Relationship Between Retinal Layer Thickness and Genetic Susceptibility to Age-Related Macular Degeneration in Asian Populations

Purpose: For OCT retinal thickness measurements to be used as a prodromal age-related macular degeneration (AMD) risk marker, the 3-dimensional (3D) topographic variation of the relationship between genetic susceptibility to AMD and retinal thickness needs to be assessed. We aimed to evaluate individual retinal layer thickness changes and topography at the macula that are associated with AMD genetic susceptibility. Design: Genetic association study. Participants: A total of 1579 healthy participants (782 Chinese, 353 Malays, and 444 Indians) from the multiethnic Singapore Epidemiology of Eye Diseases study were included. Methods: Spectral-domain OCT and automatic segmentation of individual retinal layers were performed to produce 10 retinal layer thickness measurements at each ETDRS subfield, producing 3D topographic information. Age-related macular degeneration genetic susceptibility was represented via single nucleotide polymorphisms (SNPs) and aggregated via whole genome (overall) and pathway-specific age-related macular degeneration polygenic risk score (PRSAMD). Main Outcome Measures: Associations of individual SNPs, overall PRSAMD, and pathway-specific PRSAMD with retinal thickness were analyzed by individual retinal layer and ETDRS subfield. Results: CFH rs10922109, ARMS2-HTRA1 rs3750846, and LIPC rs2043085 were the top AMD susceptibility SNPs associated with retinal thickness of individual layers (P < 1.67 × 10−3), all at the central subfield. The overall PRSAMD was most associated with thinner L9 (outer segment photoreceptor/retinal pigment epithelium complex) thickness at the central subfield (β = −0.63 μm; P = 5.45 × 10−9). Pathway-specific PRSAMD for the complement cascade (β = −0.53 μm; P = 9.42 × 10−7) and lipoprotein metabolism (β = −0.05 μm; P = 0.0061) were associated with thinner photoreceptor layers (L9 and L7 [photoreceptor inner/outer segments], respectively) at the central subfield. The mean PRSAMD score was larger among Indians compared with that of the Chinese and had the thinnest thickness at the L9 central subfield (β = −1.00 μm; P = 2.91 × 10−7; R2 = 5.5%). Associations at other retinal layers and ETDRS regions were more heterogeneous. Conclusions: Overall genetic susceptibility to AMD and the aggregate effects of the complement cascade and lipoprotein metabolism pathway are associated most significantly with L7 and L9 photoreceptor thinning at the central macula in healthy individuals. Photoreceptor thinning has potential to be a prodromal AMD risk marker, and topographic variation should be considered. Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article

Tai Chi ( ) Pedicle Screw Placement for Severe Scoliosis

Objective: To evaluate the clinical safety and accuracy of the Tai Chi ( ) technique for placing pedicle screws, without intraoperative radiographic imaging, in severe scoliotic spines. Summary of Background Data: The current techniques for pedicle screw placement have a number of drawbacks in cases of severe scoliosis, including difficulty or impossibility to use, delayed operative time, requiring the presence of trained personnel for the duration of the surgery, high cost issues, increased radiation exposure, and technical challenges. No previous report has described the application of the Tai Chi pedicle screw placement technique for severe scoliosis. Material and Methods: Between 2006 and 2008, the cases of 39 consecutive patients with severe scoliosis (Cobb angle &gt;100 degrees) who underwent posterior correction and stabilization (from T1 to L5) using 992 transpedicular screws were examined. The mean patient age was 25.7 (range, 11 to 63) years at the time of surgery. Pedicle screws were inserted by the Tai Chi technique using anatomic landmarks and preoperative radiographs as a guide. Tai Chi drilling fully utilizes the natural anatomic and physical characteristics of pedicles and unconstrained circular force. By nature, a drill bit driven by unconstrained circular force would migrate within the pedicle along a path of least resistance, advancing along the central cancellous bone tunnel spontaneously. Accurate drilling was achieved by following the nature and sticking to the hand sensation when the drill bit broke through the cancellous bone. The total time for inserting all pedicle screws in each case was recorded. Postoperative computed tomography scans were performed to evaluate the position of the inserted pedicle screws. The screw position was classified as &quot;in&quot; or &quot;out.&quot; The distance of perforation was measured. Result: The average Cobb angle was 127 degrees (range, 100 to 153 degrees). The number of screws inserted at each level were as follows: T 1 (n = 10), T 2 (n = 34), T 3 (n = 46), T 4 (n = 53), T 5 (n = 61), T 6 (n = 69), T 7 (n = 75), T 8 (n = 76), T 9 (n = 76), T 10 (n = 77), T 11 (n = 76), T 12 (n = 78), L 1 (n = 77), L 2 (n = 68), L 3 (n = 56), L 4 (n = 38), and L 5 (n = 22). There were 923 (93%) &quot;in&quot; screws and 69 (7%) &quot;out&quot; screws. The overall accuracy of screw placement was 93%. There were no neurological, vascular, or visceral complications. No screws required postoperative repositioning. The average time for pedicle screw placement was 73 seconds. Conclusions: Our findings suggest that the Tai Chi pedicle screw placement technique, which does not require intraoperative radiographic imaging, is an accurate, reliable, safe, and timesaving method of placing pedicle screws in severe scoliotic spines

Six-Year Incidence of Visual Impairment in a Multiethnic Asian Population

Purpose: To examine the 6-year incidence of visual impairment (VI) and identify risk factors associated with VI in a multiethnic Asian population. Design: Prospective, population-based, cohort study. Participants: Adults aged ≥ 40 years were recruited from the Singapore Epidemiology of Eye Diseases cohort study at baseline. Eligible subjects were re-examined after 6 years. Subjects included in the final analysis had a mean age of 56.1 ± 8.9 years, and 2801 (50.5%) were female. Methods: All participants underwent standardized examination and interviewer-administered questionnaire at baseline. Incidences were standardized to the Singapore Population Census 2010. A Poisson binomial regression model was used to evaluate the associations between baseline factors and incident presenting VI. Main Outcome Measures: Incident presenting VI was assessed at the 6-year follow-up visit. Visual impairment (presenting visual acuity 60 years) contributed the highest population attributable risk to incident VI (27.1%), followed by lower monthly income (Singapore dollar < $2000; 26.4%) and smaller housing type (24.7%). Overall, undercorrected refractive error (49.1%) and cataract (82.6%) were leading causes for low vision and blindness, respectively. This was consistently observed across the 3 ethnicities. Conclusions: In this multiethnic Asian population, Malays had a higher VI incidence compared to Indians and Chinese. Leading causes of VI are mostly treatable, suggesting that more efforts are needed to further mitigate preventable visual loss. Financial Disclosure(s): The authors have no proprietary or commercial interest in any materials discussed in this article