👓 Refractive errors are the most common cause of visual impairment worldwide.
They are easily correctable but, if unrecognised, can affect education, driving, and quality of life.
With proper management (glasses, contact lenses, or surgery), prognosis is excellent.
📍 About Refractive Errors
Refractive errors occur when the shape of the eye prevents light from focusing directly on the retina.
This leads to blurred vision, affecting near and/or distance tasks.
They are not diseases but optical imperfections of the eye.
🔎 Types of Refractive Errors
| Type |
Details |
| Myopia (Nearsightedness) |
Light focuses in front of the retina. Distance vision is blurred.
Often inherited; discovered in childhood; may progress in teenage years.
⛔ Risk: Retinal detachment in high myopia. |
| Hyperopia (Farsightedness) |
Light focuses behind the retina. Near vision is blurred, distance often clearer.
Common in children, may lessen with age.
⛔ Risk: Angle-closure glaucoma. |
| Astigmatism |
Irregular corneal or lens curvature → unequal refraction.
Causes blurred or distorted vision at all distances. |
| Presbyopia |
Age-related lens stiffening → reduced near focus.
Onset ~40 years; universal and progressive.
Requires reading glasses or multifocals.
🕒 Physiological, not pathological. |
⚙️ Causes
- Genetic: Family history is key.
- Environmental: Prolonged near work may contribute to myopia.
- Ocular anatomy: Corneal curvature, lens shape, or eyeball length abnormalities.
- Age: Presbyopia due to lens rigidity.
- Conditions: Keratoconus causes irregular astigmatism.
🩺 Clinical Presentation
- Myopia: Blurred distance vision (e.g. road signs).
- Hyperopia: Blurred near vision, eye strain, headaches.
- Astigmatism: Distorted/blurry vision at all distances.
- Presbyopia: Difficulty with small print; arms "not long enough" for reading.
🔀 Differential Diagnosis
- Cataracts (lens opacity).
- Glaucoma (optic nerve damage from high IOP).
- Keratoconus (progressive corneal thinning).
- Macular degeneration (central retinal loss).
- Retinal detachment (sudden vision loss).
🔬 Investigations
- Visual acuity: Snellen chart.
- Refraction test: Using a phoropter or autorefractor.
- Slit-lamp: Anterior segment assessment.
- Tonometry: Exclude glaucoma.
- OCT & corneal topography: For irregular cases/keratoconus.
💊 Management
- Corrective lenses: Glasses (most common) or contact lenses.
- Refractive surgery: LASIK, PRK, SMILE → corneal reshaping.
- Orthokeratology: Overnight contact lenses to flatten cornea temporarily.
- Phakic intraocular lenses: For unsuitable surgical candidates.
- Monitoring: Regular eye exams, especially in children/adolescents.
📈 Prognosis
- Excellent with correction.
- Surgery provides long-term results but carries risks (dry eye, glare).
- Myopia progression in children can be slowed with orthokeratology or low-dose atropine.
- Presbyopia is inevitable with age but fully correctable.
📌 Exam Tip
🔑 Myopia = long eye / Hyperopia = short eye.
🔑 Presbyopia is physiological lens stiffening — not disease.
🔑 Always exclude keratoconus in irregular astigmatism.
📚 References
- American Optometric Association – Refractive Errors
- National Eye Institute – Types of Refractive Errors
- Kahn J. & Khan P. (2015). Clinical Ophthalmology. Elsevier.
- Flaxman S. et al. (2017). Global Causes of Blindness. Ophthalmology.
