The effect of tunnel length and position on postoperative corneal astigmatism: An optical coherence tomographic study.

PURPOSE: The purpose of this study is to evaluate the effects of variation in tunnel length of same-sized clear corneal phacoemulsification incisions on the generation of surgically induced astigmatism and corneal astigmatism. METHODS: A total of 126 cataract patients treated in four study groups based on location and tunnel length of the clear corneal incisions (superior long, superior short, temporal long, temporal short) were reviewed. In the short tunnel groups, a 2.8 mm keratome was used with a motion parallel to the iris surface, while in the long tunnel groups, the same keratome was advanced in the corneal stroma until the mark on the keratome was reached. The surgically induced astigmatism and the corneal astigmatism were measured with corneal topography. The tunnel lengths were determined by anterior segment optical coherence tomography. RESULTS: The tunnel lengths of the long tunnel groups were significantly longer than the short tunnel groups. The total and anterior corneal surgically induced astigmatism of the superior long group was significantly higher than the other groups. Posterior corneal surgically induced astigmatism was similar. The postoperative total and anterior corneal astigmatism values of the superior long group was significantly higher than the other groups. No difference was observed for mean change in corneal astigmatism between the groups. CONCLUSION: The tunnel length of a clear corneal incision is a significant determinant of surgically induced astigmatism for superior placed corneal incisions. Therefore, for superiorly positioned clear corneal incision, the incision should be rectangular with a shorter tunnel to keep the surgically induced astigmatism to a minimum. For squarer-shaped clear corneal incision, limbal-temporal incisions may be performed for astigmatic neutrality.

Retinal vessel diameter obtained by optical coherence tomography is spared in Parkinson's disease.

PURPOSE: To define the alterations in retinal vessel diameter in Parkinson's disease (PD) by optical coherence tomography (OCT). METHODS: This is a case-control study including 41 eyes of 41 patients with diagnosis of PD and 35 eyes of 35 age- and sex-matched control subjects. All subjects underwent complete neurological and ophthalmological examinations before measurements. Retinal vessel diameters and peripapillary retinal nerve fiber layer (pRNFL) thicknesses were evaluated with spectral domain OCT (SD-OCT) with a circular scan centered at the optic disc. The diameters of the superior nasal and temporal arteries and veins, and inferior nasal and temporal arteries and veins were measured and then compared between the groups. Correlations with the duration of the disease, usage of levodopa, and pRNFL thicknesses between retinal vessel diameters were examined with Pearson and Spearman correlation analysis. RESULTS: Average pRNFL thickness is significantly decreased in PD compared to age- and sex-matched controls (p < 0.05). At all measurement points, retinal artery diameter measurements were decreased in the PD group compared to controls, but the differences did not reach statistical significance. Diameters of the retinal veins also did not show any significant difference in the PD and control groups. Superior temporal artery diameter was significantly decreased in patients using levodopa compared to nonusers (p = 0.022). There were no statistically significant correlations between pRNFL thicknesses or disease duration with retinal vessel diameters in PD group. CONCLUSIONS: Parkinson's disease does not seem to have an impact on the retinal vessel diameters obtained by SD-OCT.