One of my patients, a 7-year-old girl, has had eye examinations every year since she was 4 years old. She has always had a slight right upper lid ptosis since she was born according to her parents. There have never been any other neurological signs, the cosmesis has been reasonable and it has become less noticeable as she has grown older. She has never had any refractive error in the past and has always managed at least 6/6 in each eye. Today she has 6/12 vision in the right eye and 1.50 DC with the rule astigmatism in the right eye which when corrected gives 6/6. There is no refractive error in the left eye. Why has she developed monocular with-the-rule astigmatism?

With-the-rule astigmatism means that the cornea is steeper in the vertical meridian than the horizontal. The analogy is a barrel lying on its side. I often use this analogy with parents instead of talking about rugby balls as everyone can picture a barrel but not everyone knows what a rugby ball looks like.

The ptosis is interesting. It sounds like it has been caused by aponeurotic disinsertion. There is a thinning and disinsertion of the levator aponeurosis. The aponeurosis is a sheet of pearly-white fibrous tissue that takes the place of a tendon in flat muscles having a wide area of attachment. This fibrous membrane covers certain muscles or connects them to their origins or insertions. The fibrous membrane which connects the levator muscle in the upper eyelid becomes thin and/or disconnected from its origin. This results in a reduction in the strength of the muscle and the upper lid droops. This may have been caused by a subtle development anomaly at the embryo stage or during birth.

The astigmatism is very likely to have been caused by the pressure of ptotic lid on the cornea, deforming it by pushing the cornea in and causing it to be steeper in the vertical meridian. The distortion and astigmatism cause a miss focus in the eye and this has led to the reduction in vision. It is good that the vision improves to 6/6 with refractive correction as this indicates there is no amblyopia.

The reduction in vision in the right eye may impact on the vision with both eyes open and this may make it difficult for the child to see things on the board at school. Amblyopia is not a danger in this case.

The question is whether to refer for lid surgery or to correct the refractive error or both. My opinion is to provide glasses for learning activities and at the same time to seek an opinion from an eye specialist with experience in lid surgery. It may not be appropriate to conduct lid surgery at this point but the surgeon can monitor the lid position and look out for an increase in the ptosis. You can monitor the visual acuity and astigmatism and increase the correction if it worsens and let the surgeon know.

On the surface, this sounds like a simple case of monocular refractive error correction but it is more complicated than that.

 

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