Human Embryonic Development

Study Notes

Y inverted sutures seen during slit lamp examination are from secondary fibers, they denote boundaries of the fetal nucleus

Refractive power 20 D in unaccommodated lens 1/3 of the lens is protein 2/3 is water PH 6.9 Protein contents varies among the lens with a higher refractive index – in the nucleus (1.50) – less in the outer cortical surface (1.37) Higher refractive power in the center

Refractive Power of an Unaccommodated Lens

Refractive power refers to the ability of the lens to focus light in its natural, relaxed state.
Refractive power formula: P = 1/F, where F is the focal length of the lens.

Units and Measurement

Unit of refractive power: diopters (D).
Measurement techniques: phoropter or autorefractor in a clinical setting.

Factors Affecting Refractive Power

Lens shape and curvature
Lens material and refractive index
Pupil size and shape
Corneal curvature and refractive index

Clinical Significance

Essential in ophthalmology and optometry for diagnosing refractive errors (e.g., myopia, hyperopia, astigmatism).
Crucial for prescribing corrective lenses (e.g., glasses, contact lenses).
Important for monitoring lens changes during accommodation.

Accommodation and Refractive Power

During accommodation, the lens becomes thicker and more curved, increasing its refractive power to focus on near objects.
This process is reversible, and the lens returns to its unaccommodated state when focusing on distant objects.