Objective testing of near vision

October 1, 2010

Although near vision can never be assessed objectively, standardization between tests would be useful. However, there is a lack of standardization between tests so that comparison of results of different near vision tests is difficult, or not possible. Dr Oliver Findl explains.

High incidence of presbyopia in patients over the age of 45 years and a growing demand for spectacle independence has led to an increasing interest in presbyopia treatments, such as multifocal intraocular lenses (IOLs),1 so-called accommodating IOLs,2 different kinds of corneal treatments and lens refilling,3 as alternatives to wearing reading glasses. Results of these treatments are usually evaluated using near or reading vision as main outcome parameters. Although near vision can never be assessed objectively, standardization between tests would be useful. However, as shown below, there is a lack of standardization between tests so that comparison of results of different near vision tests is difficult, or not possible.

In contrast to functional vision, where reading conditions can be varied and a situation close to real life is simulated, reading tests usually assess only single parameters of functional vision, such as near acuity or reading speed. Furthermore, it must be clarified as to whether mainly optical factors should be evaluated, then letter tests are usually appropriate, but if reading acuity should be assessed, reading tests are necessary.4

A large variety of these near charts is available, such as the Fonda-Anderson reading card that represents every day life situations (such as telephone book print), but the disadvantage here is that this reading card does not cover the upper range of reading acuity, or the Bailey and Lovie reading charts that use a Times Roman style font, a common font in every day life situations. It was shown that different font designs have an impact on near acuity, so, for example, the font design Courier has a small, but clinically significant advantage over Times New Roman, when patients with low vision were tested. Furthermore, Jaeger Reading charts are available that are used mainly in German speaking countries, or reading charts by Colenbrander that are also available as 'mixed contrast reading cards' to allow assessment of reading acuity under low contrast conditions. Further developments, such as the MNRead Acuity charts5 were developed as continuous-text reading acuity charts that can be used in subjects with normal and low vision. These charts allow a doctor to assess reading acuity, reading speed and critical print size. Radner Reading charts follow a similar principle as the MNRead Acuity charts and were also shown to be highly reliable.6 In contrast to these reading charts the Practical Near Acuity Chart (PNAC) uses only three words per line and the print size decreases with each line.