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Lecture 5

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McGill University
PSYC 212
Remy Allard

Lecture 5September 15 2011AccommodationoIncrease refracting power of the yeeoChanges during accommodationAnterior surface of the lenss becomes more convexPosterior surface of the lens becomes slightly more convexRetinal imageoLight passes through pupil hole and ends up reflected on the retina due to the flipNot all colours are refracted the same oThe image of the actual colour is not exactly in the same spotoImpossible to have perfect refraction oColour vision is blurry but we see details in black and white therefore we are able to seeoTherefore if theres writing really small in a light colour we cannot focus our eyes and therefore is difficult to seeVisual acuity vs contrast sensitivityoTests VAletters become smallerCSletters become lighter until theyre barely thereVA NUMBERATORDEMONINATORoNumeratorviewing distanceoDenominatordistance at which the letter subtends an angle of 5 of arcIn one degree wide one minute of arc 160EmmetropiaoAn emmetropic eye with accommodation relaxed parallel light rays converge to a sharp focused point on the retinaoAt a distance your lens is relaxed and the image is right on the retinaAmetropiaoAny refractive condition other than emmetropiaMyopiarefracts on the retina too earlyNearsightednessEye too longaxial length of the eye longer than normaCorneal curvature too steepfocal length of the optical system shorter than normalOptical correctionsnegative lens spectacle lens or contact lens or refractive surgery change the shape of the corneathe rays converge too much and too soonyou can get closer to objects so that the rays focus on the retina betterat a distance you need the negative lens so that the rays diverge and then converge at the retina
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