11/08/2025
This 18 year old patient came in to examine his eyes today. I noticed that he has an abnormal head posture which he said he had it for many years (see images 1a, 1b). His symptoms were general exhaustion and coordination problems like difficulty in threading a needle. However, his myopia was very low, right eye -0.50/0, left eye -0.25/0. I suspect there has to be a more sinister problem than just myopia alone.
A cover test revealed that there is significant hypophoria of the right eye, which measured to 6Δ prism diopters (images 2a, 2b).
Unlike squints, phorias are latent (hidden) deviations of the eye, so the eyes appeared straight under normal circumstances. When covered, the problem right eye will deviate to its new position, in this case downwards.
Human tolerance to vertical phorias are poor. With such a substantial deviation of 6Δ prism diopters, binocular vision is difficult to achieve. This explains the lack of depth judgement in treading needles. His brain has to constantly coordinate the six extra-ocular muscles (image 3) to keep the eyes vertically levelled to maintain fusion. This excessive and consistent muscle contractions are exhausting and when the muscles cannot continue to contract further, the patient adopted an abnormal head posture to lessen the muscle contraction and exhaustion, as this allowed the 2 retinal images to be fused easier.
To treat his hypophoria, I prescribed prisms into his spectacles. How the prisms work in general has been described in other cases before (see images 4a, 4b). The prisms hugely reduced his exhaustion and lets see if his binocular vision can improve next year. Otherwise, some binocular vision exercises may be required. My job is done.... for the time being. 😃
(to be continued)
