Examination Techniques for Accuracy and Efficiency Basic Review

Examination Techniques for Accuracy and Efficiency Basic Review of the Eye as an Optical System A VOSH-Florida Presentation

• • • Axial length Cornea Lens Emmetropia Myopia Hyperopia Astigmatism Accommodation Presbyopia Ocular Motility and Alignment

• Axial Length: 22 mm – 25 mm – At birth, the axial length is ~17 mm and increases by ~5 mm by age 3. – Changes of ~1 mm occur between age 3 -13, with stability usually by age 15. • Anterior Chamber Depth: – 20 year old: ~4. 0 mm – 70 year old: ~3. 5 mm – Changes are due to an increasing thickness of the lens and may result in increased myopia.

• Cornea : – There is a normal distribution of corneal refractive powers. – Most normal corneas will produce 42 – 44 diopters of refractive power (~9. 4 mm – 6. 7 mm of curvature). • Lens: – Produces ~20 diopters of refractive power by age 15.

Ocular Refractive Status • Emmetropia - incident parallel rays of light converge to focus on the retina. • Myopia - incident parallel rays of light converge to focus in front of the retina. • Hyperopia - incident parallel rays of light converge to focus behind the retina.

• Emmetropia: – Incident parallel rays of light converge to focus on the retina.

• Emmetropia – Clinical Symptoms: – Patient is happy. – Discuss sunglasses and cosmetic contact lenses!

• Myopia : – Incident parallel rays of light converge to focus in front of the retina.

• Uncorrected Myopia – Associated Clinical Symptoms : – Distance blur – Headaches/fatigue (squinting) – Photophobia/glare – Night vision problems (blur/glare) – Pseudo-diplopia (ghost images)

• Hyperopia: – Incident parallel rays of light converge to focus behind the retina.

• Uncorrected Hyperopia – Associated Clinical Symptoms : – Headaches – Fatigue when reading – Blur when reading, constant or intermittent – Distance blur later in day – Night myopia – Esotropia - accommodative strabismus

• Astigmatism: – generally defined as a non-spherical or toric anterior corneal curvature, resulting in incident rays of light having multiple points of focus: – Regular – Maximum and minimum refractive angles are separated by 90 degrees. – Irregular - Maximum and minimum refractive angles are separated by other than 90 degrees (pterygia, keratoconus, corneal scars). – Lenticular – astigmatism induced by a tilting of the crystalline lens (minimal, insignificant).

• Astigmatism:

• Uncorrected Regular Astigmatism: – Results in a Circle of Least Confusion, or the dioptric midpoint between the major lines of focus.

• Uncorrected Astigmatism – Associated Clinical Symptoms : – Headaches/fatigue (squinting) – Distance blur – Near blur – Photophobia/glare – Night vision problems (blur/glare) – Pseudo-diplopia (ghost images)

• Presbyopia – the age-related, irreversible reduction in amplitude of accommodation. – Clinically significant when the accommodative demand at the patient’s normal reading distance (~ 40 cm) is 50% of the available accommodative amplitude. – Example: ~2. 5 D accommodative demand at 40 cm with 5 D or less of accommodative facility = Presbyopia – Usually becomes symptomatic at ~40 years of age.

• Uncorrected Presbyopia – Associated Clinical Symptoms : – Near blur – Headaches/fatigue – Accommodative spasms/transient distance blurring – Intermittent diplopia/pseudo-diplopia at near

• Ocular Motility Disorders – The inability of both eyes to accurately align or maintain alignment on the target of interest. – Types: • Primary extra-ocular muscle problems – Paralytic strabismus – Convergence/Divergence infacility/insufficiency • Refractive-related problems – High uncorrected hyperopia (esotropia) – Significant uncorrected anisometropia (tropias/amblyopia) – Significant uncorrected antimetropia (tropias/amblyopia)

• Ocular Motility Disorders - Associated Clinical Symptoms : – Asthenopia/fatigue – Blur – distance/near – Night vision problems (blur/glare) – Diplopia – Pseudo-diplopia (ghost images) – Depth perception problems