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

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

3. 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.

4. 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.

5. 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.

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

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

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

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

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

11. 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

12. 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).

13. Astigmatism:

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

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

16. 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.

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

18. 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)

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