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CASE REPORT: A solution for annoying residual astigmatism

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WC: corneal topography axial power maps

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Hugh Bradshaw

WC is a 42-year-old male physical education teacher with left monocular keratoconus. He was referred to me for a scleral contact lens fitting because he was unsuccessful wearing a corneal RGP lens due to comfort, particularly in a dusty environment.

Unaided visual acuity was R 6/5 L 6/15 and best corrected visual acuity was R +0.75/-1.00×55 6/4 and L plano/-3.00×155 6/9. WC found glasses unsuitable for his work. Corneal topography (Medmont E300, above) showed right subclinical (47.7 D) and left moderate (54.1 D) nipple cones.

To improve comfort the first lens design trialled was a 16.5 mm KATT3 scleral lens:

KATT3 lens trial 7.50/16.5/-2.75 tan 50/45S

Central clearance 280 µm

Over refraction +4.75/-2.00×90 6/6

This lens was extremely comfortable but with two dioptres of residual astigmatism, the visual acuity with a spherical lens did not improve unaided vision.

The second lens design trialled was a 13.5 mm Epicon lens:

Epicon LC lens trial 7.00/13.5/-8.00 E periphery

Edge too tight

Over refraction +6.50/-1.75×87 6/5

This lens was a compromise in comfort but an improvement on his previous corneal RGP lens.

At this stage a 10.5 mm corneal RGP lens was trialled to assess whether the residual astigmatism could be eliminated with an aspheric rotationally symmetrical lens. This residual astigmatism remained so I discussed the options available: a spherical scleral lens with over-glasses or a toric scleral or corneo-scleral lens. The patient did not think having over-glasses would be an improvement on his current situation.

Toric or rotationally asymmetrical scleral lenses are possible to manufacture but in practice, lens location and stability are a problem. A prism ballast design improves stability but the lens edge thickness can increase to up to 800 µm, affecting the lens fit and comfort, and can cause increased corneal and limbal hypoxia. Corneal and corneo-scleral lenses locate better with more stability in a ballast front surface toric design.

After considering the options available, a 13.5 mm Epicon front surface toric lens was ordered:

Epicon LC Toric 6.8/13.5/-2.50/-1.50×87 F periphery

Visual acuity with this lens was 6/5 and the patient was very happy with vision and comfort wearing the lens. The rotational stability of this lens was excellent.

Residual astigmatism can be an annoying complicating factor in contact lens fitting. In this case, both excellent comfort and vision were required to achieve a successful lens fitting. Epicon toric lenses can provide excellent comfort and visual stability when residual astigmatism is a problem, particularly in monocular keratoconus.



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