My left eye is lower and rounded with a blunted cathus. Would canthoplasty fix this? (photos)

This can be a complex problem. Need personal evaluation to determine what should be done. It could be a canthal opening procedure or other.

Based on the pictures, it is hard to determine what is going on. An in person evaluation is needed for a proper assessment.

Hi there. I recommend you see a skilled oculoplastic surgeon for in person evaluation of your lower lid retraction and malformed canthal angle. The tissues need to be felt and further inspected to determine whether there is scar tissue pulling the lid down. This will inform what approach is most likely to improve your lower lid position should you wish to pursue a surgical intervention. Hope that helps.
Best,
Pradeep
Pradeep Mettu, MD
Oculofacial Plastic Surgery
Raleigh, NC

Hi and welcome to our forum!
The lateral canthal ligament is a band of fibrous tissue which extends from the tarsal plates of the eyelid to the lateral aspect of the zygoma of the orbit. It supports the lower eyelid and limits medial displacement of the lids when blinking. Trauma to the ligament can result in "round eye syndrome", where the lateral canthus lacks definition with blunting of the lateral palpebral angle. 
Treatment consists of a tarsotendinous reconstruction. I agree with the gameplan.
Best wishes...