Makindo Medical Notes

The risk is higher the more you drink, although there's no proven "safe" level of alcohol in pregnancy. Not drinking at all is the safest approach.

About Refractive Errors

Refractive Errors are common vision problems that occur when the shape of the eye prevents light from focusing directly on the retina. This results in blurred vision, which can affect daily activities such as reading, driving, and using electronic devices. Refractive errors are typically corrected with glasses, contact lenses, or refractive surgery.

Types of Refractive Errors

Cause	Details
Myopia (Nearsightedness)	Distance vision is blurred because light rays are focused in front of the fovea. Myopia is usually inherited and often discovered in childhood. It often progresses throughout the teenage years when the body is growing rapidly.
Hyperopia (Farsightedness)	Near vision is blurred because light rays are focused behind the fovea. It can also be inherited. Children often have hyperopia, which may lessen in adulthood. In mild hyperopia, distance vision is clear while near vision is blurry. In more advanced hyperopia, vision can be blurred at all distances.
Astigmatism	Refraction is unequal in different parts of the eyeball, usually occurring when the front surface of the eye, the cornea, has an asymmetric curvature. Normally, the cornea is smooth and equally curved in all directions, allowing light to focus equally on all planes.
Presbyopia	Age-related diminution in near vision, typically noticed around the age of 40 years. The lens of the eye becomes more rigid and does not flex as easily, resulting in a loss of focusing ability and difficulty reading at close range. This normal aging process of the lens can also be combined with myopia, hyperopia, or astigmatism. There is no way to slow down or reverse presbyopia.

Causes

Refractive errors are primarily caused by abnormalities in the shape of the eye, which affect how light is bent (refracted) as it enters the eye. Key causes include:

• Genetic Factors: Family history plays a significant role in the development of refractive errors.
• Environmental Factors: Prolonged near work, such as reading or screen time, may contribute to the development of myopia.
• Eye Anatomy: Abnormalities in the curvature of the cornea or lens, or the length of the eyeball, can lead to myopia, hyperopia, or astigmatism.
• Age: Presbyopia is an age-related condition affecting the lens's flexibility.
• Health Conditions: Certain conditions like keratoconus can cause irregular astigmatism.

Clinical Presentation

• Myopia: Difficulty seeing distant objects clearly, such as road signs while driving.
• Hyperopia: Difficulty focusing on near objects, leading to eye strain and headaches during close work.
• Astigmatism: Distorted or blurred vision at all distances due to irregular curvature of the cornea or lens.
• Presbyopia: Difficulty reading small print or seeing objects up close, typically requiring reading glasses.

Differential Diagnosis

• Cataracts: Clouding of the lens leading to blurred vision.
• Glaucoma: Increased intraocular pressure causing vision loss.
• Keratoconus: Progressive thinning and bulging of the cornea, leading to irregular astigmatism.
• Macular Degeneration: Damage to the central part of the retina, causing loss of central vision.
• Retinal Detachment: Separation of the retina from its underlying support tissue, leading to sudden vision loss.

Investigations

Accurate diagnosis of refractive errors involves a combination of visual assessments and imaging studies:

• Sight Testing:
  • Visual Acuity Test: Measures the clarity of vision at various distances using a Snellen chart.
  • Refraction Test: Determines the precise prescription needed to correct vision using a phoropter.
  • Slit-Lamp Examination: Assesses the structures at the front of the eye, including the cornea, lens, and iris.
  • Tonometry: Measures intraocular pressure to rule out glaucoma.
• Additional Tests:
  • Ocular Coherence Tomography (OCT): Provides detailed images of the retina and other ocular structures.
  • Corneal Topography: Maps the surface curvature of the cornea to detect irregularities.
  • Pachymetry: Measures corneal thickness, useful in evaluating conditions like keratoconus.

Management

Refractive errors are typically managed through corrective lenses, surgical interventions, or a combination of both to restore clear vision:

• Glasses and Contact Lenses:
  • Glasses are the most common and non-invasive method to correct refractive errors.
  • Contact lenses provide an alternative for those who prefer not to wear glasses or require more precise vision correction.
• Refractive Surgery:
  • Laser in Situ Keratomileusis (LASIK): Uses a laser to reshape the cornea, correcting myopia, hyperopia, and astigmatism.
  • Photorefractive Keratectomy (PRK): Similar to LASIK but involves reshaping the cornea's surface without creating a flap.
  • LASIK Alternatives: Includes procedures like LASEK and SMILE, which offer different approaches to corneal reshaping.
• Orthokeratology:
  • Non-surgical method using specially designed contact lenses to temporarily reshape the cornea overnight, providing clear vision during the day without the need for glasses or contacts.
• Phakic Intraocular Lenses:
  • Implanted lenses used in cases where laser surgery is not suitable, providing permanent correction of refractive errors.
• Regular Eye Examinations:
  • Essential for monitoring changes in refractive status, especially in children and adolescents whose eyes are still developing.
  • Helps in early detection and management of any associated ocular conditions.

Prognosis

The prognosis for individuals with refractive errors is generally excellent with appropriate corrective measures:

• Corrective Lenses: Provide immediate improvement in vision quality, with adjustments as refractive status changes over time.
• Refractive Surgery: Offers long-term correction with high satisfaction rates, though it carries risks like dry eyes, glare, and potential need for retreatment.
• Orthokeratology: Effective for temporary correction and slowing myopia progression in children, with minimal risks.
• Regular Monitoring: Ensures timely updates to prescriptions and detection of any developing ocular conditions.

Revisions

• Last updated: 27/04/2024

References

• American Optometric Association. Refractive Errors. Available at: https://www.aoa.org
• National Eye Institute. Types of Refractive Errors. Available at: https://www.nei.nih.gov.
• Kahn, J. M., & Khan, P. M. (2015). Clinical Ophthalmology: A Systematic Approach. Elsevier Health Sciences.
• Werner, J. S., & Crawford, M. P. (2012). Refractive Surgery. Springer.
• Seidel, T., et al. (2018). Clinical Procedures in Primary Eye Care. Elsevier Health Sciences.
• Flaxman, S. R., et al. (2017). Global Causes of Blindness and Distance Vision Impairment 1990-2020. Ophthalmology.