How best to treat cataracts in horses

A cataract in a horse is a serious condition of the lens of the eye, where an opacity or a cloudy patch can affect one or both eyes, reducing the quantity of light rays that reach onto the back of the eye.
This condition can be present in foals, in which case they are known as congenital cataracts – this will be checked for during a routine post foaling exam – or they can develop secondary to trauma or other ocular conditions. 
One of these conditions includes equine recurrent uveitis, where repeated inflammation inside the eye can lead to cataracts as well as other clinical ocular findings. In some breeds the condition can also be heritable, for example in Morgan horses.
Diagnosis is by ocular examination looking through the eye with an ophthalmoscope from a distance, as well as from up close. The use of tropicamide can also help to dilate or widen the pupil to get better visualisation of more peripheral lesions and, occasionally, they can also be detected on an ultrasound examination of the eye if the cataract’s is particularly large or dense.
Cataracts can vary in their position and appearance within the lens. They can be present in the front (anterior) or back (posterior) of the lens, in the centre or the periphery or it can affect the entirety of the lens (generalised). 
The condition may be described by their exact location within the lens – polar, subcapsular, lamellar, perinuclear, nuclear, equatorial or cortical – or their state of progression, for example incipient, immature, mature or hypermature and if they are in the centre they are most likely to be within the visual axis and if to the side/periphery then less likely to be within the visual axis. 
Cataracts can be well circumscribed in which case they often look like a mark in an otherwise clear lens or it can affect a larger area giving a blurry appearance and the size and location will determine the likelihood of how the cataracts could be potentially affecting the horse's functional vision.
If a cataract has developed gradually over time then the owner may not have noticed any clinical signs, however, if clinical signs are present they could include becoming more spooky on one side, turning the head when ridden or altered head carriage, stumbling, walking into objects, increased facial injuries or noticing a cloudy appearance to the eye.  
They are also one of the conditions that are checked for during a pre-purchase exam. The majority do not progress, however, some can be difficult to predict and often the only way is to monitor and re-check the cataracts after a 6-12 month period. It should also be noted that the presence of a cataract may affect future sales should the purchaser decide to sell the horse on further down the line.
Treatment of the disease may or may not be required depending on the size, appearance and location and if there is any underlying or concurrent condition and if an underlying condition such as uveitis is present, then getting this condition under control would be required. 
If the cataracts is not within the visual axis and is otherwise small and well circumscribed then no treatment would likely be necessary. If the cataracts is large or generalised and affecting the vision with no concurrent disease then it may be a candidate for surgery and lens replacement, known as phacoemulsifcation, which is performed under general anaesthesia by veterinary and ophthalmology specialists. It involves making an incision through the cornea and lens capsule before a specialised instrument removes the lens contents and then replacing with an artificial lens.