Embedded Files
Refractive Errors: Myopia, Hyperopia, Astigmatism, and Their Relationship with Presbyopia
Refractive errors are eye shape abnormalities that prevent light from focusing correctly on the retina, causing blurred vision. The main types are myopia, hyperopia, and astigmatism, and after age 40–45, presbyopia ("age-related near vision loss") becomes an additional factor. Below is a detailed breakdown:
Key Facts:
Only 35% of adults are emmetropic (require no vision correction). The rest will need glasses or surgery at some point in their lives.
By 2050, 50% of the global population will have myopia (WHO estimate), largely due to lifestyle changes (e.g., screen time, reduced outdoor activity).
71% of people aged 45–65 use glasses for presbyopia (American Optometric Association).
Fórmula Dioptría
What is a Diopter and How Does it Relate to Refractive Errors?
The diopter (D) is the unit of measurement of the refractive power of a lens (or the eye) necessary to correct a visual defect. It indicates how much light must bend to focus correctly on the retina.
Diopter Formula:
The diopter is calculated with the following formula:
DIOPTER (D) = 1 / Focal Length (Meters)
Example: A lens with a focal length of 0.5 meters has:
1/0.5 = 2 Diopters (D)
Relationship with Refractive Errors:
Myopia (-D): The eye is "too long" or the cornea is "too curved," causing light to focus before the retina.
Correction: Minus lenses (e.g., -3.00 D).
Hyperopia (+D): The eye is "too short" or the cornea is "too flat," causing light to focus behind the retina.
Correction: Plus lenses (e.g., +2.50 D).
Astigmatism (cylindrical D): The cornea is irregularly shaped, causing multiple focus points.
Correction: Toric lenses (e.g., -1.50 D cyl).
Presbyopia: Loss of near focus due to aging of the lens (corrected with multifocal lenses or additional +D lenses).
Modelo ojo Emetropia
Emetropia + No-presbicia
o
Hipermetropia Leve + NO Presbicia
Emmetropia: Perfect Vision (and how it relates to refractive errors)
Emmetropia is the ideal state of the eye where incoming light is focused exactly on the retina, allowing clear vision both far and near (in young people). It is the benchmark for comparing refractive errors such as myopia, hyperopia, and astigmatism.
What is Emmetropia?
Definition: An emmetropic eye has a perfectly balanced axial length (size) and corneal curvature, allowing images to be projected clearly onto the retina without the need for corrective lenses.
Example: An emmetropic person can clearly see a tree at 6 meters and a book at 40 cm without strain.
Why is it important to understand it?
Point of comparison:
Myopia, hyperopia, and astigmatism are defined as deviations from emmetropia.
Basis for refractive surgery:
The goal of techniques such as LASIK or intraocular lenses is to bring the eye closer to an emmetropic state.
Emmetropia and Presbyopia
In young emmetropes:
The flexible lens allows them to focus on near objects (accommodation).
After age 40 (presbyopia):
They lose near vision because the lens hardens, even if they had perfect vision before.
They need reading glasses (even if they have never worn glasses before).
Modelo Ojo con Miopia
Miopía
Myopia
What is it?
Myopia occurs when the eye is too long or the cornea is too curved, causing light to focus before the retina.
Symptoms
Difficulty seeing far away (traffic signs, movie screens).
Clear near vision (reading, using the phone).
Eyestrain (in high myopia).
Causes
Genetic factors (myopic parents).
Excessive screen use (scientific debate).
Little time outdoors in childhood.
Correction
Concave (diverging) lenses
Contact lenses
Modelo ojo con Hipermetropia
Hyperopia
What is it?
The eye is too short or the cornea is too flat, so light focuses behind the retina.
Symptoms
Difficulty seeing up close (reading, sewing).
Headache or eyestrain (strain to focus).
In severe cases, blurred vision, even at distance.
Causes
Hereditary (common in children).
Aging of the lens (loss of flexibility).
Correction
Convex (converging) lenses
Contact lenses
Surgery (LASIK, intraocular lenses).
Modelo Ojo con Astigmatismo
Tipos de Astigmatismo
A. Miópico Simple
B. Miópico Compuesto
C. Hipermetrópico Simple
D. Hipermetrópico Compuesto
E. Mixto
Astigmatism
What is it?
The cornea or lens has an irregular shape (like an American football), which distorts light at multiple points.
Symptoms
Blurred or distorted vision (distance and near).
Shadows or double images.
Eye fatigue and headaches.
Causes
Genetics (common with nearsightedness/farsightedness).
Keratoconus or ectasias
Eye trauma or surgery.
Correction
Toric lenses
Toric contact lenses
Refractive surgery (toric LASIK, toric lenticular surgery, toric ICL lenses).
Emetropia+Presbicia
o
Hipermetropia+Presbicia
Presbyopia ("Farsightedness")
What is it?
Loss of near-focus ability due to hardening of the lens (starting at age 40–45).
How does it affect refractive errors?
Myopia + Presbyopia:
Myopic people can read without glasses (due to their natural near focus), but will need distance lenses.
Option: Monovision (one eye for distance, one for near) or progressive lenses.
Hyperopia + Presbyopia:
Near vision worsens, requiring bifocal or progressive lenses.
Astigmatism + Presbyopia:
Requires multifocal toric lenses or surgery with a premium IOL.
Solutions:
Progressive lenses.
Multifocal or extended-range intraocular lenses (for cataract surgery, such as phacorefractive lenses).
Laser surgery (PresbyLASIK, Presbyond, Monovision).
Google Sites
Report abuse