What is the difference between myopia and hyperopia?

Myopia (nearsightedness) occurs when the eye is too long, causing light to focus in front of the retina. Distance vision is blurred, near vision is clear. It is corrected with minus (concave) lenses. Hyperopia (farsightedness) occurs when the eye is too short, causing light to focus behind the retina. Near vision is most affected, especially as accommodative reserve decreases with age. It is corrected with plus (convex) lenses.

What is astigmatism and how is it corrected?

Astigmatism is caused by an uneven curvature of the cornea or lens, producing different focal points for different meridians. Vision is blurred at all distances. It is corrected with cylindrical lens power specified by a magnitude and an axis (0-180°). The prescription notation includes sphere, cylinder, and axis, for example -1.00 -1.25 x 180.

What is presbyopia and when does it typically develop?

Presbyopia is the age-related loss of accommodation caused by progressive hardening of the crystalline lens. It typically becomes symptomatic in the mid-40s and affects virtually everyone eventually. It is corrected with a reading addition (add power) delivered through reading glasses, bifocals, or progressive lenses. The required add power increases from approximately +1.00 D at age 45 to about +2.50 D by the mid-50s.

Refractive Errors: CPO Exam Study Guide

What Are Refractive Errors?

Refractive errors occur when the eye cannot focus light precisely on the retina, resulting in blurred vision. They are the most common cause of correctable vision impairment worldwide and the primary reason most patients seek eye care. As a CPO, understanding the four main refractive errors helps you explain findings, assist with pre-testing, and anticipate the physician's correction goals.

Myopia (Nearsightedness)

Myopia occurs when the eye is too long relative to its focusing power, causing light to converge in front of the retina rather than on it. The result is clear near vision but blurred distance vision.

Corrected with minus (concave) lenses
Prevalence is increasing globally, particularly in East Asia
High myopia (above -6.00 D) increases risks of retinal detachment, glaucoma, and myopic maculopathy
Onset typically in childhood, often stabilizes in the mid-20s

Hyperopia (Farsightedness)

Hyperopia occurs when the eye is too short or the cornea is too flat, causing light to converge behind the retina. Young patients can compensate through accommodation (the lens flexing to add focusing power), but this effort causes eyestrain and headaches. Older patients lose this accommodative ability and experience blurred vision at all distances.

Corrected with plus (convex) lenses
Mild hyperopia may be fully compensated by a young patient's accommodation
High hyperopia increases risk of angle-closure glaucoma due to a naturally smaller anterior segment
Accommodative esotropia in children can result from uncorrected hyperopia

A child with uncorrected hyperopia may have seemingly normal distance and near vision because they accommodate fully to compensate. However, the constant accommodation effort can cause amblyopia and esotropia. This is why children need comprehensive eye exams even if they do not complain of blurred vision.

Astigmatism

Astigmatism occurs when the cornea or lens has an uneven curvature, like a football rather than a basketball. Different meridians of the eye have different focusing power, so no single focal point exists on the retina. Vision is blurred at all distances.

Corrected with cylinder power in the spectacle prescription
Specified by sphere, cylinder, and axis (e.g., -2.00 -1.50 x 090)
With-the-rule astigmatism: steeper vertical meridian (axis near 90°), more common in children and young adults
Against-the-rule astigmatism: steeper horizontal meridian (axis near 180°), more common in older adults
Oblique astigmatism: steepest meridian at an oblique axis (not near 90° or 180°)

Presbyopia

Presbyopia is the age-related loss of accommodation (the ability to change focus for near objects) caused by progressive hardening of the crystalline lens. It becomes symptomatic in the mid-40s and affects virtually everyone eventually.

Corrected with a reading addition (add power) to the distance prescription
Delivered via reading glasses, bifocals, progressive lenses, or multifocal contact lenses
The required add power increases with age: typically +1.00 at 45, progressing to approximately +2.50 by the mid-50s

Presbyopia is not a disease — it is a normal, universal aging change. Patients often feel distressed when first diagnosed. Reassuring them that it is a normal process that affects everyone and is easily corrected helps reduce anxiety.

Comparing the Four Refractive Errors

Error	Problem	Blur Pattern	Correction
Myopia	Eye too long	Distance blurred, near clear	Minus lens
Hyperopia	Eye too short	Near blurred (or all distances in older patients)	Plus lens
Astigmatism	Uneven curvature	Blurred at all distances	Cylinder lens
Presbyopia	Stiff lens, no accommodation	Near blurred in middle-aged adults	Add power (bifocal/progressive)

Confusing presbyopia with hyperopia. Both cause difficulty with near vision, but they have different mechanisms. Presbyopia is loss of accommodative flexibility from a stiffened lens; hyperopia is a structural mismatch where the eye is too short. A myopic patient can still develop presbyopia and may actually prefer their near vision without their distance glasses as they age.

Key Takeaways

Myopia: eye too long, distance blur, corrected with minus lenses
Hyperopia: eye too short, near blur (or all distances), corrected with plus lenses
Astigmatism: uneven corneal curve, blur at all distances, corrected with cylinder power
Presbyopia: stiff lens from aging, near blur in 40s+, corrected with add power
High myopia increases risk of retinal detachment and maculopathy
High hyperopia increases angle-closure risk and can cause accommodative esotropia in children