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

Anterior Chamber Depth: Axial Length: 22mm – 25mm At birth, the axial length is ~17mm and increases by ~5mm by age 3. Changes of ~1mm occur between age 3-13, with stability usually by age 15. Anterior Chamber Depth: 20 year old: ~4.0mm 70 year old: ~3.5mm 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 (~9.4mm – 6.7mm 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 (~ 40cm) is 50% of the available accommodative amplitude. Example: ~2.5D accommodative demand at 40cm with 5D 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