Introduction Of Some Terms Regarding Colored Contacts

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What Does DIA (Diameter) Mean in Contact Lenses?

The full name of DIA is Diameter, meaning 14.00mm,14.20mm,14.50mm,22mm in diameter.

soft colored contact lenses

According to the diameter size can be divided into three kinds:

  • Small diameter: 13.8mm-14.0mm (suitable for small eyes)
  • Medium diameter: 14.0mm-14.2mm (suitable for most people natural and dilated pupil effect)
  • Large diameter: 14.2mm-14.5mm (this is suitable for large eyes)


According to the size of the coloring diameter, it can be divided into three types:

  • Small diameter: coloring diameter ≤ 13.2mm
  • Medium diameter: coloring diameter in 13.4mm-13.6mm
  • Large diameter: coloring diameter: coloring diameter ≥ 13.8mm


The larger the tinting diameter, the more exaggerated the effect. And, the larger the total diameter of the lens, the less the area of the eye in contact with oxygen and the less the comfort. When choosing a diameter, you can refer to the golden ratio of pupil size popular in the fashion world - sclera:pupil:sclera = 1:2:1, when the eyes are naturally enlarged.

What Does BC (Base Curve) Mean in Contact Lenses?

Base Curve's full name is Base Curve. BC refers to the base curve of a contact, and the base curve is the curvature of the contact, which is commonly used at around 8.6mm, with 0.1mm up and down fluctuations on top of the 8.6mm used. The routine base curve is 0.2mm higher than a person's normal corneal base curve, so there is no significant pressure on the cornea or the possibility of contact with the cornea, making it more appropriate to wear.

The base curve (BC) refers to the radius of curvature of the lens, and the larger the base curve, the flatter the inner surface of the lens. The size of the base curve is related to the comfort of wearing contacts.

If the base curve > the base curve of the eye, the eye and the lens may not fit together, which is often referred to as the slippage phenomenon.

If the base curve of the lens is less than the base curve of the eye, the eye may feel too tight and uncomfortable, and the eye may feel constricted, even affecting eye health.

The majority of people have an eye arc between 84-86, and the difference between the base curve and eye arc of contacts should be controlled to within 0.2mm. First-time wearers can consult the exact value at an optician or eye hospital, and if you don't know your exact base curve, you can start with 86mm to make it easier to make mistakes.

What Does CT (Center Thincknes) Mean in Contact Lenses?

The thickness of the lens influences its elasticity, formability, durability, and wearing comfort.

Patients with astigmatism prefer thicker lenses because they have a higher modulus of elasticity, are more formable, and the gap between the lens and the cornea is partially filled with tears, reducing the effect of astigmatism. Thin lenses can change shape due to corneal morphology and do not provide an optimal optical interface.

Thin and poorly formed lenses are not appropriate for first-time wearers because they are difficult to operate.

Thin lenses should be used for higher diopters to increase oxygen permeability and comfort.

Thicker lenses should be chosen by patients with drier eyes to reduce tear evaporation.

What Influences OP (Oxygen Permeability) in Contact Lenses?

  • Lens tightness - a slightly loose lens can allow free circulation of tears.
  • Lens design - make the curvature of the inner surface of the lens match the curvature of the cornea as much as possible, so that the lens floats on the tear fluid to increase the purpose of oxygen permeation.
  • Altitude and temperature - the oxygen in the air is reduced, the cornea is hypoxic, the higher the temperature, the thinner the oxygen in the air.
  • The choice of lenses - silicone hydrogel oxygen permeability is higher than hydrogel.
  • Lens thickness - the thinner the lens, the higher the oxygen permeability.
  • Tear film quality - dry eyes affect oxygen permeability (through hot compresses or eye lubricant, artificial tears to relieve symptoms).

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