Stratification of Normative Data Linda M. Zangwill, Ph.D. Professor Hamilton Glaucoma Center Diagnostic Imaging Laboratories Department of Ophthalmology University of California, San Diego

Financial Disclosures National Eye Institute Research Support: EYR0111008, EYU1014267, EYR01019869 Research Instrument Support: Heidelberg Engineering Carl Zeiss Meditec Optovue Nidek Topcon Reading Center Services:

Questions To Be Covered: Stratification in Normative Databases What magnitude of difference between subgroups is clinically important to warrant stratified databases or adjustment of the normal limits? For which covariates are covariate specific normal limits needed? How should individuals be selected with respect to the covariates to construct the database?  

Candidate Covariates for Stratification/ Adjustment (Consistent Evidence: histology, clinical imaging studies) Age Race Optic disc size Image quality (signal strength) Axial length/Refractive error

Ganglion Cell Adjustment Signal strength, Disc area SDOCT Normative Database Covariate Adjustments (Retinal Nerve Fiber Layer (RNFL) and Optic Nerve Head (ONH)) Device Number Subjects Age Mean (range) Race RNFL Adjustment ONH Adjustment Ganglion Cell Adjustment RTVue 480 49.4 (18-84) 33% Caucasian 22% Asian 20% African 12% Hispanic 12% Indian Age, Signal strength, Disc area Signal strength Cirrus 284 (19-84) 43% Caucasian 24% Asian 18% African 1% Indian Disc area Spectralis 201 48 ± 14 (18-78) Caucasian Only (Not all Sectors)

Ganglion Cell Adjustment Signal strength, Disc area SDOCT Normative Database Covariate Adjustments (Retinal Nerve Fiber Layer (RNFL) and Optic Nerve Head (ONH)) Device Number Subjects Age Mean (range) Race RNFL Adjustment ONH Adjustment Ganglion Cell Adjustment RTVue 480 49.4 (18-84) 33% Caucasian 22% Asian 20% African 12% Hispanic 12% Indian Age, Signal strength, Disc area Signal strength Cirrus 284 (19-84) 43% Caucasian 24% Asian 18% African 1% Indian Disc area Spectralis 201 48 ± 14 (18-78) Caucasian Only (Not all Sectors)

Age: What is the Evidence?

RNFL Age Related Decrease RTVue Rate of decrease: -.17 um / yr R2=7.0% Cirrus Rate of decrease: -.19 um / yr R2=11.8% RTVue Sinai copyright 2010 PN 300-46043 Rev A Girkin et al. Ophthalmol 2011 Mwanza et al AJO 2011

RNFL Age Related Decrease: Magnitude < 10 um between 40-80 years RTVue Rate of decrease: -.17 um / yr R2=7.0% Cirrus Rate of decrease: -.19 um / yr R2=11.8% RTVue Sinai copyright 2010 PN 300-46043 Rev A Girkin et al. Ophthalmol 2011 Mwanza et al AJO 2011

Rate varies by sector and baseline thickness 0 Rate varies by sector and baseline thickness 0.21 um/yr (temporal) to -1.35 um/yr (Superior) Cirrus RNFL Sector Longitudinal* (n=35) um/yr (95% CI) Average -0.52 (- 0.86 to -0.17) Superior -1.35 (- 2.05 to -0.65) Inferior -1.25 (- 1.78 to -0.71) Temporal 0.21 (- 0.10 tp0.53) Nasal 0.31 (- 0.25 to 0.86) * Adjusted for disc area, signal strength, refraction Mean follow-up 30 months Range 24-41 months Leung et al 2012 Ophthalmol 119:731-737

Adjust for Age? For Against Small, significant differences SDOCT Histology and other imaging Age explains variability RNFL: R2 = 7% -12% Rim Area: R2 = 3-5% Rate of RNFL decrease Global: 0.17 to 0.52 um/yr Sectors: Faster rate of change May help differentiate between age-related and OAG damage Against Small, significant differences Between 40 and 80 yrs difference in RNFL is small : < 10 um Large variation Varies by sector Varies by baseline thickness

Race: What is the Evidence?

Racial Differences in Disc Area (African, Hispanic > European) AD: African ED: European HE: Hispanic IN: Indian JA: Japanese Girkin et al. Ophthalmol 2011

Small significant differences by race for some parameters even after adjusting for disc area and age Cirrus RTVue Girkin et al. Ophthalmol 2011 Knight et al. Arch Ophthalmol 2012

Small significant differences by race for some parameters even after adjusting for disc area and age Cirrus RTVue Largest difference in mean Rim area between races =0.21 mm2 (Hispanic: 1.48 mm2 vs Indian:1.27 mm2) Largest difference in mean Rim area between races =0.09 mm2 (Hispanic: 1.38 mm2 vs European:1.29 mm2) Girkin et al. Ophthalmol 2011 Knight et al. Arch Ophthalmol 2012

Rim Area Average RNFL Normal Comparison Group: AD and ED from the RTVue Normative Database (n=167)

RNFL Diagnostic Accuracy is Similar Regardless of Whether Normal Comparison Group is of European or African Descent Girkin et al IOVS 2011: 52: 6148-53

Stratify by Race? For Against Clear evidence of optic nerve head racial differences (not “small”) Misclassification of Individuals will be reduced Against How to define group? self report Large variation within groups Hispanic (Mexican? South American?) African (West Africa? Caribbean?) Asian (Japanese? Chinese? Indian?) Evidence that overall diagnostic accuracy is similar Other parameters (i.e. disc area) explain most of the racial variation Added expense/sample size/sites for stratified race-specific databases

Optic Disc Size: What is the Evidence?

Strong Associations of ONH Parameters w/Disc Area R2 ranged from 5 Strong Associations of ONH Parameters w/Disc Area R2 ranged from 5.2% (RNFL) to 42.6% (Cup Area) (RTVue) Sinai white Paper PN 300-46043 Rev A

Strength of Disc Area Association with Vertical Cup Disc Ratio Varies by Instrument RTVue R2=19.3% Cirrus R2=52.7% Sinai white Paper PN 300-46043 Rev A Knight et al Arch Ophthalmol 2012

Adjust for Optic Disc Size? Explains a large proportion of the variability in optic nerve head parameters (large R2) Explains much of the variation by race without the need for separate databases Is readily available -measured by SDOCT instruments Against Automated software delineation of disc margin is not always accurate

Signal Strength and Axial Length Statistically Significant but small R2 R2 =3.7% (RTVue) Axial Length R2 < 7% RNFL and ONH (Cirrus*) Sinai White Paper PN 300-46043 Rev A *Cirrus User Manual 2660021142073 D

Adjust for Signal Strength and Axial Length? Consistent evidence of weak associations with RNFL and ONH parameters Against Explains a small proportion of the variability in RNFL and ONH parameters (small R2)

Summary Importance of Covariate Depends On: What is measured: RNFL vs. Optic nerve head (ONH) Magnitude of difference and/or strength of the association -Can be statistically significant, but weakly associated (small difference or R2) Whether another covariate explains the heterogeneity (disc area and race) Instrument – segmentation and other differences Sector Is consistency of adjustment important?

Stratification in Normative Databases What magnitude of difference between subgroups is clinically important to warrant stratified databases or adjustment of the normal limits? Difficult to set a specific magnitude – perhaps a minimum R2 and/or clinically important difference should be required Clinically important is different from statistically significant For which covariates are covariate specific limits needed? Strongest evidence for age for RNFL and disc size for ONH How should individuals be selected with respect to the covariates to construct the database? Large range, yet relevant to the disease i.e. Older ages well represented

Thank You