Diagnosis: On a Snellen chart, a person with myopia might see the top few lines clearly but struggle with smaller lines as they go further down the chart. Myopia is often indicated when the vision is worse than 20/40.
2. Hyperopia (Long-sightedness)
Definition: Difficulty seeing close objects clearly, more common in children.
Diagnosis: Hyperopia might not be as easily detected with a Snellen chart as myopia, because children often have the ability to “accommodate” or adjust their focus on the letters. Other tests, like retinoscopy, might be used for a clearer diagnosis.
3. Astigmatism
Definition: Distorted vision resulting from an irregularly curved cornea or lens.
Diagnosis: On a Snellen chart, lines might appear blurred or distorted, and lines in one direction (horizontal, vertical, or diagonal) might appear clearer than lines in another direction. This is often confirmed with detailed corneal measurements.
4. Presbyopia
Definition: Impairment of near vision in middle-aged and older adults, resulting from the loss of elasticity of the lens.
Diagnosis: Typically noticed when individuals start holding reading material farther away to see it clearly. The Snellen chart can be used for distance vision, but a reading test (like reading small print at a normal reading distance) is used for diagnosis.
5. Amblyopia (Lazy Eye)
Definition: Decreased vision in one or both eyes due to abnormal development of vision in infancy or childhood.
Diagnosis: Often detected in childhood. If one eye performs worse on a vision test (like the Snellen chart) without an obvious defect in the eye itself, amblyopia might be suspected.
6. Strabismus (Crossed Eyes)
Definition: Misalignment of the eyes, where they do not look at the same place at the same time.
Diagnosis: Visible misalignment of the eyes. Further tests are required to determine how it affects vision, including how well the eyes work together.
