? The scientific name of contact lenses: corneal contact lenses.
? English name: contact lens, abbreviation: CL
? Currently, soft hydrophilic contact lenses are mainly sold on the market. (Generally, without special explanation, what people call "contact lenses" refers to soft contact lenses.)
History of CL
? 1508, Leonardo da Vinci, the first to draw CL sketch, explaining the origin of relevant theories
? In 1948, American optometrist Kevin Toch pioneered the first corneal PMMA material lens CL. CL was born
? 1963, Czech Otto Wei Teller obtained the HEMA material patent and is known as the "Father of Modern Contact Lenses."
? In 1971, Bausch & Lomb took the lead in producing and selling soft lenses
? In 1981, CIBA Vision launched its first pair of tinted lenses
? In 1982, CIBA Vision launched its first pair of tinted lenses. A pair of cosmetic lenses
? 1986, Johnson & Johnson launched disposable lenses
? 1987, Bausch & Lomb first sold contact lens total care solution (MPS)
? 1989 , FDA limited long-term wear to 7 days
? In 1990, the optometry community proposed the concept of regular replacement of contact lenses
The current situation of CL
? Market: There are about 80 million people with myopia in Chinese cities, and about 3 million insist on wearing glasses, accounting for 4.
? 30% of wearers stop wearing them every year. The reasons are: fear of trouble: 40%, discomfort: 40%
? The sales growth rate of contact lenses is 15%
Lenses:
? Main brands: Bausch & Lomb, Weicome, Shibaon, Haichang, Johnson & Johnson...
? New brands: Aijue, Youshi, Baoshi Ning, Shiba, Natural Beauty, Shujie...
? Care solution: Vision Health, Bausch & Lomb, Shikang, Haichang, Weikang...
? According to the human cornea Lenses made in a shape that are directly attached to the tear layer on the surface of the cornea and are physiologically compatible with the human eye to achieve vision correction, beauty, treatment and other purposes are called contact lenses.
Basic principles of CL
? Optical properties
? CL material has a certain refractive index and good light transmittance, so CL material is made of specific Lenses made with this technology can correct a variety of refractive errors of the eye.
? Adhesion
? CL is attached to the cornea surface with the help of tear tension and will not fall off due to the movement of the eyeball during blinking.
? Adaptability
? The surface of CL is smooth, and the curved surface design is easy to adapt to after reasonable matching, without obvious discomfort.
? Oxygen permeability
? The allowable oxygen transmission ratio of soft lenses: 8-10
? The critical value of corneal oxygen demand: 6
? Normal wearing of glasses will not cause hypoxia in the eyes (eyes open)
? Metabolic
? Helps to discharge metabolites under the lenses
CL indications
? Correction of vision: myopia (especially high myopia), hyperopia, astigmatism, anisometropia (the diopter difference between the two eyes is more than 2.50D)
? Beauty: Color films are used to change the color of the cornea, cover corneal white spots, etc.
? Treatment:
? Reduce sutures, reduce scar formation after surgery, protective effect
? Sustained release administration, improve the bioavailability of eye drops
? To treat amblyopia, use opaque lenses to cover the good eye and exercise the affected eye
Occupational needs:
? Avoid frame obstruction: athletes, drivers, outdoor workers
? To prevent water vapor from blurring the lenses when breathing: doctors, chefs and other people who wear masks when working
? Appearance requirements: actors, program hosts
Advantages of CL
? Natural vision: every time the frame increases by 0.25D, the image will be enlarged or reduced by 0.5. For patients with anisometropia, due to excessive binocular aberration, the fusion of the eyes will be hindered, so the CL image is close to reality.
? Broad field of view: The field of view is correspondingly reduced due to the limitation of the frame, and the CL field of view is wide
? Comfortable to wear: the frame is loaded with weight, contact dermatitis, and the frame is worn from cold to hot environments. Steam condenses, causing blurred vision
? Easy to wear: the frame slides down from time to time on the bridge of the nose and needs to be pushed by hand. If it is accidentally dropped, the glass piece is easily broken
? Beautiful: avoid The frame covers the eyes and facilitates communication. The shape and side width of the frame change the face shape of the wearer. Wearing it for a long time may easily cause the bridge of the nose to collapse and the eyeballs to bulge.
? Safety: When frame wearers (glass lenses) encounter violence, broken lenses can easily cause eyeball damage.
How long should the lenses be worn at one time?
? Daily wear: no more than 16-18 hr a day
? Flexible wear: no more than two nights a week (non-continuous)
? Long-term wear: usually no more than 7 days
The current optometry industry recommends daily removal and wear
The time limit from use to disposal of lenses
? Traditional lenses: Soft lenses are usually 6-12 months
? Regular replacement lenses: 1 week - 1 month - half a year
? Disposable lenses.
The texture of the lens is usually evaluated by elastic modulus
? Hard lens
? Breathable hard lens
? Silicone lens
? Soft lenses
Weight percentage of water content after the lens is fully hydrated
? Soft lenses: low water content 30-50
Medium Moisture content 51-60
High moisture content 61-80
Usually refers to the measurement parameter of the geometric center thickness of the soft lens
? Ultra-thin type: 0.09 mm
The maximum linear distance between two points on the edge of the lens
? Breathable hard lenses: 8.0mm-10.5mm
? Soft lenses: 13.5mm-15.0 mm
A quantitative written basis for defining the type of refractive error in the wearing eye
? Spherical lenses: for eyes with no astigmatism or low astigmatism
? Astigmatism lenses : For use with astigmatism that cannot be corrected by spherical lenses
? Bifocal lenses: For use with presbyopia
? Vision correction lenses
? Cosmetic lenses
? Therapeutic lenses
? Color-blind lenses
Ideal contact lenses should have the following conditions:
? Comfortable to wear
? Clear vision
? Good oxygen permeability
? Non-toxic
? Easy to operate
? Easy maintenance
? Durable
Multi-parameters
Base curve
? The base curve of the lens should be slightly larger than the corneal curvature by 5-10, which is beneficial to metabolism
– If the base curve of the lens is too small, it is called a tight fit
– If the base curve of the lens is too large, it is called a loose fit
? Moisture content: The number of water molecules in the contact lens lens Content
? The moisture content of soft lenses is generally between 30 and 80
? The moisture content of soft lenses is expressed as a percentage:
Moisture content = ( Water weight in the lens/total weight of the lens) 100
? Water is the carrier of oxygen through the soft lens material. After the oxygen molecules are dissolved in the water, they are transferred to the cornea through the lens, so the hydrophilic material is transparent Oxygen, oxygen permeability is proportional to water content
? High water content lenses: better oxygen permeability, but prone to precipitation and dry eyes.
? Low water content lenses: slightly poorer oxygen permeability, but less likely to cause precipitation and dry eyes.
? Oxygen permeability refers to the degree to which oxygen can pass through a certain membrane or other substance.
P=DK
? D: Diffusion coefficient of material
? K: Solubility coefficient of material
? Optical zone dyeing
– Softens the amount of light entering the eye
– Makes the customer’s eyes brighter
– Easier to find
? Diameter: the largest distance between two corresponding points on the edge of the lens Straight-line distance (mm)
? Optical zone diameter: the diameter of the refractive part of the lens geometric center (mm)
? The choice of diameter mainly depends on the diameter of the wearer's cornea
? The soft lens should completely cover the cornea and extend more than 1mm beyond the periphery of the cornea
? Thickness: the vertical distance between the inner and outer curved surfaces of the lens (mm)
? Thickness The lenses are slightly less comfortable to wear, but are not easily damaged, are easy to operate, and can correct low-grade astigmatism.
? Thin lenses are comfortable to wear, but are easily broken and difficult to operate.
Contact lens manufacturing process
Spin casting method
? Drop the liquid raw material into a high-speed rotating disposable mold, the amount of dripping and the direction of rotation of the mold , speed are all accurately controlled by computers to ensure that the shape, thickness, diopter and other parameters of the lens meet the design.
? During the rotation process, the liquid raw material undergoes photopolymerization reaction under the irradiation of ultraviolet rays to form a solid lens, which then undergoes edge finishing, hydration stripping, extraction, coloring, comprehensive quality inspection, and sterilization packaging. Made into finished lenses.
Molding method
? Design multiple sets of template molds according to different diopters, base arcs and diameters, and then copy one-time concave and convex molds. Inject the liquid raw material or solid blank into the concave mold for casting, and the rest of the process is the same as rotating into rows.
? Features: high efficiency, low cost, most disposable types are made using this method. The elastic modulus of the lens is larger than that of the lens using the rotating process, making it easier to operate.
? The lens is thicker, has slightly poor oxygen permeability, and has poor strength, so it is not durable. And easy to produce precipitation.
Turning method
? Use a lathe to cut the dry blank, and then hydrate it into a soft contact lens after double-sided cutting.
? Features: high production technology, high cost, good elasticity, easy to operate. Most astigmatism lenses and breathable hard lenses are made by this method.
Equivalent spherical power conversion
If the astigmatism is 0.75D, then the spherical power:cylindrical power is 3:1
If the cylindrical power is 0.75D, The spherical lens power must be greater than 2.25D
If the astigmatism is 1.00D, then the spherical lens power:cylinder lens power is 4:1
If the cylinder lens power is 1.00D, the spherical lens power must be greater than 4.00D
D = Ds 1/2 Dc
D: Equivalent spherical luminosity (CL luminosity)
Ds: Optometry spherical luminosity
Dc: Optometry cylinder power
Vertex photometry conversion (empirical method)
Optometry (D) Conversion difference (D)