title: Factors affecting signal strength in spectral-domain optical coherence tomography.
abstract: OBJECTIVE
  To identify ocular factors that affect signal strength in spectral-domain optical coherence tomography (SD-OCT).
  
  
  METHODS
  Data from 1312 participants of the population-based Singapore Malay Eye Study-2 (SiMES-2) were included in the analysis. All participants underwent standardized ophthalmic examination, including measurements of best-corrected visual acuity (BCVA), refractive error, axial length, corneal curvature and presence of cataracts. Optic disc and macular cube scans were acquired using the Cirrus HD-OCT (software version 6.0, Carl Zeiss Meditec, Dublin, CA, USA). Signal strength of the optical coherence tomography (OCT) scan was recorded for each study eye. Multivariable linear regression analyses were performed to evaluate the associations between ocular factors and signal strength of the OCT scans.
  
  
  RESULTS
  The mean (±SD) age of our study participants was 61 ± 9 years, and 44.6% were male. Mean optic disc scan signal strength was 7.90 ± 1.25, range = 0-10, while mean macular scan signal strength was 8.80 ± 1.27, range = 0-10. In multivariable regression analyses, poorer signal strength in optic disc and macular cube scans was each associated with older age (per decade, β = -0.373, p < 0.001; β = -0.373, p < 0.001, respectively), poorer BCVA (per logMAR line; β = -0.123, p < 0.001; β = -0.156, p < 0.001, respectively), greater degree of myopia (per negative dioptre of spherical equivalent; β = -0.112, p < 0.001; β = -0.117, p < 0.001, respectively), presence of cortical cataracts (β = -0.331, p < 0.001; β = -0.314, p < 0.001, respectively) and presence of posterior subcapsular cataracts (β = -0.910, p < 0.001; β = -0.797, p < 0.001, respectively).
  
  
  CONCLUSIONS
  We found that older age, poorer BCVA, greater degree of myopia and presence of cortical and posterior subcapsular cataracts were associated with reduced signal strength in Cirrus SD-OCT. Our findings provide information on the barriers to obtaining good image quality when using SD-OCT, and allow clinicians to potentially identify individuals who are more likely to have unreliable OCT measurements.
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore.|Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
authors.forename: Ryan
authors.initials: R
authors.lastname: Lee
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore.|Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
authors.forename: Yih-Chung
authors.initials: YC
authors.lastname: Tham
authors.affiliation: Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Carol Y
authors.initials: CY
authors.lastname: Cheung
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Sidhartha
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore.|National Healthcare Group Eye Institute, Tan Tock Seng Hospital, Singapore, Singapore.
authors.forename: Rosalynn Grace
authors.initials: RG
authors.lastname: Siantar
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore.
authors.forename: Sing-Hui
authors.initials: SH
authors.lastname: Lim
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore.|Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.|Duke-NUS Medical School, Singapore, Singapore.
authors.forename: Tien Yin
authors.initials: TY
authors.lastname: Wong
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore.|Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.|Duke-NUS Medical School, Singapore, Singapore.
authors.forename: Ching-Yu
authors.identifier: http://orcid.org/0000-0003-0655-885X
authors.initials: CY
authors.lastname: Cheng
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002386:Cataract / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008266:Macula Lutea / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000175:diagnosis*; D009898:Optic Disk / Q000000981:diagnostic imaging*; D015203:Reproducibility of Results; D041623:Tomography, Optical Coherence / Q000379:methods*
keywords: image quality; ocular imaging; optical coherence tomography; signal strength