How To Read Eyeglass Or Contact Lens Prescription

This prescription shows that the patient has 2.75 diopters of myopia with 1.25 diopters of astigmatism at an angle of 15 degrees in the right eye, and the left eye is plano with 0.75 diopters of astigmatism at an angle of 85 degrees.

Minus Cylinder or Plus Cylinder

Spectacle prescriptions can be written in two value sets, minus cylinder or plus cylinder, which are mutually exclusive of each other but provide the same information. As a rule, ophthalmologists write scripts in minus cylinder whereas optometrists write scripts in plus cylinder. Why these two professions cannot get together and decide on a common method of reporting refractive error is impossible to explain, but if you have ever had competing siblings in your family, you may get an idea why this has not yet occurred.

To convert a minus cylinder form prescription into plus cylinder, or to convert the plus cylinder form into minus cylinder, do the following:

1) Add the sphere and cylinder powers together; this becomes the new sphere power.
2) Change the sign of the cylinder power, from minus (–) to plus (+) or from plus (+) to minus (–).
3) Change the axis value by 90?, remembering that the axis must be a number from 1 to 180.
The following lens prescriptions, therefore, are equivalent and interchangeable:

Spherical Equivalent

The spherical equivalent power of a lens prescription is the average of the dioptric powers in all meridians of a lens. To obtain this value, add half of the cylinder power to the sphere power. In other words, do the following:

1) Divide the cylinder power by 2.
2) Add this value to the sphere power; the result is the equivalent sphere power of the lens.

For the glasses prescription...

...the equivalent sphere powers of each lens would be calculated as follows:

OD: –2.75 D + (–1.25 D ÷2) = 2.75 D + 0.625 D = –3.375 D
OS: 0.00 D + (–0.75 D ÷2) = 0.00 D + 0.375 D = –0.375 D

---

Current Spectacle and Contact Lens Medical Journal News...

Evaluation of Image Quality Metrics for the Prediction of Subjective Best Focus.

Related Articles

Evaluation of Image Quality Metrics for the Prediction of Subjective Best Focus.

Optom Vis Sci. 2010 Jan 30;

Authors: Kilintari M, Pallikaris A, Tsiklis N, Ginis HS

PURPOSE.: Seven existing and three new image quality metrics were evaluated in terms of their effectiveness in predicting subjective cycloplegic refraction. METHODS.: Monochromatic wavefront aberrations (WA) were measured in 70 eyes using a Shack-Hartmann based device (Complete Ophthalmic Analysis System; Wavefront Sciences). Subjective cycloplegic spherocylindrical correction was obtained using a standard manifest refraction procedure. The dioptric amount required to optimize each metric was calculated and compared with the subjective refraction result. Metrics included monochromatic and polychromatic variants, as well as variants taking into consideration the Stiles and Crawford effect (SCE). WA measurements were performed using infrared light and converted to visible before all calculations. RESULTS.: The mean difference between subjective cycloplegic and WA-derived spherical refraction ranged from 0.17 to 0.36 diopters (D), while paraxial curvature resulted in a difference of 0.68 D. Monochromatic metrics exhibited smaller mean differences between subjective cycloplegic and objective refraction. Consideration of the SCE reduced the standard deviation (SD) of the difference between subjective and objective refraction. CONCLUSIONS.: All metrics exhibited similar performance in terms of accuracy and precision. We hypothesize that errors pertaining to the conversion between infrared and visible wavelengths rather than calculation method may be the limiting factor in determining objective best focus from near infrared WA measurements.

PMID: 20125061 [PubMed - as supplied by publisher]