Myopia is short sightedness, hyperopia is long sightedness and diplopia is double vision, so what is polyopia? Polyopia is seeing more than one image, typically more than two (otherwise would just be classified as diplopia). It can be ocular, ie caused by a problem in the eyes so problem can be partially resolved by closing one eye or cerebral, caused by problem in brain.
I saw a lovely lady, aged 44, earlier in the week who had cerebral polyopia after having a stroke 14 years ago. If you looked at her eyes there was nothing wrong with them, normal discs, healthy maculae, clear media, everything was as it should be. Retinsocopy showed a minimal prescription of +0.25/-0.50x180 RE and +0.50/-0.50x180 LE so nothing significant there either. However the patient's vision and VA were 6/120 right, left and binocular and that was at a push. The problem was as the patient described it "I can see 24 images, 12 from right eye, 12 from left eye and they are all moving". So the problem wasn't that the eyes couldn't see, it was that the patient was seeing multiple moving copies of the image and wasn't sure which one was real. So the real test wasn't what could I do to improve the patient's sight, it was what I could do to reduce all the dancing images.
As the vision was poor, conventional methods of binocular vision assessment such as Maddox rod, Mallett fixation disparity won't work so it was purely subjective as to what felt best for the patient. As the issue was cerebral it wasn't as simple as just trying prism in one eye and then splitting for cosmesis, I needed to do each eye separately, and with no guide it was just purely a case of putting prism in different directions and finding out if patient found it was better or worse. In the end we found that 9 prism dioptre base in RE and 4 prism dioptre base in LE seemed to pretty much stop the movement in both eyes, which patient was amazed by and really pleased with.
Next up was reading, with any low vision patient this is always a compromise between clarity and comfort for working distance. Starting with +4.00 add we found this wasn't enough magnification for what the patient wanted so we starting increasing it. At the end we found a +12.00 add worked best for the patient which then meant we needed to increase the prism to help with the eyes converge.
The final problem is frame selection and getting some lenses to look good, but in my store that's for the dispensing team so I took my leave and left patient with our dispensing optician.