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REFRACTIVE ERROR
Under normal Circumstances all the structures of the eye in the path of light rays allow it to focus on the retina thus creating a sharp image that is transmitted to the brain. There are several structures within the eye that helps see an image clearly.
- Cornea: It is a dome shaped tissue forming the front part of the eye. It allows light to enter the eye to begin the process of seeing images.
- Lens: A flexible, transparent tissue rests behind the iris and the pupil. The lens is flexible and it changes it curved shape to focus on the object, people and nearby scenes.
- Retina: It helps the transmission of visual information to the brain through the optic nerve. A light-sensitive tissue, a sensory membrane composed of several layers and contains two special cells called photoreceptors.
In certain cases, the light is prevented from focusing on the retina due to the shape of the cornea, the aging of the lens or the length of the eyeball – this can lead to refractive errors.
Types of Refractive Errors
- Myopia
Also called near-sightedness, is a condition where the light rays tend to focus in front of the retina instead of focusing on the surface. It is caused because the cornea or the lens is too thick or curved for the length of the eye ball. People suffering from near- sightedness can see clearly what’s near but have difficulty with distance seeing. It is a condition that worsens with during childhood and runs in families.
Treatment: Refractive vision correction, glasses, contact lenses. Recently certain drops are available which when started at an appropriate age in children can lead to slowing the progression of myopia.
- Hyperopia
A common vision problem affecting a fourth of the population, this condition is called farsightedness, a disorder in which people are not able to focus on objects that are close by. It is the opposite of near-sightedness, in this condition, the length of the eyeball is short and the light appears to focus behind the retina instead of front of the retina. Distant objects appear to be clearer than close objects.
Treatment: Refractive vision correction, glasses and contact lens.
- Astigmatism
Astigmatism is a refractive error that could occurs alongside Myopia and Hyperopia. It is a condition owing to the cornea being irregularly shaped in the form of a rugby ball or a refractive error in the lens- this prevents the light rays from being focused on the retina.
Treatment: Refractive vision correction, glasses and contact lens.
- Presbyopia
In young people, the lens is elastic, and the ciliary muscles adjust the shape of the lens to focus on the images. However with age this ability of the eye to focus images sharply is lost leading to blurred vision near vision or Presbyopia.
Causes of Refractive Error
Refractive errors occur when the shape of your eye prevents light from focusing correctly on the retina, resulting in blurred vision. The main causes include:
- Eye Shape: The overall shape of the eye can affect how light is refracted. An elongated eye causes myopia (nearsightedness), while a shorter eye causes hyperopia (farsightedness).
- Cornea Shape: If the cornea is irregularly shaped, it can lead to astigmatism, where light is scattered instead of focused on a single point on the retina.
- Aging Lens: As we age, the eye’s lens can become less flexible and lose its ability to change shape easily, leading to presbyopia (difficulty in focusing on close objects).
- Genetics: Refractive errors can be hereditary. If your parents have refractive errors, you are more likely to develop them.
- Environmental Factors: Prolonged near tasks like reading or computer work, especially during childhood, may contribute to the development of myopia.
- Other Eye Conditions: Certain eye conditions and health issues, like diabetes or eye injuries, can also cause or exacerbate refractive errors
Refractive errors can cause a variety of vision problems. Common symptoms include:
- Blurred Vision: Difficulty seeing clearly at various distances. For example, myopia causes difficulty seeing distant objects, while hyperopia makes it hard to see close objects.
- Double Vision: Seeing two images of a single object, also known as diplopia.
- Eye Strain: Discomfort or fatigue in the eyes, especially after reading, using a computer, or performing other visual tasks.
- Headaches: Frequent headaches, particularly after prolonged periods of reading or focusing on near tasks.
- Squinting: Frequently squinting to try to see more clearly.
- Difficulty Seeing at Night: Problems with night vision, including difficulty seeing while driving at night.
- Halos Around Lights: Seeing halos or glare around lights, especially at night.
- Frequent Changes in Prescription: Needing frequent updates to your glasses or contact lens prescription.
Refractive errors are diagnosed through a comprehensive eye examination, which includes the following tests:
- Visual Acuity Test: This test measures how clearly you can see at various distances. You’ll read letters from a chart (Snellen chart) placed at a specific distance to determine your visual acuity.
- Refraction Assessment: Using a phoropter or a retinoscope, the eye doctor measures how light bends as it enters your eye. This helps determine the exact prescription needed for glasses or contact lenses.
- Autorefractor Test: This automated device measures how light is changed as it enters your eye, providing an initial prescription that the doctor may fine-tune.
- Keratometry: This test measures the curvature of the cornea, which helps in diagnosing astigmatism. A keratometer is used to assess how light is reflected from the surface of your cornea.
- Retinal Exam: The doctor examines the retina and optic nerve using special instruments to ensure there are no other underlying eye conditions affecting your vision.
- Slit-Lamp Examination: This test uses a microscope with a bright light to examine the front part of the eye, including the cornea, iris, lens, and anterior chamber.
Treatments for Refractive Error
Refractive errors can be effectively treated with various methods to improve vision. Common treatments include:
- Eyeglasses: The simplest and most common way to correct refractive errors. Lenses in the glasses help to refocus light correctly onto the retina, providing clear vision.
- Contact Lenses: These are worn directly on the eye and offer a wider field of vision compared to glasses. Different types of contact lenses are available, including daily, monthly, and extended-wear lenses.
- Refractive Surgery: Surgical options like LASIK (Laser-Assisted in Situ Keratomileusis), PRK (Photorefractive Keratectomy), and LASEK (Laser-Assisted Sub-Epithelial Keratectomy) reshape the cornea to correct the refractive error. These procedures can reduce or eliminate the need for glasses or contact lenses.
- Orthokeratology (Ortho-K): Specially designed rigid contact lenses are worn overnight to temporarily reshape the cornea, allowing for clear vision during the day without the need for glasses or contact lenses.
- Lens Implants: In some cases, intraocular lenses (IOLs) can be implanted in the eye to correct severe refractive errors. This option is often considered for people who are not good candidates for laser surgery.
Each treatment option has its advantages and considerations. Schedule a consultation with us to determine the most suitable treatment for your specific refractive error and lifestyle.
Frequently Asked Questions
Yes, refractive errors can be hereditary. If your parents have refractive errors, you are more likely to develop them as well.
Yes, children can have refractive errors. Symptoms include difficulty reading, squinting, sitting too close to the TV, and frequent headaches. Regular eye exams are essential for early detection and treatment.
Refractive errors can change over time, especially during childhood and adolescence. Regular eye exams are important to monitor changes and update prescriptions as needed.
To reduce eye strain, follow the 20-20-20 rule: every 20 minutes, look at something 20 feet away for 20 seconds. Adjust your screen brightness, ensure proper lighting, and take regular breaks.
Regular eye exams and proper eye care are crucial for maintaining good vision and managing refractive errors. Schedule an appointment with us for personalized care and treatment options.