What is Oculus Dexter?
OD or Oculus dexter is the Latin term that translates to “right eye”. An eyeglass prescription usually has three important medical abbreviations: OD (Oculus dexter), OS (Oculus Sinister), and OU (Oculus Uterque). The Latin term oculus translates to ‘eye’ in English, and dexter translates to ‘right’.
- OD or Oculus dexter is the Latin term that translates to “right eye”.
- If the OD numerical value has a minus sign (e.g. -2.00) then the person is nearsighted (myopic) in the right eye.
- If the OD numerical value has a plus sign (e.g. +2.00) the person is farsighted (hyperopic) in the right eye.
- If there are three numerical values (e.g. +2.00 -1.00 x180) the person also has astigmatism in the right eye.
Understanding Oculus Dexter
OD is the acronym for Oculus Dexter, which is used widely by ophthalmologists and optometrists. Most notably, OD is a term written in the glasses prescription indicating the prescription for the right eye.
The OD value, or right eye’s spectacle prescription, is the amount of lens power measured in Diopters (D), which is the correction for nearsightedness (myopia) or farsightedness (hyperopia). If the OD number is preceded by a negative sign (e.g. -1.00), the right eye is nearsighted. When the OD number is preceded by a positive sign (e.g. +1.00), the right eye is farsighted. If the value has neither a positive or negative sign, it is assumed that the value is positive (+) and the right eye is farsighted. If there are three numbers for OD (e.g. -1.00 +1.00 x045), then the right eye also has astigmatism.
Nearsightedness (-), also known as myopia, means that the eye can see clearly at near, such as reading, but has blurred vision for distance tasks such as driving. Conversely, farsightedness (+), also known as hyperopia, means that the eye sees clearly for distance tasks, but has blurred vision at near.
Astigmatism means that the cornea, the clear covering over the front of the eye, is not perfectly round, so the eye may have blurred vision both at near and distance.
Sphere (DS or SPH)
The glasses prescription may be a spherical measurement, often abbreviated as DS (Diopters Sphere) or SPH (Sphere). DS or SPH indicates that there is no astigmatism in the prescription, and hence the eye is “spherical,” or roundly shaped. If the cornea is spherical and round, then light bends the same way throughout the eye and the prescription is one single power. The DS or SPH is the lens power required to correct the vision. The sphere value may be (+) indicating farsightedness, or (-) indicating nearsightedness.
Understanding your spectacle prescription gives insight into the strength of your vision. A high amount of nearsightedness has risks that can affect the vision. High nearsightedness is defined as -6.00 D or greater. With high nearsightedness, the eye’s tissues become thin and stretched out and are more prone to tearing or breaking. Individuals with high nearsightedness should monitor for sudden visual changes that can indicate a retinal tear — such as flashes of light, a sudden increase in floaters, or a curtain covering the vision. An eye doctor should evaluate the eyes as soon as possible if these symptoms occur.
A high amount of farsightedness also has visual risks. High farsightedness is defined as +5.00 or greater. Children with high farsightedness are more likely to have strabismus, also known as a lazy eye. High farsightedness may impede children from doing near tasks such as reading and homework and can affect school performance. Furthermore, high farsightedness may cause eye strain or headaches.
Cylindrical (DC or CYL)
If the glasses prescription has a numerical value under the ‘CYL’ column, it indicates that the eye has astigmatism. This may be written as DC (Diopters Cylinder) or CYL (Cylinder). The cylinder value describes the amount of astigmatism. Optometrists commonly write prescriptions in minus cylinder (e.g. -2.00 x180) while ophthalmologists tend to use plus cylinder (e.g. +2.00 x090). Astigmatism means that the cornea, the clear covering over the front of the eye, is not perfectly round, and instead is more oval-shaped. This causes light entering the eye to bend differently and not focus to a single point in the retina. Astigmatism can be corrected with a glasses prescription, similar to nearsightedness or farsightedness.
Having a high amount of astigmatism also can pose a threat to the vision. High astigmatism is defined as 3.00 DC or greater. In rare cases, a high amount of astigmatism may be associated with keratoconus, a corneal disease that causes progressive thinning and bulging of the cornea.
The axis indicates the direction of astigmatism. Axis is the direction, in degrees, that light needs to enter the eye in order to be properly focused for an irregularly shaped cornea. The axis follows the “x” on the prescription. The axis of astigmatism depends on if the eye doctor uses a minus (-) or plus (+) cylinder to write your prescription. The axis is 90 degrees apart for minus cylinder and plus cylinder. For example, if the doctor writes a prescription for “0.00 +1.00 x090”, this is the same prescription as “+1.00 -1.00 x180”. Astigmatism axis ranges from 001 to 180 degrees.
The ADD power value of the glasses prescription is the amount of additional power that is added to the distance prescription. The ADD power is only indicated for glasses with multiple prescription powers such as progressive lenses, bifocals, or powerboost lenses. ADD powers are typically used for patients who have trouble focusing at near tasks, such as patients 40 years or older, or young patients with weak focusing systems or abnormal eye postures. The ADD power is added to the distance prescription to make the near vision clear for up-close activities such as reading, writing, or needling.
Single Vision Or Multifocal
When purchasing glasses, it is important to note whether you need a single vision or multifocal prescription. Single vision prescriptions have the same power throughout the entire lens. Single vision prescriptions are typically prescribed for young people who do not need additional reading power. Single vision prescriptions do not have an ADD power.
Multifocal lenses have multiple prescriptions combined into one lens. In most cases, the top part of the lens has the distance prescription and the bottom part of the lens has the reading prescription. Examples of multifocal lenses are progressive lenses, bifocals, and powerboost lenses. Multifocal lenses have an ADD power that indicates how much extra power is added for reading.
In rare cases, the glasses prescription indicates the amount of prism. Most patients do not have prisms in their glasses and this amount is left blank on the prescription. Prism may be prescribed for people who have lazy eye, double vision, or trouble with eye muscle coordination. Prism incorporated into glasses changes the direction of light entering the eyes, so that the image viewed through the glasses is moved in space. If prism is present, the prescription will also indicate the amount and direction of prism. The prism direction may be BI (base in), BO (base out), BU (base up), or BD (base down). For example, the prism value may be written as “2.00 BI”.