Anatomy and Ammetropias PDF

GENERAL EYE ANATOMY Dr. Ariette Acevedo Rodríguez, O.D. PPO 1 OD OS WHEN LOOKING AT THE PATIENT THEIR RIGHT EYE (OD) WILL BE ON YOU LEFT SIDE AND THEIR LEFT EYE (OS) WILL BE ON YOUR RIGHT SIDE. AMETROPIAS (REFRACTIVE ERRORS) Myopia Hyperopia Astigmatism Presbyopia Simplified Reduced Sch...

GENERAL EYE ANATOMY Dr. Ariette Acevedo Rodríguez, O.D. PPO 1 OD OS WHEN LOOKING AT THE PATIENT THEIR RIGHT EYE (OD) WILL BE ON YOU LEFT SIDE AND THEIR LEFT EYE (OS) WILL BE ON YOUR RIGHT SIDE. AMETROPIAS (REFRACTIVE ERRORS) Myopia Hyperopia Astigmatism Presbyopia Simplified Reduced Schematic Eye ■ Anterior corneal surface (P)/ Simplified nodal point of the eye (N)/ Fovea (F’) ■ The distance from the simplified nodal point to the fovea is 17.0mm and the distance from the anterior corneal surface to the nodal point is 5.6mm. ■ The refractive index for air is taken to be 1.00 and the simplified refractive index for the eye (n’) is 1.333. ■ The refractive power of this reduced schematic eye is 60.0D, with its principal plane at the front surface of the cornea. Prisms ■ Prisms DO NOT stimulate accommodation. ■ The image moves towards the apex and the light goes towards the base. Minus Lens ■ Concave lens ■ Diverges light ■ Stimulates the accommodative system ■ A minus lens may cause images to appear smaller and closer to you. Plus Lenses ■ Convex lens ■ Converges light ■ Relaxes the accommodative system ■ A plus lens may cause images to appear larger and farther away from you. Emmetropia vs Ametropia ■ Emmetropia: – Parallel light rays converge to a sharp focus on the retina – When the eye is without refractive error, the plus power of the cornea and the lens refracts light to a point source on the plane of the retina. ■ Keeping the image in focus ■ Ametropia: – Any refractive condition other than emmetropia – Myopia, hyperopia, astigmatism Myopia ■ Parallel rays of light converge in front of the retina ■ Essentially the eye has too much power ■ Causes: – Steep cornea – Too much power in the lens – Long axial length ■ Patient will complain of blurry vision at distance – Has to bring material closer to see clear ■ Corrected with Concave lenses Hyperopia/Hypermetropia ■ Parallel rays of light converge behind the retina ■ Essentially the eye lacks power ■ Causes: – Flat cornea – Lens has weak power – Short axial length ■ Patient will complain of seeing blurry at near – But…accommodation can compensate hyperopia ■ Corrected with Convex lenses Astigmatism ■ Most common eye disorder ■ For correction needs a toric lens, which focuses light differently in different meridians ■ Can be simple or compound with myopia or hyperopia Astigmatism ■ CMA: Compound Myopic Astigmatism ■ CHA: Compound Hyperopic Astigmatism ■ SMA: Simple Myopia Astigmatism ■ SHA: Simple Hyperopic Astigmatism ■ MA: Mixed Astigmatism Presbyopia ■ Loss of accommodation ■ Causes: – The loss of strength of the ciliary muscle – Loss of power of the crystalline lens ■ Hardening/Stiffn ess of the lens ■ Typically presents in patients over 40 y/o