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B. L. Tannen, K. L. Fry, P. S. Hersh; Topographic Changes Relative to the Placement of One versus Two Intra-Stromal Corneal Ring Segments in Patients With Keratoconus. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4331.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate topographic changes relative to the placement of one versus two intra-stromal corneal ring segments (Intacs) in patients with keratoconus.
Corneal topography (EyeSys) was reviewed in 9 eyes of 7 patients with keratoconus who had Intacs surgery. Channels were created using the Intralase femtosecond laser and either one (Single) or two (Double) 0.35mm Intacs were placed. The incision was placed at the steep axis. An overlay to the topographic Difference Map was created to collect changes in corneal power centrally and at two rings of 12 spots placed 30 degrees apart at 3mm and 5mm optical zones (oz). The overlay was then aligned with the axis of incision to collect data relative to the placement of the Intacs.
Four eyes had a Single and five eyes had Double Intacs placed. Mean age was 32.3 yrs (Single) and 28.0 yrs (Double) (range 23-40 yrs). Mean follow up was 67.6 days (Single), and 59.0 days (Double). Pre- and post-op mean UCVA was 20/100 (Single) and 20/606 (Double), and 20/54(Single) and 20/139 (Double) respectively. Pre- and post-op mean BCVA was 20/25 (Single) and 20/48 (Double), and 20/23 (Single) and 20/38 (Double) respectively.More corneal flattening occurred at the 5mm oz than at the 3mm oz for both Single and Double Intacs (Single mean change = -0.8D at 5mm and +1.0D at 3mm; Double mean change = -3.2D at 5mm and -1.1D at 3mm). Single Intacs caused a central corneal steepening, while Double Intacs caused a central corneal flattening (Single mean central change = +2.5D; Double mean central change = -2.8D). Single Intacs caused more flattening in the inferior meridians adjacent to its placement compared to the superior meridians opposite its placement (Inferior change =-2.2D at 5mm and +1.1D at 3mm; Superior change =+0.9D at 5mm and +1.5D at 3mm). Double Intacs caused more flattening in the meridians adjacent to the superiorly placed Intacs compared to the meridians adjacent to the inferiorly placed Intacs (Superior change =-4.1D at 5mm and -1.6D at 3mm; Inferior change=-2.0 at 5mm and 0.0D at 3mm).
Topographic changes in this small sample suggest that different effects occur in different regions of the cornea relative to the placement of Single and Double Intacs that may be useful in surgical planning, although similar improvements in UCVA and BCVA occurred in both groups.
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