Intrastromal corneal ring segments: effect of relationship between alignment and topographic keratometric meridians.
OBJECTIVE
To determine whether the keratometric and refractive surgical effects of paired intrastromal corneal ring segments (ICRS) depend on their alignment relative to steep and flat topographic meridians.


METHODS
St. Paul's Eye Unit, Royal Liverpool University Hospital, Liverpool, United Kingdom.


METHODS
Comparative case series.


METHODS
Keratoconic patients who had two 0.3 mm Intacs ICRS inserted were retrospectively grouped depending on alignment of segments within 30 degrees either side of the steep (meridional group) or the flat (perpendicular group) topographic meridians, respectively, with the rest in the oblique group. Principal outcome measures were changes in visual acuity, refractive surgical effect, and keratometric surgical effect 4 months postoperatively.


RESULTS
Forty eyes of 40 patients were included. There was a significant reduction in keratometric power (flattening) (P<.01) but not in refractive error in all 3 groups. The reduction in keratometric astigmatism was significantly greater in the perpendicular group (-2.67 diopters [D]) than in the meridional group (-0.65 D) (P=.03), with the oblique group (-0.9 D) in between (P=.12). The principal reduction was flattening orthogonal to the incision site, with relative steepening in the axis of ICRS alignment. In all groups, variations in the refractive surgical effect and keratometric surgical effect were very high.


CONCLUSIONS
Placement of two 0.3 mm ICRS had a variable effect with limited predictability. There was predominant flattening of the cornea orthogonal to the axis of ICRS alignment. Irrespective of the location of preoperative steep and flat keratometric meridians, the maximum reduction in astigmatism occurred when the incision and the segments were placed along the flat topographic meridian.


BACKGROUND
No author has a financial or proprietary interest in any material or method mentioned.
HM Stanley Hospital, St. Asaph, Liverpool, United Kingdom. lyndon.tu@ntlworld.com
Kyaw L
KL
Tu
Mark
M
Batterbury
Stephen B
SB
Kaye
D000328:Adult; D001251:Astigmatism / Q000503:physiopathology; D003319:Corneal Stroma / Q000503:physiopathology / Q000601:surgery*; D019781:Corneal Topography; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D019904:Polymethyl Methacrylate; D019736:Prostheses and Implants; D019919:Prosthesis Implantation / Q000379:methods; D012029:Refraction, Ocular / Q000502:physiology; D012030:Refractive Errors / Q000503:physiopathology; D012189:Retrospective Studies; D016896:Treatment Outcome; D014792:Visual Acuity / Q000502:physiology
D019904:Polymethyl Methacrylate