What Is Prismatic Lens Therapy?
Prismatic lens therapy is one of the treatment methods used for certain eye problems, primarily diplopia, that is, double vision, as well as macular degeneration and nystagmus. Diplopia is a rare but highly disturbing eye problem that arises from disorders of the eye or nervous system. One of the most important causes of double vision is the formation of images at points other than the macula (yellow spot).
In people with double vision, prismatic lens therapy can help resolve the problem. Prismatic lenses, which help change the direction of light entering the eye, help both eyes form an image at the same point. "What is a prismatic lens?", "In which situations is a prism used?" Questions like these about prism lens therapy are addressed in the rest of this article.
What Is a Prism (Prismatic Lens)?
A prism is a refractive medium formed by two surfaces that intersect at an apex. Prisms are named according to the position of their base. Prisms bend light toward their base, and the image shifts toward the apex of the prism. The image produced by a prism is upright and virtual.
Prisms are used for diagnostic purposes, including evaluating binocular single vision, measuring the amount of deviation, assessing retinal correspondence, and identifying patients who are feigning symptoms. Prisms used for therapeutic purposes may take the form of conventional glass prisms or Fresnel prisms. As the power of glass prisms increases, their thickness, weight and aberrations increase. For this reason, they can only be mounted in spectacle lenses up to 8Δ'. Fresnel prisms take the form of a plastic membrane made of small parallel prisms with the same angle of refraction. They can be easily attached to spectacle lenses.
The therapeutic uses of prisms include strabismus, double vision (diplopia), and the presence of an abnormal head and neck posture. Especially in patients with low vision due to macular degeneration, and in patients with visual field damage from various causes, prisms may be used to shift the image onto a healthy area.
Diplopia, also known as double vision, is a vision problem characterized by seeing an object as more than one. In people with double vision, symptoms such as headache, nausea, dizziness, pain when moving the eye, and blurred or unclear vision may also occur. Eye-related problems such as ill-fitting eyeglasses or contact lenses, cataracts, astigmatism or dry eye syndrome can cause double vision. In addition, problems affecting the nerves in the brain's visual center, brain aneurysms, or more serious health conditions such as stroke can also lead to double vision. For this reason, it is important for people with double vision to first make an appointment with a doctor specialized in this field and have the necessary examinations.
Prismatic lenses are one of the optical tools commonly used in the treatment of people with double vision. Prismatic lenses, which help light entering the eye refract correctly, can be used in eyeglasses or contact lenses. The most important feature of prism lenses is their ability to bend light. Prismatic lenses help both eyes focus on the same point by slightly shifting the image of an object to eliminate the difference in images between the two eyes. In this way, the brain's visual center combines both images to form a single clear image.
Prism lenses may have different prism powers depending on the level of double vision and the patient's needs. After evaluating the degree of a person's double vision, the eye specialist determines the specific prism lens power for that person (1, 2).
What Are the Symptoms That Require Prism Use?
Prism is a commonly used treatment method for double vision (diplopia). Prism therapy is a treatment procedure in which specially designed prismatic lenses are placed in eyeglasses or contact lenses. So, what are the symptoms that indicate the need for prism therapy?, Who is prismatic lens therapy applied to? The main health problems and associated symptoms that require the use of prismatic lenses can be listed as follows (2):
Double vision (diplopia): Diplopia is a problem characterized by seeing objects as more than one. In people experiencing double vision, the use of prisms can help resolve the problem.
Strabismus: Strabismus is, in short, a condition in which both eyes cannot move in a coordinated manner (3). Prismatic lenses can help correct the coordination difference between the eyes and help focus the image on the same point.
Macular degeneration (yellow spot disease): Age-related macular degeneration (AMD) is an eye disease that occurs during the aging process. There is a structure called the macula, which enables clear vision at the center of the retina. Tissue loss or damage to the macula with age causes vision to decrease over time (4). Prismatic lenses may be effective in reducing central vision loss.
Nystagmus: Nystagmus is a vision problem in which the eyes move rapidly and uncontrollably. Eye movements may be horizontal (horizontal nystagmus), up and down (vertical nystagmus), or circular, as if drawing a circle (rotatory nystagmus). Movements generally vary between slow and fast. People with nystagmus may need to tilt or turn their heads to slow down eye movements and see more clearly (5). Prismatic lenses can help reduce the visual disturbances caused by nystagmus.
Eye tumors: Eye tumors can negatively affect eye movements and cause vision problems. Prismatic lenses can help relieve symptoms and achieve a clearer image in people with eye tumors.
The use of prismatic lenses varies depending on the type of disease, symptoms and the recommendations of the eye doctor. In all matters related to eye health, it is important to first contact a specialist ophthalmologist and create a treatment plan.
How Is the Need for a Prism Lens Diagnosed?
Prism lenses are one of the optical tools commonly used in the treatment of vision problems. Prisms can give effective results in the treatment of eye problems such as double vision (diplopia), strabismus, macular degeneration (yellow spot disease), eye tumors and nystagmus. So, how is the need for a prismatic lens diagnosed? Prism diagnosis can be made as a result of a detailed evaluation and eye examination performed by a specialist ophthalmologist. The main diagnostic methods used are as follows:
Taking a medical history: To diagnose the need for prisms, the eye doctor first conducts a detailed assessment of the patient's medical history and symptoms. At this stage, the doctor evaluates whether the patient has vision problems such as double vision or strabismus. In addition, since chronic health problems such as diabetes can cause damage to the optic nerves, the presence of any chronic illness in the patient is also taken into consideration.
Eye examination: In cases where a need for prismatic lenses is suspected, a detailed eye examination is first performed to prepare the treatment plan. During the examination, the specialist ophthalmologist conducts a detailed review of the patient's eye movements, eye alignment, visual acuity and similar matters. In addition, the anatomical structure of the eye may also be examined with the help of special devices.
Prism Assessment: In cases where a prism is needed, the diopter – that is, the prism power – is determined using trial prism lenses. Prism power expresses the optical power of the prisms to be applied.
In Which Situations Is a Prism Lens Used?
Prism lenses, created by integrating them onto eyeglass lenses, are effective optical tools used in the treatment of various eye disorders. Prism lenses are used not only for double vision (diplopia) but also for the treatment of other eye problems such as strabismus, age-related macular degeneration, nystagmus and eye tumors. Especially in people with strabismus, prism lenses can help the eyes focus on the same point. In addition, prism lenses can also be used for double vision and image disturbances that occur in other eye conditions such as age-related or traumatic macular degeneration, nystagmus and eye tumors. The optical power and characteristics of prism lenses are carefully evaluated in order to help the patient achieve the best possible image. If you are experiencing vision problems as well, do not neglect to make an appointment with a specialist ophthalmologist without losing time and to have your check-ups done.
What Are the Prism Base Directions?
Prisms bend light toward their base, and the image shifts toward the apex of the prism. Base directions allow the image to be shifted in the desired direction. Base directions are expressed with different symbols or letters, such as "Base In (BI)", "Base Out (BO)", "Base Down (BD)", and "Base Up (BU)". The main base directions used for prism application are as follows (6):
The base-out (BO) direction means that the prism lens shifts the image inward. It is commonly used especially when the eyes drift inward.
The base-in (BI) direction means that the prism lens shifts the image outward. It provides appropriate correction when the eye drifts outward.
The base-up (BU) direction means that the prism lens shifts the image downward. It is used for vertical deviations.
The base-down (BD) direction means that the prism lens shifts the image upward. It is used for vertical deviations and may help alleviate symptoms.
The base directions used in prism lenses are important for providing correct optical correction. The eye doctor determines the appropriate base direction according to the patient's needs and prepares the treatment plan.
Frequently Asked Questions
Prismatic lens therapy is one of the effective treatment methods for solving certain vision problems. Some of the questions most frequently asked about prismatic lens therapy are detailed below.
Do not neglect to have regular check-ups for your eye health as well.
Prismatic lenses are optical tools used in the treatment of vision problems such as double vision (diplopia), macular degeneration and strabismus.
Prismatic eyeglasses are specially designed eyeglasses that differ from standard eyeglasses in that they contain prisms. During prismatic lens therapy, the prismatic lenses placed in the eyeglasses change the direction of light, helping the image reach the eye properly.
Prismatic eyeglasses are generally used in situations where the eyes do not work in coordination.
The eye specialist determines the prism power and base direction during the eye examination by using certain tests.
It is important for people with vision problems to attend regular check-ups. During an eye doctor visit, if the specialist notices a change in the degree of the vision problem, they may prescribe new eyeglass lenses.
