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Pinhole test
The pinhole test is used to determine whether the patient’s reduced visual acuity is a refractive error or pathological. In refractive errors, the pinhole test will produce a better result than the unaided visual acuity. The pinhole blocks out peripheral rays, to allow for a clearer image on the retina. No improvement in visual acuity with a pinhole, usually means the reduced vision is based on ocular pathology or neurological disease.

Duochrome
The duochrome test is used to determine whether a patient has been overcorrected. It is based on the principles of chromatic aberration – the shorter the wavelength of the light, the more it is deviated on refraction. The duochrome test comprises of two ranks of black letters on red (longer wavelength) and green (shorter wavelength) backgrounds. An uncorrected myope usually will see the letters on the red background clearer, as red focuses closer to the retina than the green, due to their longer axial length. The patient is asked, “On what colour, red or green, do the black letters stand out more?” Patient’s responses: Emmetrope: red = green Under-corrected myope: red slightly Over-corrected myope: red Corrected hypermetrope: Red= green Under-corrected hypermetrope: green Over-corrected hypermetrope: red

Near Add
A supplementary convex lens may be used in a presbyopic patient. Presbyopia is defined when a person has reduced amplitude of accommodation, and therefore has difficulty with near vision. The amplitude of accommodation declines with age, and usually begins after 40 years of age. The near add correction depends on the distance the patient likes to read. You can estimate a patient’s near add based on their age: