This article is more than 5 years old. Information may no longer be current.
Opposite clear corneal incisions with cataract surgery improve pre-existing astigmatism
Incisions made along the superior-inferior meridian cut more collagen fibrils perpendicularly, causing a greater refractive effect.
Click Here to Manage Email Alerts
Paired opposite clear corneal incisions may have a significantly greater refractive effect and more stable surgically induced astigmatism for with-the-rule astigmatism correction compared with against-the-rule astigmatism correction, according to a study.
Opposite clear corneal incisions (OCCIs) are one of a few options used to improve pre-existing astigmatism at the time of cataract surgery; however, there are varying reports on mean astigmatic correction, incision size and follow-up time.
“Cataract operation presents the ideal opportunity to reduce or eliminate mild to moderate corneal astigmatism in routine patients,” lead investigator Patrick J. Chiam, FRCOphth, MBA, told Ocular Surgery News. “OCCI is an ideal way of doing so without much additional time or cost. By understanding the refractive effect of OCCI with time, surgeons are able to make this procedure more predictable. It is likely to reduce patient spectacle dependence and provide higher visual satisfaction.”
Steepest meridian and keratome width
In the retrospective cohort study, 84 consecutive eyes with keratometric astigmatism of 1.5 D to 2.5 D were separated into three groups with varying steep meridians and keratome widths.
To analyze OCCIs on with-the-rule (WTR) astigmatism correction, group A had the steepest meridian at 90° ± 20°, and to analyze OCCIs on against-the-rule (ATR) astigmatism correction, groups B and C had the steepest meridian at 180° ± 20°.
The keratome width was 3.2 mm for groups A and B and 3.5 mm for group C.
Corneal astigmatism and visual acuity
Median magnitude of surgically induced astigmatism was 1.9 D for all three groups preoperatively. At 1 month postoperatively, the magnitude was reduced to 1.7 D for groups A and C and significantly reduced to 1.1 D for group B. At 6 months postoperatively, the magnitude was reduced to 1.6 D for group A and 1.5 D for group C and significantly reduced to 0.8 D for group B.
When using the same width keratome, OCCIs had a greater effect on WTR astigmatism compared with ATR astigmatism. Chiam attributed this to the orientation of the cornea collagen, which influences the number of fibers incised during OCCIs.
“In short, the fibers transverse the cornea in a superior-inferior and nasal-temporal direction, but start to curve acutely to form the circumcorneal annulus at different distances from the limbus,” he said. “As paired OCCIs are made at the same distance from the limbus, incisions made along the superior-inferior meridian cut more collagen fibrils perpendicularly, causing a greater refractive effect.”
At 1 month postoperatively, groups A and C had a median uncorrected distance visual acuity of 0.1 logMAR vs. 0.3 logMAR for group B. At 6 months postoperatively, uncorrected distance visual acuity in groups A and C remained better than group B, at 0.2 logMAR for groups A and C and 0.3 logMAR for group B.
Ease of OCCIs
OCCIs are not difficult to perform, and the skill can be acquired easily, Chiam said.
“It’s easier to perform compared to limbal relaxing incision, which requires additional instrument,” he said. “It’s far cheaper than refractive laser or toric intraocular implant to correct mild to moderate corneal astigmatism.”
Surgeons must ensure the incisions are self-healing because an extra surgical incision may potentially act as an additional conduit for intraocular infection and resultant endophthalmitis.
Awareness of this procedure and continuation of further studies are the next steps in making OCCIs a norm in astigmatism correction, Chiam said.
“Surgeons should be aware of such an option, especially because it is not difficult to perform and does not require much additional time and little or no extra surgical instrument,” he said. “What is likely to make this procedure more receptive is a more comprehensive nomogram for different types of astigmatism for different age groups.” – by Kristie L. Kahl
- Reference:
- Chiam PJ. Cornea. 2015;doi:10.1097/ICO.0000000000000441.
- For more information:
- Patrick J. Chiam, FRCOphth, MBA, senior glaucoma fellow, can be reached at Birmingham and Midland Eye Centre, City Hospital, Dudley Road, Birmingham, B18 7QH, United Kingdom; email: pjtchiam@yahoo.com.
Disclosure: Chiam reports no relevant financial disclosures.