Optics instrumensOptics instrumensEyeEyeLupLupMicroscoopeMicroscoopeTeropongTeropong

The Eye – Close-up of the The Eye – Close-up of the CorneaCornea

The EyeThe Eye

The normal eye focuses The normal eye focuses light and produces a sharp light and produces a sharp imageimage

Essential parts of the eye:Essential parts of the eye: Cornea – light passes Cornea – light passes

through this transparent through this transparent structurestructure

Aqueous Humor – clear Aqueous Humor – clear liquid behind the cornealiquid behind the cornea

The Eye – Parts, cont.The Eye – Parts, cont.

The pupilThe pupil A variable aperture A variable aperture An opening in the irisAn opening in the iris

The crystalline lensThe crystalline lens Most of the refraction Most of the refraction

takes place at the takes place at the outer surface of the outer surface of the eyeeye Where the cornea is Where the cornea is

covered with a film of covered with a film of tearstears

An intuitive way to view eye An intuitive way to view eye correctionscorrections

Near-sighted eye is elongated, image of distant object forms in front of retina

Add diverging lens, image forms on retina

Far-sighted eye is short, image of close object forms behind retina

Add converging lens, image forms on retina

The Eye – Near and Far PointsThe Eye – Near and Far Points

The The near pointnear point is the closest distance for which is the closest distance for which the lens can accommodate to focus light on the the lens can accommodate to focus light on the retinaretina Typically at age 10, this is about 18 cmTypically at age 10, this is about 18 cm The average value is about The average value is about 25 cm25 cm It increases with ageIt increases with age

Up to 50 cm or greater at age 60Up to 50 cm or greater at age 60

The The far pointfar point of the eye represents the largest of the eye represents the largest distance for which the lens of the relaxed eye distance for which the lens of the relaxed eye can focus light on the retinacan focus light on the retina Normal vision has a far point of infinityNormal vision has a far point of infinity

NearsightednessNearsightedness(Myopi)= Rabu jauh(Myopi)= Rabu jauh

Also called Also called myopiamyopia The far point of the nearsighted person is not infinity The far point of the nearsighted person is not infinity

and may be less than one meterand may be less than one meter The nearsighted person can focus on nearby objects The nearsighted person can focus on nearby objects

but not those far awaybut not those far away

Correcting NearsightednessCorrecting Nearsightedness

A diverging lens can be used to correct the A diverging lens can be used to correct the conditioncondition

The lens refracts the rays away from the The lens refracts the rays away from the principal axis before they enter the eyeprincipal axis before they enter the eye This allows the rays to focus on the retinaThis allows the rays to focus on the retina

Eyeglasses with concave lenses used Eyeglasses with concave lenses used overcome nearsightedness must have overcome nearsightedness must have lens strength (P) = kekuatan lensa :lens strength (P) = kekuatan lensa :

Pr

100P

Pr = Punctum Remotum of eye ( cm)

= titik jauh mata

FarsightednessFarsightedness( rabun dekat/ hypermetropia)( rabun dekat/ hypermetropia)

Also called Also called hypermetropiahypermetropia The near point of the farsighted person is muchThe near point of the farsighted person is much farther farther away than that of the normal eye away than that of the normal eye The image focuses The image focuses behindbehind the retina the retina Can usually see far away objects clearly, but not nearby objectsCan usually see far away objects clearly, but not nearby objects

Correcting FarsightednessCorrecting Farsightedness

A converging lens placed in front of the eye can A converging lens placed in front of the eye can correct the conditioncorrect the condition

The lens refracts the incoming rays more toward the The lens refracts the incoming rays more toward the principal axis before entering the eyeprincipal axis before entering the eye This allows the rays to converge and focus on the retinaThis allows the rays to converge and focus on the retina

Farsightedness eyes Farsightedness eyes have the Punctum have the Punctum Proximum greater than Proximum greater than 25 cm and the punctum 25 cm and the punctum remotum at unlimited.remotum at unlimited.

Eye glasses with Eye glasses with convex lenses used to convex lenses used to overcome overcome Farsightedness must Farsightedness must have the lens strength :have the lens strength :

PpP

100

Pp = Punctum Proximum = titik dekat

PpP

1004

Presbyopia and AstigmatismPresbyopia and Astigmatism

PresbyopiaPresbyopia (literally, “old-age vision”) is due to (literally, “old-age vision”) is due to a reduction in accommodation abilitya reduction in accommodation ability The cornea and lens do not have sufficient focusing power The cornea and lens do not have sufficient focusing power

to bring nearby objects into focus on the retinato bring nearby objects into focus on the retina Condition can be corrected with converging lensesCondition can be corrected with converging lenses

In In astigmatismastigmatism, light from a point source , light from a point source produces a line image on the retinaproduces a line image on the retina Produced when either the cornea or the lens or both are Produced when either the cornea or the lens or both are

not perfectly symmetricnot perfectly symmetric Can be corrected with lenses with different curvatures in Can be corrected with lenses with different curvatures in

two mutually perpendicular directionstwo mutually perpendicular directions

DioptersDiopters

Optometrists and ophthalmologists usually Optometrists and ophthalmologists usually prescribe lenses measured in prescribe lenses measured in dioptersdioptersThe power The power PP of a lens in diopters equals the of a lens in diopters equals the

inverse of the focal length in metersinverse of the focal length in metersPP = 1/ƒ = 1/ƒ

Student ActivityStudent Activity

Anton’s retina is Anton’s retina is 2.5 cm2.5 cm behind the lens, which has a behind the lens, which has a minimum focal length of minimum focal length of 2.6 cm2.6 cm..

1. What does the focal length 1. What does the focal length ffclcl of her contact lens of her contact lens

need to be?need to be?

(a) 65 cm (c) -0.1 cm(b) -65 cm

2. What is the power Pcl of the contact lens?

(a) 1.5 D (c) 1000 D(b) -1.5 D

2.5 cm

feye = 2.6 cm

Compound MicroscopeCompound Microscope

A compound A compound microscope consists of microscope consists of two lensestwo lenses Gives greater Gives greater

magnification than a magnification than a single lenssingle lens

The objective lens has a The objective lens has a short focal length, short focal length,

ƒƒoo< 1 cm< 1 cm The eyepiece has a The eyepiece has a

focal length, ƒfocal length, ƒee of a few of a few cmcm