Defectos refractivos - Dr. Jaime Hernandez

What is a Refractive Error?

Understanding Refractive Errors

• Refractive errors, or ametropia, are optical anomalies in the eye that lead to imperfect focus on the retina, resulting in poor image quality.

• Hemetropia is defined as correct measurement of light focusing on the retina. Proper focus is essential for clear image quality.

Key Structures Involved in Refraction

• The cornea, lens, and pupil are crucial for refraction; they function similarly to a camera's focusing mechanism.

• The cornea has the highest refractive power in the eye (approximately two-thirds), while the lens contributes one-third and adjusts its thickness for near or far vision.

Myopia: Causes and Treatment

Characteristics of Myopia

• Myopia occurs when distant images focus in front of the retina, creating a blurred circle of confusion that degrades image quality. Only nearby objects appear sharp to myopic eyes.

• Common causes include axial myopia (elongated eyeball) and curvature myopia (excessively curved cornea/lens). Each millimeter increase in eye length adds three diopters of refractive error.

Treatment Options for Myopia

• Treatment involves using diverging (concave) lenses to shift the focal point back onto the retina. Caution is advised with children under 10 due to their strong accommodation ability; cycloplegia may be necessary for accurate measurements.

• Parents should limit screen time for young children and encourage outdoor activities to promote healthy vision development. Tropicamide can help manage myopia progression in children.

Hyperopia: Understanding and Management

Nature of Hyperopia

• Hyperopia occurs when parallel rays from infinity converge behind the retina, often asymptomatic until around age 40 when presbyopia exacerbates symptoms due to reduced accommodation capacity. Children may experience physiological hyperopia as their eyes grow larger over time.

Treatment Strategies for Hyperopia

• Converging (convex) lenses are used to bring focal points forward onto the retina; cycloplegia may also be performed if needed to identify secondary causes of hyperopia effectively. Each millimeter decrease in eye length corresponds with three diopters of refractive error increase.

Astigmatism: Types and Corrections

Defining Astigmatism

• Astigmatism results from light rays not converging at a single point after refraction due to irregularities in either the cornea or lens shape, leading to decreased visual acuity and distorted images or lights seen by patients. It can manifest as regular or irregular astigmatism based on how light focuses relative to the retina's position.

Types of Astigmatism

• Simple myopic astigmatism occurs when some rays focus before reaching the retina while others reach it correctly; compound astigmatism sees all rays focused before it but at different points; mixed astigmatism features rays both before and behind it at varying positions; simple hyperopic astigmatism has some rays reaching behind while others hit correctly on target.

Corrective Measures

• Correction requires addressing both focal points through spherical lenses combined with cylindrical lenses tailored specifically for each type of astigmatism present within an individual's prescription needs based on severity levels observed during examination processes conducted by professionals trained accordingly.

Understanding Vision Disorders and Treatments

Overview of Common Vision Issues

• Astigmatism and Presbyopia: Astigmatism requires contact lenses for correction. Presbyopia, a condition that arises with aging, leads to difficulty focusing on close objects, often noticed when individuals start holding their phones further away after age 40.

• Myopia's Protective Effect: Patients with myopia may experience less pronounced presbyopia due to a natural physiological protection. However, this condition can worsen under bright light or fatigue.

Treatment Options for Vision Disorders

• Corrective Lenses: As individuals age, they may require stronger convex (positive) lenses to bring near vision into a comfortable working distance. Options include monofocal, bifocal, or progressive lenses.

• Visual Acuity Assessment: Visual acuity is measured using the Snellen chart during evaluations to determine the degree of vision impairment.

• Surgical Interventions: Various surgical options exist:

• Refractive surgery techniques vary in approach.

• Phaco-refractive surgery involves lens removal without cataracts present and inserting an intraocular lens to correct vision defects.

Key Takeaways for Primary Care