Prevalence of Visual Impairment in Portugal: study design and initial results

Abstract

 

Purpose

 

Information about the prevalence of visual impairment is fundamental to define policies that deal with vision loss. The aim of this study is to determine the prevalence of visual impairment (VI) in the population looking for eye care in public hospitals in Portugal.

 

Methods

 

We designed an observation, cross-sectional prospective study (Prevalence and Costs of Visual Impairment in Portugal: PC-VIP study) to investigate the prevalence of VI in patients attending outpatient appointments in four public hospitals in Portugal. Hospital selected provide from general eye care (3-6 ophthalmologists) to high-specialized eye care (40+ ophthalmologists) that in total have between 120-140K hospital appointments per year. Files of patients are analysed weekly to detect patients with VI. Inclusion criteria were: visual acuity equal or worse than 0.5 (USA definition 20/40) in the better eye and/or a visual field of less than 20deg. Cases are selected by trained hospital staff and inserted in a database. Data collected included demographic information, acuity from both eyes, qualitative information about visual field (good, reduced, requires investigation), main diagnosis, secondary diagnosis and comorbidities. Diagnoses were classified according with ICD9.

 

Results

 

We have now detected 2462 cases of VI that correspond to 4 to 33 weeks of data collection. The number of weeks is variable because collection did not start simultaneously in all sites. From the number of cases detected, 58% were female, 1.9% were under 20y, 8.2% were between 20y and 50y and 89.9% were ≥50y. The mean prevalence of visual impairment was 13.6% (SD=5.6) using the USA definition and it was 7.0%(SD=4.1) using the WHO definition (acuity equal or worse than 0.3 or ~20/63). With a methodology that controls for demographics the lowest and highest estimates were calculated. Considering the USA definition, the prevalence in the general population would be in the range 0.4 -0.4% (age<40y) and 0.8-2.4% (age>=40y). Considering WHO definition, it would be 0.2-0.5% (age<40y) and 0.4-1.0% (age>=40y).

 

Conclusions

 

A hospital-based study can provide effective estimates of the prevalence of visual impairment in a population. Estimates for the country are in agreement with the expected results that can be deducted from neighbour countries and self-reported visual impairment in census 2001.