quiz 2

• Emmetropia is the refractive state of an eye where parallel rays of light entering the eye are focused on the retina
• Emmetropization occurs via an active mechanism where defocus drives the growth of the eye
• Genetic factors and emmetropization both influence the growth of the eye's axis
• Hypermetropia, also known as Hyperopia, Long-sightedness, or far-sightedness, is a vision condition where distant objects are seen more clearly than close ones
• Types of Hypermetropia:

  • Simple hyperopia: caused by biological diversity
  • Pathological hyperopia: caused by abnormal eye development, disease, or trauma
  • Functional hyperopia: caused by paralysis interfering with the eye's ability to accommodate
• Severity of Hypermetropia:

  • Low Hypermetropia: refractive error is less than or equal to +2.00 diopters (D)
  • Moderate Hypermetropia: refractive error is more than +2.00 D up to +5.00 D
  • High Hypermetropia: refractive error is beyond +5.00 D
• Causes of Hypermetropia:

  • Genetics: strong family history increases susceptibility
  • Environmental Factors: prolonged close work or reading, especially in low light
  • Age: as the eye ages, the lens loses flexibility, making it harder to focus on close objects
• Signs and Symptoms of Hypermetropia:

  • Blurred Vision, especially when focusing on close objects
  • Eyestrain: tiredness or discomfort after prolonged close work
  • Headaches, particularly during or after tasks requiring near vision
• Causes of Myopia:

  • Structural defects in the retina such as small-sized eyeball, non-circular lenses, flatter cornea, defective blood vessels, weakness in ciliary muscle, changes in refractive index of the lens, alterations in lens position or absence
• Types of Myopia:

  • Axial Myopia: due to a relatively long axial length
  • Curvature Myopia: due to decreased radius of curvature of refractive surfaces
  • Index Myopia: due to an increase in refractive index of the lens nucleus
  • Displacement of Refractive Element: due to forward displacement of the lens
• Symptoms of Myopia:

  • Blurred vision for distant objects
  • Squinting
  • Eye strain
  • Difficulty seeing at night
  • Holding objects close to your face
  • Headaches
• Treatment for Myopia:

  • Glasses
  • Contact Lenses
  • Refractive Surgery
  • General Instructions
• Astigmatism is a common eye problem that can make vision blurry or distorted
• Causes of Astigmatism:

  • Irregular shape of the cornea or lens
• Types of Astigmatism:

  • Myopic Astigmatism: focusing before the target
  • Hyperopic Astigmatism: beyond the mark
  • Mixed Astigmatism: a blend of farsightedness and nearsightedness
• Symptoms of Astigmatism:

  • Blurry vision or areas of distorted vision
  • Eyestrain
  • Headaches
  • Squinting
  • Difficulty with night vision
• Treatment for Astigmatism:

  • Eyeglasses
  • Refractive Surgery (LASIK, SMILE)
  • Contact Lenses (toric soft lenses, RGP)
• Anisometropia is a visual condition in which there is a significant difference in refractive error between the two eyes
• Anisometropia:

  • A visual condition where two eyes have significantly different refractive power
  • One eye focuses light differently than the other, leading to blurred vision
  • Each eye presents a different refractive error or there is a difference of 1 or more dioptres between the two eyes
  • Symptoms include blurred vision, difficulty focusing, double vision, headaches, squinting, and poor depth perception
  • Causes can be genetic, congenital factors, eye shapes, developmental issues, eye injury, acquired factors, eye diseases, and surgery
• Treatment options for anisometropia:

  • Eyeglasses are common for mild to moderate cases
  • Contact lenses sit directly on the cornea, providing clearer vision and a wider field of view compared to glasses
  • Bifocals or multifocals address near and farsightedness within a single lens
  • Additional solutions include atropine eye drops for children with anisometropia and amblyopia, vision therapy exercises, LASIK or other refractive surgeries, and intraocular lens implants
  • Surgical options like intraocular lens implants can correct refractive errors in each eye
• Fun facts about anisometropia:

  • Pirates may have used eye patches to manage blurry vision from anisometropia
  • Research on adaptive lenses is ongoing to offer personalized solutions
  • Anisometropia is not exclusive to humans; animals like chameleons and flatfish also have different levels of vision in each eye
• Aphakia:

  • Absence of the crystalline lens in its anatomical position, leading to extreme hyperopia
  • Symptoms include blurred vision for both distance and near vision, deep anterior chamber depth, iridodonesis, and small optic disc
  • Causes can be congenital, medical conditions, injury
• Treatment for aphakia:

  • Spectacles advised for 6 weeks after surgery but have disadvantages like image magnification, spherical aberration, and restricted visual field
  • Contact lenses neutralize the disadvantages of spectacles and offer advantages like less image magnification, fewer aberrations, increased visual field, better physical coordination, and cosmetic appeal
  • Secondary intraocular lens implantation can provide advantages like minimal image magnification, absence of aberration, restoration of normal peripheral vision, and excellent physical education
• Pseudophakia:

  • Replacement of the natural crystalline lens by a synthetic intraocular lens (IOL)
  • Types of IOL include polymethyl methacrylate (PMMA), silicon, and acrylic
  • Calculation of IOL power involves axial measurement by A-scan, keratometry, and standard calculations by formulas
• Presbyopia:

  • The eye loses the ability to change its focus, affecting close-up vision
  • Symptoms include blurring of vision, eyestrain, headache, reading materials held further away, and the need for more light
  • Generally starts developing around ages 38-42 and worsens until the mid-60s
• Treatment for presbyopia:

  • Spectacles with corrective convex spherical lenses
  • Surgical options like Conductive Keratoplasty
  • Contact lenses with various types of bifocal lenses
  • Eye drops like pilocarpine to improve depth of focus and provide clearer close-up vision