Question:
How can the pterygium result in decrease vision in this case?
Answer:
Although pterygia affecting the visual axis can result in decrease vision especially in scotopic conditions due to dilation of the pupil. In addition to physically affecting visual axis pterygia can induce astigmatism.
In this case there is an astigmatism of 4.5D (denoted by red arrow). There is significant flattening of the ocular surface (denoted by red *)
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