Effect of corneal curvature on optical zone decentration and its impact on astigmatism and higher-order aberrations in SMILE and LASIK.

PURPOSE: To determine the association between anterior corneal curvature and optical zone centration as well as its impact on aberration profiles in small-incision lenticule extraction (SMILE) and laser in situ keratomileusis (LASIK). METHODS: Seventy-eight eyes of 78 patients treated with SMILE (45 eyes) and LASIK (33 eyes) were included. The centration of the optical zone was evaluated on the instantaneous curvature difference map between the preoperative and 3-month postoperative scans using a superimposed set of concentric circles. The correlation between optical zone decentration and anterior keratometry values was evaluated. The effect of optical zone decentration on vector components of astigmatic correction and induction of higher-order aberrations (HOA) was assessed. RESULTS: The mean decentration distance was 0.21 ± 0.11 mm for SMILE and 0.20 ± 0.09 mm for LASIK (p = 0.808). There was a significant correlation between anterior keratometric astigmatism and decentration distance (r = 0.653, p < 0.001) for SMILE but not for LASIK (r = - 0.264, p = 0.138). Astigmatic correction was performed in 67 eyes. Optical zone decentration and the vector components of astigmatic correction were not correlated (p ≥ 0.420). Significant correlation was demonstrated between the decentration distance and the induced total coma (SMILE: r = 0.384, p = 0.009; LASIK: r = 0.553, p = 0.001) as well as the induced total HOA (SMILE: r = 0.498, p = 0.001; LASIK: r = 0.555, p = 0.001). CONCLUSION: Anterior cornea astigmatism affected the treatment centration in SMILE but not LASIK. Subclinical decentration was associated with the induction of total coma and total HOA, but it did not affect the lower-order astigmatic correction.

Using Retinal Imaging to Study Dementia.

The retina offers a unique "window" to study pathophysiological processes of dementia in the brain, as it is an extension of the central nervous system (CNS) and shares prominent similarities with the brain in terms of embryological origin, anatomical features and physiological properties.  The vascular and neuronal structure in the retina can now be visualized easily and non-invasively using retinal imaging techniques, including fundus photography and optical coherence tomography (OCT), and quantified semi-automatically using computer-assisted analysis programs. Studying the associations between vascular and neuronal changes in the retina and dementia could improve our understanding of dementia and, potentially, aid in diagnosis and risk assessment.  This protocol aims to describe a method of quantifying and analyzing retinal vasculature and neuronal structure, which are potentially associated with dementia. This protocol also provides examples of retinal changes in subjects with dementia, and discusses technical issues and current limitations of retinal imaging.