At the end of an eye examination, during which visual acuity was assessed, a sheet is given in which the parameters for contact lenses (LAC) are indicated. This prescription contains technical acronyms that describe the needs for corrective lenses. A prescription for contact lenses describes the type of ACL you need to compensate for the refractive defect in your eyes and thus allow you to see normally. Once you understand the terms and abbreviations, you will be able to read the prescription for LACs without any problem.
Steps
Part 1 of 2: Read the Typical Lens Prescription
Step 1. Find your prescription
When the ophthalmologist gives you the examination report, he also gives you the prescription for the lenses. It typically looks like a chart or table and is part of the clinical record. Although this is its standard format, the terms on the various columns or axes vary according to the physician's preferences.
Be sure to read the prescription for LACs and not the prescription for eyeglass lenses. This way you are sure you understand exactly what type of lenses you need to buy. The graph for contact lenses and the graph for glasses may have similar acronyms, but the numbers may be different
Step 2. Find the general information
A prescription must contain the essential data of the doctor who issued it and those of the patient. This means that you must be able to read the patient's name and surname, the date on which the visit was carried out, the one on which the prescription was issued, the period of validity of the same and the name, surname, address, telephone number and fax of the doctor.
Information regarding the power of the lenses should be noted along with all other specific indications, brand recommendations and instructions
Step 3. Understand the main terms
Each LAC prescription lists the power of correction for each eye. On the sheet you can then read the words "right eye" and "left eye" or the abbreviations "OD" and "OS". If your eyes need lenses of equal power, then you can read "both eyes" or "OO".
Most of the values present on a prescription for contact lenses are expressed in diopters, the unit of measurement of refractive power, which is equal to the reciprocal of the focal distance expressed in meters of the lens itself. Diopters are often abbreviated with the letter "D"
Step 4. Locate the power (PWR) or sphere (SF) values
These numbers are usually the first you can see next to the abbreviations "OD" and "OS" in their respective rows or columns. These values indicate the "strength" of the corrective lens for each eye or for both, if the wording "OO" is reported. If the numbers are positive, then you are farsighted; if they are negative, then you are nearsighted.
- For example, if in the space below "OD" you see the number -3.50 D, then it means your right eye is 3.50 diopters short-sighted. If, on the other hand, you find the value +2, 00 D, the right eye is farsighted by two diopters.
- It is not uncommon for the optical correction to be different for the two eyes. If you find the abbreviation "PL", which means "plano", then you have to assume that the number is 0 and that eye does not need correction.
Step 5. Understand the base radius (BC)
This value describes the internal curvature of the LAC. This is an important parameter so that the lens fits perfectly on the eye and adapts to the shape of the cornea. Unlike the other values, the base radius is expressed in millimeters (mm).
This number is usually between 8 and 10. The lower the number, the more curved the cornea
Step 6. Find the diameter (DIA)
This parameter indicates the length of the straight segment that passes through the center of the contact lens. Basically it tells you how big the lens has to be to fit the eye. Just like the base radius, the diameter is also expressed in millimeters.
This is a very important value. If incorrect, ACL would cause irritation or even corneal abrasions
Step 7. Buy the right brand
In Italy, an ophthalmologist rarely prescribes a specific brand of contact lenses; however, he can give you advice on the type or material. If your doctor also notes any suggestions on this, the optician to whom you deliver the prescription will have to respect them.
The optician will be able to recommend similar brands or generic products that comply with medical indications. Contact lenses can only be sold by licensed professionals
Step 8. Understand the lens equation
In some cases the prescription looks like an equation following this order: +/- Sphere / Power +/- Cylinder x Axis, Base Radius BC = Diameter DIA = number. For example: +2, 25-1, 50x110, BC = 8, 8 DIA = 14, 0.
If you are unsure about the equation, ask your doctor to explain it to you
Part 2 of 2: Read a More Complex Prescription for Lenses
Step 1. Look for the cylinder value (CYL)
Some numbers are not always present in a prescription. People who have astigmatism, a widespread refractive error, may notice an extra row or column in which the abbreviation "CYL" appears. This number measures the amount of the patient's astigmatism expressed in diopters. Most eye doctors express this value with a positive number, but if your doctor writes it as a negative number, the optician will be able to convert.
- The presence of the value of astigmatism assumes that the patient has a cornea or lens with an irregular shape.
- If the value is negative we speak of myopic astigmatism, otherwise the astigmatism is of the hypermetropic type.
Step 2. Find the axis value (AX)
This number is expressed in degrees and is essential to deflect light correctly and compensate for corneal irregularity. In practice, it is the inclination to which the power of the cylinder must be placed in order for astigmatism to be corrected.
The value can be quite high, such as 90 or 160, depending on the angle that the cylinder must respect
Step 3. Understand the value of addition (ADD)
This parameter is indicated when the patient needs bifocal contact lenses. In this case the prescription has a column or row for the "ADD" value which is the additional power needed to be able to read closely and therefore to purchase the right LACs.
This value is also expressed in diopters
Step 4. Ask your optician for more details about color (sometimes you can read "color" on LAC packages)
This additional parameter is indicated for some types of contact lenses that enhance the natural color of the eyes. It is also indicated for some special LACs such as "cat's eye" or with other particular characteristics.
