cover uncover test in patients with vertical squint

this is a patient with vertical deviation, the following video is intended to help fifth-year medical students to understand cover uncover testing in the examination of squint.
This is the first patient that we’ll be examining today, he’s complaining of squinting in periods of visual inattention sometimes when he speaks to a person one of his eyes actually goes down and the other eye goes up so let’s try to examine the patient

let’s do quickly extraocular muscle movements this looks fine the other one is good ok so this is dextroversion looks fine as well to me, levoversion so the extraocular muscles look fine
so let’s do the cover uncover test now:

we put a cover in front of the right eye so putting up the cover will dissociate the single binocular vision which is hiding up phoria that the patient has so once I’ve put up the cover on the right eye the eye little bit drop down, so let’s take out the cover notice the corrective movement in the sound eye as you can see I’m putting up the cover on the right eye please notice the left eye it will just go up a little bit and then because of the binocular single vision that the patient has he will start to compensate for his mind hypophoria.
Let’s put the cover on the left eye till it goes up take it out so the patient’s problem is mainly in the left eye the patient has left hypertropia which is not accompanied by a right hypotropia as you can see here and there was no corrective movement here so it looks to me this is a DVD associated with vertical deviation

In order to examine this patient we need a prism we have to put the prism and the cover at the same eye since this type of squint doesn’t obey Hering's law so let’s look now whether we have some movement or not this is a 10 prism base down okay so the movement has disappeared completely and as you can see 10 prism base down makes up the whole trick once I removed from the prism it goes up a little bit and then goes down