcomes of monovision can be optimised. If you are interested, you can read about our research here.
An advantage of monovision is that the visual quality in each eye is maximised. Unlike with multifocal or extended depth of focus lenses, the risk of troublesome visual disturbances such as halos around lights is minimal.
With monovision, both eyes see slightly differently. If you were to close each eye in turn, you will notice a difference. Your distance eye will not see clearly for near, and your near eye will not see clearly for distance. However, with careful planning and a bit of time, the brain learns to use both eyes together as usual. It is best to avoid comparing each eye, as this will just delay your brain’s adaptation process.
"Will I be spectacle free with monovision or blended vision?"
Complete freedom from glasses can never be guaranteed with any refractive procedure.
With monovision and blended vision, it is likely that you will be spectacle free for most things in normal day-to-day life.
Some people may still prefer to put on reading glasses for some specific tasks, such as reading small print for an extended period of time or in low lighting conditions.