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The analysis of ocular astigmatism not originated from cornea and lens
Session Title: Assessment of Astigmatism
Session Date/Time: Saturday 05/10/2013 | 11:00-12:30
Paper Time: 12:10
Venue: Main Lecture Hall (Ground Floor)
First Author: : K.Uchiyama JAPAN
Co Author(s): : N. Kato C. Sakai
Toric intraocular lens implantation is usually effective to correct regular astigmatism caused by the cornea. However, there could be very unusual cases revealing postoperative residual astigmatism that could not be corrected by toric IOL implantation. We reported a representative case with such residual astigmatism after toric IOL implantation in 2012 ESCRS meeting, and suspected that residual astigmatism might originate from the retina or other parts of the eye excluding the cornea or lens. To prove this hypothesis, we assessed ocular astigmatism in aphakic state during cataract surgery in the present investigation.
The Department of Ophthalmology, Kanazawa Red Cross Hospital.
Twelve eyes of 7 patients (age 72.4 ± 5.2 year-old; 4 males and 3 females) with cataract were enrolled. Patients with disorders or conditions that could affect to refractive/keratometric assessment, such as severe corneal epithelitis, keratoconus, corneal scars, diabetic maculopathy, or other macular diseases, were excluded. The eyes that implanted toric IOLs were also excluded. They underwent cataract extraction and intraocular lens implantation by phacoemulsification and aspiration technique through the temporal corneal incision of 2.4mm in width. After phacoemulsification and aspiration, the anterior chamber and the lens capsule were filled with BSS-plus® (Alcon Japan, Tokyo, Japan), and refractive error was measured by a portable refractometer (ARK-30, NIDEK, Aichi, Japan) prior to the intraocular lens implantation. Astigmatism caused by internal eye except the cornea and the lens (aphakic internal astigmatism) was calculated by subtracting postoperative keratmetric astigmatism from the intraoperatively-measured total astigmatism in aphakic state. Postoperative examination including measurement of keratometric readings and manifest refraction were performed at 1 week after the surgery. Correlation between astigmatism caused by internal eye and postoperative residual astigmatism was analyzed using the Spearman"s rank correlation．
The intraoperatively measured total astigmatism was 0.844 ± 0.337D (0.25D to 1.47D). Aphakic internal astigmatism was 0.864 ± 0.452D (0.25D to 1.65D), but was neither correlated with postoperative cylindrical errors measured by refractometer (-0.854 ± 0.458D; p＝0.9033) nor manifest cylindrical power (-0.438 ± 0.402D; p=0.8413). However, 2 cases revealed greater aphakic internal astigmatism out of mean±2SD, 1.56D and 1.65D, respectively, and those 2 cases showed greater postoperative manifest cylindrical power (-1.00D and -1.25D, respectively).
The present results may indicate that the existence of internal astigmatism originated from unknown factors other than the cornea and the lens. Intraoperative measurement of refractive error may be usuful to detect rare cases with such internal astigmatism and may help to prevent postoperative residual astigmatism.