A refractive error commonly affects vision, arising when the eye’s shape hinders light from focusing precisely on the retina. Uncorrected refractive error stands as the primary contributor to vision impairment, and ranks second among the causes of blindness globally.
Types of Refractive Errors
Myopia: Myopia, commonly known as nearsightedness, is a refractive error of the eye where distant objects appear blurry while close objects can be seen clearly. Myopia is defined clinically by a spherical equivalent (SE) ≤−0.5 dioptres (D). The significant rise in the occurrence of all degrees of myopia over the past three decades has prompted its characterization as an ‘epidemic’.
Hyperopia: Hyperopia, often referred to as farsightedness, is a refractive eye condition in which distant objects appear clearer than nearby ones.
Astigmatism: Astigmatism, accounting for about 13 per cent of the refractive errors of the human eye, causes blurred or distorted vision at all distances. It occurs due to abnormal curvature of the cornea or lens of the eye.
Presbyopia: Presbyopia refers to the natural decline in the eye’s ability to focus on nearby objects, which is associated with aging. This condition, also termed age-related farsightedness, leads to a gradual deterioration in the clarity of close-up vision. It commonly affects adults aged 40 and older.
Causative Factors:
Genetics: Refractive errors often run in families, indicating a genetic predisposition. For years, a genetic role in myopia has been hypothesized and is evidenced by the heightened occurrence of myopia within families, especially among children of myopic parents and individuals with myopic relatives. Additionally, there’s a stronger correlation of myopia onset among identical twins compared to fraternal twins.
Eye Anatomy: Eyes that are too long (axial myopia) or too short (axial hyperopia) can cause light to focus in front of or behind the retina, leading to myopia or hyperopia, respectively.
Corneal Shape: Irregularities in the curvature of the cornea can cause astigmatism, where light is not uniformly focused on the retina, resulting in distorted or blurred vision.
Lens Flexibility: With age, the lens of the eye becomes less flexible, leading to presbyopia, a type of hyperopia that affects near vision. This age-related change typically occurs around 40 years old.
Environmental Factors: Prolonged use of digital screens, reading in low light, or working in environments that strain the eyes may contribute to the development or worsening of refractive errors.
Medical Conditions: Certain medical conditions such as diabetes, cataracts, and retinal detachment can affect the refractive properties of the eye and may lead to refractive errors.
Eye Injuries or Surgery: Trauma to the eye or previous eye surgery can alter the shape or structure of the eye, potentially resulting in refractive errors.
Socio-economic factors: Economic obstacles to accessing eyeglasses are widespread, particularly in regions with significant poverty and limited resources. These barriers encompass both direct expenses, such as eye exams and purchasing frames and glasses, as well as indirect costs like travel expenditures and loss of income due to visits to eye care providers and optical stores.
Clinical Features
- Blurring of Vision
- Headache
- Watering of the eyes
- Squinting
- Asthenopia or eye fatigue
- Difficulty focusing
Diagnosis
Diagnosing refractive errors involves a thorough eye examination by an optometrist or ophthalmologist.
Here’s an overview:
- Visual acuity testing: Reading letters or symbols on an eye chart helps assess vision at different distances, identifying refractive errors.
- Refraction assessment: Using a phoropter, lenses are tested to find the precise correction for clear vision, with patient feedback guiding the process.
- Autorefraction: Automated instruments measure refractive errors, although subjective refinement may be needed.
- Retinoscopy: A retinoscope is used to assess refractive error by observing reflections in the eye.
- Evaluation of binocular vision: Assessing eye coordination identifies issues that may contribute to refractive errors or affect corrective lens effectiveness.
- Cycloplegic refraction: Sometimes used, especially with children, eye drops temporarily relax eye muscles for a more accurate assessment.
Management
Lifestyle Modification
- Balanced diet: Consume a balanced diet rich in minerals and vitamins, beneficial for eye health like Vitamin A, C and E, zinc and omega-3-fatty acids.
- Adequate Lighting: Ensure adequate lighting when reading, using digital devices and engaging in close up activities.
- Ergonomic Workspace: Ensure proper posture when working on computers or performing close-up tasks.
- Follow 20-20-20 rule: After 20 minutes of prolonged near work, take a 20 seconds break and look at something 20 ft away.
- Physical Exercise: Improve access to nature light, improve outdoor time and delay introducing young children to screens.
- Increase consumption of leafy greens: Leafy vegetables, such as spinach, kale, collard greens, and broccoli, are abundant sources of lutein and zeaxanthin, carotenoids crucial for eye health. These nutrients have been shown to shield the eyes from the harmful effects of blue light emitted by electronic devices.
- Keep hydrated
Non-Surgical Therapeutic Options
- Prescription Eyeglasses
- Contact Lenses: Contact lenses provide an alternative to eyeglasses for correcting refractive errors.
Surgical Treatment Options
The choice of refractive surgery depends on various factors, including the patient’s refractive error, corneal thickness, age, and overall eye health. It’s important for individuals considering refractive surgery to undergo a comprehensive eye examination and consult with an experienced eye surgeon to determine the most suitable option for their needs.
- Refractive Surgery: Refractive surgery, such as LASIK (Laser-Assisted In Situ Keratomileusis) or PRK (Photorefractive Keratectomy), reshapes the cornea to correct refractive errors permanently.
- Orthokeratology (Ortho-K): Ortho-K involves wearing specially designed rigid contact lenses overnight to temporarily reshape the cornea.
- LASEK ( Laser Assisted Sub epithelial Keratectomy): LASEK is a variation of PRK where a thinner layer of the corneal epithelium is loosened and pushed aside rather than completely removed. This allows for a quicker recovery compared to PRK.
- SMILE (Small Incision Lenticule Exrtraction): some patients due to its minimally invasive nature and potentially faster recovery often prefer SMILE.
- Phakic Intraocular Implantation: These procedures are typically carried out on individuals who are unsuitable candidates for conventional laser refractive surgery due to contraindications or those who cannot attain correction because of severe refractive errors
- Monovision: In cases of presbyopia, monovision may be employed, where one eye is corrected for distance vision and the other for near vision. This technique allows individuals to see objects clearly at different distances without the need for bifocals or reading glasses.
- Refractive Lens Exchange: This may be performed in selected patients where corneal laser surgery is not possible, or cannot achieve the desired refractive outcome
- Corneal Inlays and intercorneal implants
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