Lens luxation is correct!
An aphakic crescent is present when the margins of the lens can be seen in the pupillary zone. This is almost always a sign of either lens luxation or subluxation. In this case, the lens was subluxated and displaced anteriorly. Because the lens is not fully luxated yet (in which case it becomes a surgical emergency), the owner can be advised to monitor the dog carefully for progression of the disease, which would often induce signs of ocular discomfort. However, this is not always obvious for the owner (especially with posterior luxation), and lens luxation can rapidly cause inflammation and glaucoma, both of which may lead to vision loss. Alternatively, if the owner does not want to take that risk, the subluxated lens can be removed, with or without implantation of a synthetic intraocular lens. In my opinion, this is the ideal option if there is evidence that the lens subluxation will progress. In this case, the dog was a terrier (a predisposed breed) that had already lost one eye from lens luxation and glaucoma, and the owner elected for lens removal before complete luxation.