Optometry is one of the fields affiliated with ophthalmology, where the optometrist performs part of the ophthalmology services with the help of ophthalmologist and sometimes independently.
In Parsian clinic, with the cooperation of experienced optometry staff and prominent optometrists of the province, all optometry services, whether diagnostic or therapeutic, are performed.
These services include:
- measuring the extent and field of vision
- measuring the vision score and prescribing different eyeglasses including one-sight, multifocal, progressive, as well as glasses for children
- measuring and prescribing contact lenses (invisible glasses) from different types including soft lenses, hard, multifocal, hybrid, scleral, mini-sclera, and therapeutic contact lenses
- measuring and prescribing glasses with prism
- determining the chromatic vision using standard charts
- imaging different parts of eyes
- diagnosing and treating amblyopia
Prescribing contact lenses
Millions of people worldwide use contact lenses. They can be a substitute for glasses given your lifestyle and motivations.
What is a contact lens? Contact lenses also known as invisible glasses are curvy plastic planes, which are around, thin, and transparent which lie on the cornea and float on the lacrimal layer which covers the cornea. The health of cornea and the lacrimal layer is very crucial for your convenience and transparency of vision when using contact lenses. Contact lenses are used for correcting the following conditions:
- Regular astigmatism
Different types of contact lenses:
Different factories worldwide produce different types of these lenses. Generally, they are categorized into two groups including soft and hard lenses.
These lenses are rigid in terms of consistency and cannot be folded, which in terms of material of constituents, they are classified into two groups:
- PMMA contact lenses which are rarely used today.
- Hard lenses with permeability for oxygen gas (RGP): these lenses consist of a combination of plastic and other materials including silicon or fluorine polymers. In addition to preserving the shape of lens, these materials allow for passage of oxygen through the lens to the cornea. These lenses absorb moisture and have greater compatibility with cornea in comparison to other lenses. RGP lenses are the best choice for high astigmatism of cornea and keratoconus. Usage of these lenses is prescribed according to the ophthalmologist and in patients for whom soft lenses are contraindicated. This group of lenses are not flexible due to the hardness of the primary component of the lens (they cannot be folded like soft lenses), and for this reason it takes more time for the person to get used to them.
These lenses are soft and flexible, and are more tolerable and have the following types:
- Lenses for daily use: these lenses are the cheapest types which are removed before sleep and are placed again in the eyes the next morning. The maximum use of these lenses is 12-18 months, after which the lens should be replaced.
- Lenses for long-term uses: these lenses can be used throughout the day and night. This means that you can sleep with them, though at least once a week they should be removed for sterilization and cleaning. Due to their 24 hour use an increased risk of corneal infection, their usage is less recommended. The maximum allowable duration for using these lenses is one month at most.
- Disposable lenses: these lenses are more expensive but more convenient and suitable. They are removed every night and placed again the next morning, and based on the type, they are discarded on a weekly or monthly basis. With these lenses, one can sleep if required, though the lifetime of the lens decreases in return. Usage of these lenses is preferred in cases of patient sensitivity. Chromatic and toric lenses can be of this type.
- Toric lenses: these lenses can correct astigmatism. Although they do not function as efficiently as RGP lenses, they are a little more expensive than other contact lenses and have limitations for correcting astigmatism.
- Chromatic lenses: these lenses can alter the color and appearance of the eyes. Chromatic lenses themselves have different types including visible chromatic lenses, intensifier, opaque, and light filterer. Many of these lenses have only aesthetic function while some others are employed for correcting refractive defects, changing the apparent view of defective cornea, or mitigating the discomfort resulting from light especially after traumas to the eyes.
- Bandage lenses: usage of lens as bandage or dressing is performed for covering the corneal surface following trauma, surgery, or in special diseases according to ophthalmologist. This group of lenses play a significant role in healing corneal wounds thanks to their ability in maintaining oxygen and water for a long time in their tissue.
The risks of using contact lenses:
The lenses that are not sterilized and cleansed carefully increased the risk of infection. Old lenses or those that do not match the eyes may cause scratch on the eye or induction of growth of blood vessels in the cornea. Since over time the lens may warp and change the form of cornea, consistency between the contact lens and the eyes and its power should be assessed within regular time intervals by an ophthalmologist or optometrist. Since concurrent use of some eyedrops with contact lens may follow some complications, it is better that usage of eyedrops be performed according to the physician.
Who cannot use contact lenses?
In case you have the following conditions, you are not a suitable candidate for using contact lenses:
- frequent eye infections
- severe sensitivity or allergy
- treatment resistant dry eyes
- very contaminated and dusty workplace
- inability in placing and taking care of the lens
Eventually, it is recommended that you purchase lenses from relevant centers and avoid buying them from laboratories, boutiques, and even glasses shops, because they may cause serious complications for you.
The lenses which can correct myopia during the night
Orthokeratology or corneal refractive therapy is a nonsurgical treatment which corrects myopia through transient transformation of cornea. This transformation causes the light to become better focused on the retina and develop a better image (generally all of the methods for correcting refractive defects including glasses and contact lenses to LASIK do this). In this method, using rigid gas permeable contact lens, myopia is corrected through altering the curvature of cornea and reducing its convexity. The major difference between this method and surgical methods for correcting the refractive defects including LASIK is that surgical methods are permanent. However, in this method, if lens is not used, the corneal shape returns to its primary state after three days.
Although the general idea of Orthokeratology has existed from 40 years and even some treatments have been performed using this method, the recent advances in the technology of special contact lenses caused FDA in 2002 to confirm CRT lenses synthesized by Paragon company for usage during the night. This lens is the first lens confirmed by FDA to be used during the night and sleeping. These lenses correct the shape of cornea during the night and the patient can have a good vision throughout the day without any need to lenses or glasses. In Iran, these lenses have been generally called "charging lenses".
The difference between CRT and Ortho-k
In both methods, rigid gas permeable lenses are used. The difference is that firstly CRT has been confirmed by FDA to be used during the night. Secondly, CRT lenses are produced only by Paragon company, while Ortho-k lenses are synthesized by different companies.
Which groups of patients benefit most from these lenses?
These lenses can be used for all ages. FDA has allowed usage of CRT lenses for patients with myopia up to at most 6 diopter and at most 1.75 astigmatism. Many physicians use Lasik or Laser for correcting myopia, hyperopia, and astigmatism and are against this method. Nevertheless, for the small number of ophthalmologists who agree with this method the best candidates for this treatment are patients with mild myopia (at most 4 diopter or less).
How lenses are prescribed?
The ophthalmologist first specifies the curvature as well as the peaks and troughs of cornea using corneal topography. Based on the topography map of cornea, the proper lens is prescribed. Sometimes different lenses should be tested in order to achieve the most suitable lens.
How does it take for vision to be corrected?
The vision score of patients usually decreases within two weeks or less than 2-3 diopter. After this duration, the patient should use the lens during the night or some hours of the day in order for the developed correction to last. If the patient stops using the lens, the cornea gradually returns to its previous state so does the patient's vision. At early stages of corneal transformation, the patient may experience some complications such as seeing a halo which may not resolve at all in the course of the treatment. Concerning this lens, as with Lasik, the individuals with more dilated pupils experience these complications more.
LASIK or CRT?
If the goal of the patient is to get rid of glasses and lens during the day and has the conditions for using this type of lens, CRT is more preferred. However, if the patient does not like to use glasses and lens forever, they should undergo surgical interventions such as LASIK. Nevertheless, if after using the lenses the patient decides to undergo surgery, they may have to stop using the lens for several months so that the corneal finds its previous shape and then undergo the operation