Thanks for the additional information. It is helpful. I don't want to rule out the start of clouding of the eye since it may just be starting. Clouding of the eye isn't just caused by cataracts though the breed can be prone to juvenille cataracts. It can also be caused by corneal ulceration and injury to the eye.
A corneal ulcer may be caused by injury, eyelashes, scratching the eye and has similar symptoms to those of glaucoma and anterior uveitis. This is a very good possibility given the breed of your dog which I will go over in more detail. The third eyelid frequently covers the eye so sometimes the eye is not able to be seen with a corneal ulceration. You can read about this here:
You can read up on Cataracts here:
The following site goes over reasons for cloudiness of the eye just in case it develops..
Shih Tzus as a breed have shallow eye sockets. They are prone to eye problems such as not being able to close their eyelid over the cornea of the eye (lagophthalmos ). Due to this problem they have the tendency to develop an inflammation of the cornea (Keratitis) which can become ulcerative in its severest form. This can lead to scaring that can decrease vision. In addition, due to they way the eye socket is, the eyelid can clamp behind the eyeball cutting off oxygen to the retina which can lead to blindness if not treated immediately. This is called proptosis.
They also can have problems with dry eye and their eyelashes irritating the eyeball and possibly causing chronic corneal irritation. These conditions are Distichiasis and Ectopic Cilia. They also can have hereditary cataract or juvenile cataracts and PRA which leads to blindness. Dogs can also develop a luxating lens as well.
That clear spot you describe could be a corneal ulcer and the lazy eye movement you describe be a pain reaction. We do see some rolling of the eyes in reaction to eye pain. Dogs are not like people and they try to not show their pain at all. As you have seen, this could be an emergency situation depending on the severity of the condition. Given that your breed is prone to a lot of eye issues, I would have Max seen as soon as possible.
I hope this information is helpful to you and you are satisfied with my response. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have.