Oct 2015 DOI 10.14302/issn.2470-0436.jos-14-571
SHIBA TakuyaCorresponding author
Department of Ophthalmology, Jikei University School of Medicine, Tokyo, Japan.
Purpose: To describe a new functional magnetic resonance imaging (fMRI) method for measuring the influence of regular astigmatism, both against-the-rule (ATR) and with-the-rule (WTR), on the human visual cortex. Setting: Department of Ophthalmology, Jikei University School of Medicine, Tokyo, Japan. Design: Experimental study. Methods: Images were acquired in two healthy volunteers using a 1.5 T scanner equipped for echo planar imaging. Horizontal and vertical sine wave grating flickering at a frequency of 8 Hz were simultaneously presented during the 20-second stimulation period. During the control period , subjects fixated on a control target. Stimulations were performed under three different conditions that included with hard contact lenses that were equal to emmetropia without astigmatism (condition 1); with hard contact lenses and cylindrical glasses of +6.00D at 0°, imitating WTR (condition 2); and with hard contact lenses and cylindrical glasses of +6. 00 D at 90°, imitating ATR (condition 3). Raw data were processed using in-house software with the significance of activation determined by Statistical Parametric Mapping (SPM 99). Results: Although higher activation was found in the primary visual cortex for condition 1 versus conditions 2 and 3, activation in the dorsal pathway was higher in conditions 2 and 3 compared to condition 1. Dorsal pathway activation was also higher in condition 3 versus condition 2. Conclusions: Study findings showed the potential influence of ATR and WTR on the human visual cortex , with fMRI able to detect the influence of regular astigmatism on the visual cortex. Our current results suggest that fMRI may be useful in exploring the influence of astigmatism on vision.
Jan 2015 DOI 10.14302/issn.2470-0436.jos-14-572
KavitaBhatnagarCorresponding author
Dr D Y Patil Medical College, Hospital & Research Center, Pune, India
Purpose: Cataract is the leading cause of blindness worldwide. Even in an uneventful cataract surgery, surgically induced astigmatism remains the major hurdle in attaining good unaided visual acuity post surgery. If pre-existing corneal astigmatism is not corrected at the time of surgery, it will result in more postoperative astigmatism; therefore, it is important to correct pre-existing corneal astigmatism. Material & Methods In this prospective study, 100 eyes of 100 age and sex matched patient’s with comparable preoperative astigmatism and visual acuity were divided in two groups according to pre operative corneal astigmatism. SIG (superior scleral incision group) included 50 eyes with steeper vertical axis and TIG (temporal corneal incision group) included 50 eyes with steeper horizontal axis. SIG and TIG were subjected to superior scleral tunnel and temporal corneal tunnel incisions respectively. Corneal astigmatism was measured preoperatively and at 1, 2 and 6 weeks postoperatively. Results: The mean postoperative astigmatism in SIG and TIG after 6 weeks was 0.545 ± 0.51D and 0.59 ± 0.48 D in comparison to preoperative astigmatism of 1.105 ± 0.54 D and 1.120 ± 0.49 D respectively. The difference was statistically significant in both the groups with P< 0.001 for both groups. The difference in surgically induced astigmatism between the two groups was not significant at any point of time after surgery (p>0.05). Conclusion: Incision site on steeper axis helps in reduction of pre-existing corneal astigmatism in cataract surgery. Both superior scleral and temporal corneal incisions help in neutralization of approx. 0.4-0.7 D of astigmatism.