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Calculation of CSR and CSC and visual acuity thresholds

Calculation of CSR and CSC and visual acuity thresholds. IAPB 9GA Hyderabad 2012. G V S Murthy. Improving health worldwide. Improving health worldwide. www.iceh.org.uk www.lshtm.ac.uk. www.iceh.org.uk www.lshtm.ac.uk. Institutional Affiliation. Reader,

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Calculation of CSR and CSC and visual acuity thresholds

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  1. Calculation of CSR and CSC and visual acuity thresholds IAPB 9GA Hyderabad 2012 G V S Murthy Improving health worldwide Improving health worldwide www.iceh.org.uk www.lshtm.ac.uk www.iceh.org.uk www.lshtm.ac.uk

  2. Institutional Affiliation Reader, International Centre for Eye Health, Department of Clinical Research, Faculty of Infectious and Tropical Diseases , London School of Hygiene and Tropical Medicine & Director, Indian Institute of Public Health, Public Health Foundation of India, Hyderabad Improving health worldwide www.iceh.org.uk www.lshtm.ac.uk

  3. Acknowledgements • Dr Hans Limburg • Dr B R Shamanna Their inputs were critical to this presentation

  4. Characteristics • Cataract Surgical Rate (CSR) uses the population as the denominator • Cataract Surgical Coverage (CSC) uses operated persons in the community as the denominator. • Both can be used in conjunction to compare performance and pending workload at regional/ national level.

  5. Cataract Surgical Rate (CSR) Number of cataract operations (eyes) conducted per million population per year • Indicator for output on cataract intervention • Denominator is total population while cataract occurs mainly in people 50+ • Who is operated? (age, sex, 1st or 2nd eye, VA?) • Depends on accuracy of data collection • Risk of over- or under-reporting

  6. What data is needed to calculate CSR? • Population of administrative area • Quantum of cataract surgeries (operated eyes) • Time period when above events occur – i.e. specific year • Usually obtained from secondary data sources.

  7. Cataract Surgical Rate No. of Cataract Surgeries/ Year x 106 Population in Defined Area Cataract Surgeries refers to Operated Eyes

  8. Cataract Surgical Coverage (CSC) Objective: • coverage indicator • measures accessibility & utilization of services • measures actual community level situation • independent of reporting system Assumption: • VA at time of surgery not known: use VA threshold conforming to surgical practice in survey area

  9. Cataract Surgical coverage Sources of Data: • Surveys • RACSS/RAAB

  10. What data is needed to calculate CSC? • No. of cataract blind/visually impaired • Quantum of cataract surgeries (eyes/persons) • Time period when above events occur – i.e. specific year • Valid data generally possible only from primary sources in LMIC . i.e. RAAB

  11. Defining CSC • Can be calculated at person level or operated eye level • Can be calculated at different visual acuity levels (based on a country’s needs/ surgical practices) • VA<3/60: cataract blind eye or person • VA<6/60: severely visually impaired cataract eye or person • VA<6/18: visually impaired cataract eye or person

  12. Calculating CSC CSC eyes:(a/a+b) x 100 Where: a = no. (pseudo)aphakic eyes b = no. eyes with operable cataract (BCVA<3/60; <6/60; <6/18) CSC persons: (x + y/x + y + z) x 100 Where: x = persons with bilateral (pseudo)aphakia y = persons with 1 (pseudo)aphakic and 1 operable cataract z = persons with bilateral operable cataract (BCVA<3/60; <6/60; <6/18)

  13. THANK YOU

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