Never thought of it deeply before (although reading toxicology stuff on it it does seem to be pretty lethal), but yes, irreversible blindness could potentially happen from high doses or long-term use of chloroquine. It damages your retinas. Wikipedia has an ok article about 'chloroquine retinopathy'. It seems what typically happens is it messes up your heart a bit.
I searched for papers about this and it seems it's very fatal and fast at high doses, but that they can treat the poisoning*, so you would definitely not want to be interrupted. I couldn't find much about long-term effects, as chloroquine toxicity has generally been researched in the context of whether you can resuscitate the person or not. But I also feel like blindness might have been mentioned a bit more? So while it's obviously a possibility at these doses (and also kinda hard to research since at high doses people just die), most information about it is about it as a risk of cumulative use.
*
https://link.springer.com/referenceworkentry/10.1007/978-3-319-20790-2_99-1 (there are also older sources on this, and the citations could be useful - I see other case studies listed)
*
https://lifeinthefastlane.com/tox-library/toxicant/anti-malarial/chloroquine-and-hydroxychloroquine/
*
https://toxnet.nlm.nih.gov/cgi-bin/sis/search2/r?dbs+hsdb:@term+@rn+@rel+54-05-7
*
http://curriculum.toxicology.wikispaces.net/Chloroquine
*
http://eyewiki.aao.org/Hydroxychloroquine_toxicity
The toxnet source has specific info on this, as does eyewiki -
'Retinopathy is considered to occur when the total cumulative dose ingested exceeds 100 g. Blurring of vision, diplopia may occur with short-term chloroquine therapy and are reversible.' (from the toxnet source) I would not use this as a guarantee, but there was a whole paragraph on this
In all fairness, most suicide attempts have nasty suicide effects if you fail and get resuscitated, often brain damage from oxygen deprivation etc. or organ damage from toxicity, so it's up to you how to evaluate these things and how much you value reliability (I personally value it very highly).
I would consider this if chloroquine were particularly accessible to me, though - the main concerns are as with any other drug overdose, being able to take it without vomiting or passing out first, and making sure it's painless. It's not readily available here, so no particular reason to consider it.
