Traditionally refraction still serves as the basis for spectacle prescriptions. This is the result of a two-part process:

• Objective refraction: The refractive errors of the eye are first estimated objectively using retinoscopy or an automated refractor followed by
• Subjective refraction: A prescription is subjectively refined by an optometrist, allowing the patient to compare their vision through trial lenses, using either a refractor head or trial frame.

Subjective refraction uses different spectacle lens powers to correct refractive errors (such as myopia, hyperopia or astigmatism) in the eye, which are called low order aberrations, LOAs.

However, due to variations in pupil size with varying light conditions, other types of aberrations appear, affecting the quality of vision. These affect the final quality of vision experienced by the wearer. This is referred to as high order aberrations, HOAs (e.g. coma, trefoil, and spherical aberration).

i.Scription^® Technology by ZEISS is based on the ZEISS eye measuring system called the i.Profiler^{® plus}, specifically designed to determine the exact “fingerprint” of the eyes and provide measurements unique to the patient’s eyes.

ZEISS i.Scription prescription takes into account the effects of low and high order aberrations on retinal image quality by measuring up to 1500 points on each eye. This is done to provide improved vision corrections that deliver optimal visual performance over a broader range of luminance levels, even under demanding viewing conditions like night driving.

i.Scription^® Technology analyses the circle of least confusion to provide the most accurate prescription possible

Conventional manifest refraction is performed in well illuminated rooms, leading to prescription values that work well in daylight situations. However, as the pupil dilates in low light conditions, the peripheral aberrations of the eye can lead to refractive shifts, resulting in a conventional prescription which is no longer valid.

• Subjects rated ZEISS lenses with i.Scription higher for distance vision, night vision, and colour perception.³
• ZEISS lenses with i.Scription Technology also performed better on average than conventional spectacle lenses in measures of mesopic visual acuity and contrast sensitivity.³
• Subjects with low- to moderate-prescription powers preferred ZEISS lenses with i.Scription Technology more often for distance vision, active vision, sharpness, changing focus, and overall vision.⁴
• Subjects preferred ZEISS lenses with i.Scription Technology more often for night vision, vividness of colours, and having less glare.⁴
• ZEISS lenses with i.Scription Technology also performed better than conventional spectacle lenses in measures of low-contrast, mesopic visual acuity by approximately half a line of acuity.⁴