1. History of Contact Lens Development
Development of materials:
In 1888, glass was not promoted in clinical practice due to the difficulty of its wearer in adapting.
In 1937, the hard mirror was made of polymethyl methacrylate (PMMA), which had high hardness and low water content.
In 1971, PHEMA, a hydrophilic material, became very soft when in contact with water.
In 1977, the breathable semi hard mirror RGP (CAB, SMA, FSA) was located between hard and soft mirrors, with a significant increase in oxygen permeability.
2. Development of processing technology:
1. Rotary forming process:
The lens mold is made by computer program control. This process involves dropping multiple purified liquid raw materials into this high-speed rotating disposable mold. The amount of dripping, as well as the direction and speed of mold rotation, are accurately controlled by a computer in all directions to ensure that the shape, thickness, and refractive index of the lens meet the design requirements. During the rotation process, liquid raw materials undergo photopolymerization reaction under ultraviolet radiation, forming solid lenses. After edge finishing, hydration and film removal, extraction, coloring, comprehensive quality inspection, and disinfection packaging, the finished lenses are produced.
Features: Smooth surface, soft and thin texture, comfortable to wear, but poor correction effect for astigmatism.
2. Cutting forming process:
Use a lathe to cut the dry blank, then double cut and water synthesize soft contact lenses.
Features: High production process, high cost, good elasticity, and easy operation. Most astigmatic lenses and breathable hard lenses are made using this method.
3. Molding process:
Design multiple sets of template molds based on different diopters, base arcs, and diameters, and then replicate one-time concave and convex molds. Inject liquid raw materials or solid blanks into the concave mold for casting and pressing, and the other processes are the same as rotating into rows.
Features: High efficiency, low cost, and most discarded shapes are made using this method. The elastic modulus of the lens is greater than that of the rotating process lens, making it easier to operate and plastic. Due to the cutting formed lens, two to three types of base arcs can meet the usual corneal curvature, making it more comfortable to wear. The lenses are thick, have slightly poor oxygen permeability, and have poor strength, so they are not durable.
4. Comprehensive forming process: rotary cutting process, die pressing cutting process.
3. The basic principles and indications of contact lenses
Basic principle:
Optics: The material of contact lenses has good light transmittance and stable refractive index. Therefore, using specific techniques to make contact lens materials into lenses can correct various refractive errors in the eyes.
Adhesion: Contact lenses attach to the surface of the cornea through the tension of tears. When the inner curvature of the lens is similar to the shape of the cornea to a certain extent, the lens can stably adhere to the surface of the cornea and will not fall off due to blink, eye rotation, or whole body movement.
Adaptability: The surface of contact lenses is smooth and the curved surface design is reasonable, making it easy to adapt after wearing without significant discomfort.
Oxygen permeability: Soft and semi hard lenses have high oxygen transmittance, which can maintain normal oxygen supply to the eyes.
Metabolism: Contact lenses move slightly with the blinking movement of the eyelids, helping to expel metabolites under the lenses. It has little effect on corneal metabolism.
4. Indications (who needs or needs to wear contact lenses)
<Corrected vision
1. Myopia, especially high myopia.
2. Hyperopia, especially high hyperopia.
3. Astigmatism, especially irregular astigmatism.
4. Anisometropia, which means that the difference in refractive power between two eyes is more than 2.50D
5. Aphthalmic eyes, that is, those who are not suitable for intraocular lens implantation after cataract surgery.
6. Corneal conus.
<Beauty
1. Change the color of the eyes to have a makeup effect.
2. Cover corneal white spots, clouds, and other scars with colored lenses.
<Career needs
1. Athletes, drivers, business travelers, and those working outdoors can avoid the obstruction of frame glasses.
2. Photographers and microscope operators can avoid the obstruction of frame glasses during work.
3. Physicians, chefs, and others who wear masks can prevent water vapor from blurring glass lenses during breathing.
4. Actors and TV program hosts can choose contact lenses according to their appearance needs.
<Treatment
1. Corneal trauma and postoperative use of specially made collagen film contact lenses can avoid or reduce sutures, thereby preventing leakage and reducing scar formation. It can also serve as a barrier protection for the cornea in the injured facial fissure area.
2. For dry eye patients, wearing lenses soaked in lubricants and adhesives can effectively maintain the integrity and stability of the tear film.
3. As a drug delivery pathway for treating certain eye diseases, the lens can fully absorb the drug solution, which can play a role in slow-release drug delivery and improve the bioavailability of eye drops.
4. For the treatment of amblyopia, opaque lenses can be used to cover healthy eyes and exercise affected eyes. Contact lenses can also be worn according to the diopter of the affected eye to improve vision, with better image size and binocular vision than frame glasses.
5. It acts as an artificial pupil, reducing the stimulation of incoming light on the retina and increasing depth perception. Commonly used in patients with iris trauma, atrophy, or albinism.
3、 Advantages and identification principles of contact lenses
5. Advantages of Contact Lenses
Vision
1. Wearing frame glasses with an increase of 1.00D can magnify or reduce the visible image by about 2%. Patients with anisometropia wearing frame glasses may experience obstacles in binocular fusion due to excessive aberrations. The image size seen through contact lenses is close to real.
2. When patients with high refractive errors wear frame glasses, the spherical aberration and dispersion of the lenses can affect the quality of the object image. However, contact lenses, due to their tight attachment to the corneal surface, only the lenses in the pupil area receive incident light, resulting in extremely slight spherical aberration and dispersion of the lenses.
3. Patients with ametropia may experience refractive and oblique aberrations when wearing frame glasses, resulting in image distortion. However, the thickness difference of each part of the contact lens’s light incidence area is extremely small, and the visual axis is always consistent with the geometric center of the lens, so there is almost no image distortion.
Field of View
Due to the limitations of the frame and the prism effect around the lens, frame glasses reduce the wearer’s field of view accordingly. Contact lenses, on the other hand, are not covered by the frame and can always follow the eye’s movements, thus maintaining the same open field of view as normal people.
Comfortable
1. Frame glasses, especially high diopter frame glasses, place weight on the wearer’s nose bridge, and the frame often causes contact dermatitis by compressing the nose bridge and auricle, while contact lenses do not have these drawbacks.
Wearing frame glasses from cold outdoors to warm indoors can cause vapor to condense on the glass lenses, causing blurred vision. And if the surface of contact lenses is completely covered with a tear layer, there will be no condensation of water vapor.
Convenient
Frame glasses often slide down on the bridge of the nose and often need to be pushed and held by hand. When accidentally dropped to the ground, the glass lenses are easily broken, while contact lenses do not have these problems.
Aesthetics
For young contact lens wearers, it is possible to avoid frame glasses covering the eyes. Easy to communicate thoughts and emotions with the eyes.
The frame shape and edge width of frame glasses can often modify the wearer’s face shape, while contact lenses do not have this disadvantage. Wearing frame glasses for a long time often leads to the collapse of the nasal bridge and the protrusion of the eyeball. It is believed that wearing contact lenses in a timely manner can avoid this change.
Security
When frame glasses wearers encounter violent injuries, broken lenses often lead to eye penetration damage, while contact lenses are safer.
6. It is generally believed that an ideal contact lens should meet the following conditions.
1. Comfortable to wear, with no obvious foreign body sensation, irritation, or dryness after wearing. This requires a smooth surface of the lens, reasonable edge shape, and the main curvature of the inner curvature to match the anterior surface of the cornea.
2. Clear vision, good corrected near and far vision and visual contrast sensitivity after wearing. This requires good optical performance of the lens, accurate diopter, and reasonable design of the inner surface shape.
3. Good oxygen permeability, and after wearing it, the cornea can obtain higher oxygen than needed to maintain metabolism.
4. Non toxicity, the degree of polymerization of lens materials, triggering additives, and lens care products do not constitute toxicity to human eye tissue cells.
5. Easy to operate, with good lens formability, and easy to control operation when wearing glasses.
6. Easy maintenance and efficient and simple care procedures enable wearers to consistently provide standardized care for lenses.
7. Durable, lenses have sufficient tensile and fatigue strength, and are not easily damaged during wearing and care. Less adsorbed sediment on the surface of the lens
And pathogenic microorganisms, and easy to clean.
8. Multi parameter lens series with different diameters, internal curvature, thickness, water content, and large refractive range, available for different
Selection of wearing objects for.
When recommending contact lenses to customers, it is important to check if the contact lenses you recommend have some of the above advantages and introduce them to the customer.
7. Types of contact lenses
According to the wearing method: (The duration of continuous wearing of lenses is called the wearing method of lenses.)
① Daily wear refers to the wearing of lenses without sleep and with eyes open, usually for no more than 16-18 hours per day.
② Long term wear refers to the wearing of lenses while asleep, lasting for several days before removing them (usually no more than 7 days). Currently, only the Bosch Lun Pure Vision series and Shikang Day and Night series can be worn continuously for one week on the market. Other lenses, whether labeled as daily or long-term, must be cared for daily and must not be worn while sleeping.
Classification by usage cycle: (The time period from the use of lenses to their disposal is called the usage cycle of lenses.)
1. Traditional lenses with a lifespan exceeding 3 months. Soft lenses typically last 6-12 months, while breathable hard lenses typically last 1-2 years.
2. Regularly replace lenses, with a lifespan of 1 week to 3 months. Care products, also known as frequent replacement lenses, still need to be used in the usual way.
3. Disposable lenses, discarded every time the lenses are removed, usually worn continuously for no more than 7 days, without using care products. Due to the fact that lenses are only used once, they are also known as disposable lenses.
Classification by moisture content: (The weight percentage of water content in the fully hydrated lens is called the moisture content.)
Low moisture content 30% to 50%,
The medium moisture content ranges from 51% to 60%,
Classified by function:
① Vision correction lenses for patients with refractive errors, aphakia, or keratoconus.
② Beauty lenses are designed for those who wish to improve their vision, change or darken their eye color.
③ Treatment lenses are used by patients with various eye diseases who use contact lenses as a treatment method.
④ Color blind lenses are designed for patients with color blindness to improve their color change ability.
Classification by material:
The FDA in the United States has classified lens materials based on water content and ionic properties:
material quality
Low moisture content
High moisture content
Non ionic
Class I
Class II
Ionicity
Class III
Class IV
From Class I to Class IV, the adsorption capacity for precipitates gradually increases.
① For those with a high tendency to form lens deposits, low water content non ionic material lenses can be selected, and attention should be paid to shortening the lens replacement cycle and daily wearing time appropriately.
② For those who are sensitive to corneal hypoxia, high oxygen permeability (high water content, thin) lenses can be selected to increase the oxygen permeability of the lenses.
