Visual Optics Exam 1: Ch 4-7

What are the three classification systems for astigmatism?

-classification by regularity -classification by focal line location -classification by axis of astigmatism

List the 5 types of classification by focal line location for astigmatism

-compound myopic astigmatism -simple myopic astigmatism -compound hyperopic astigmatism -simple hyperopic astigmatism -mixed astigmatism

Describe the 3 type of chromatic aberrations

-longitudinal chromatic aberration (LCA): shorter wavelengths image more anteriorly in eye than long wavelengths -transverse chromatic aberration (TCA): displacement of pupil can cause mis-location (sideways) of light rays of different colors. -chromatic difference of magnification (CDM): large, extended object perceived to have rainbow edge with blue toward middle and red toward edge.

Describe the two types of classification by regularity for astigmatism

-regular astigmatism: eye power is maximal and minimal at two meridians separated by 90 degrees -irregular astigmatism: meridians of maximal and minimal power are not separated by 90 degrees and/or eye cannot be corrected by spherocylindrical lens. due to particular monochromatic aberrations

Give an example of optical property of the pupil that affects vision in daily life

-retinal illuminance -depth of field (focus) -optical quality due to aberrations and/or diffractions

List the 7 sources of retinal image blur

-spherical defocus -astigmatic defocus -chromatic aberrations -monochromatic aberrations -diffraction -intraocular scatter -motion blur

How could you make the Emsley eye accommodate since it doesn't have a crystalline lens?

decrease the radius of curvature (r) to increase power

What is hyperopia also known as?

hypermetropia

Describe target distance effects on paraxial image location

if RO moves toward the eye, image moves posteriorly in the eye. If RO moves away from the eye, the image moves anteriorly in the eye

What is an optical role for the sclera of the eye?

provides support for the retina and keeps vitreous chamber depth stable (hence keeps refractive error stable)

What is one advantage of the Emsley eye?

simple calculations

Describe paraxial eye

spherical refracting surfaces and these surfaces centered on a common optical axis. Three types

Given +1.00 -0.50 x 180, carry out calculations involving refractive errors with Thibos et al dioptric power vector

P = [0.75 +0.25. 0]

Describe Thibos et al diptric power vector

P = [M J0 J45], where M is mean spherical equivalent/best sphere, J0 is power of JCC with axis 180 degrees, and J45 is power of JCC with axis 45 degrees. To convert to vector format: M = S + (C/2) J0 = -(C/2)cos2α, J45 = -(C/2)sin2α

What is a point spread function?

PSF is a two-dimensional intensity distribution of a point source at the retinal plane

What is a cataract?

loss of transparency of the crystalline lens

Katherine has an ocular refraction of −2.00 DS in her right eye and +1.00 DS in her left eye. (A) Which eye receives the clearest image when she views a distant object with relaxed accommodation? (B) Which eye receives the clearest image when she views an object at a distance of 1 m with relaxed accommodation? Please include number-line diagrams of each case.

(A) The left eye would receive the clearest image because it is closest to the retina (B)1 m is 1 D of accommodation. Both images would move posteriorly 1 D. The right eye would receive the clearest image

(A) Now show what happens if Kurt were to wear his old spectacle lens of power −2.50 DS while viewing a book at a distance of 40 cm. (B) Then, determine which level of accommodation will place the circle of least confusion at the retina.

(A)The -2.50DS will move the astigmatic interval posterior 2.50D. The book distance of 40 cm will also move the astigmatic interval posterior 2.50D, for a total movement of 5D. There will be a posterior focal line at 2.00D oriented 120 degrees and a posterior focal line at 1.25D oriented 30 degrees. (B)The CLC is calculated from the mean spherical equivalent M to be 1.625D. Kurt will need to accommodate by +1.625D for the CLC to fall on the retina.

What is the paraxial pupil ray angle ratio?

(m) a ray directed toward the center of the entrance pupil appears to emerge from the center of the exit pupil, this ray is the chief ray or paraxial pupil ray. u is the angle of incidence and u' is the angle of the refracted chief ray, then m = u'/u

Describe an Emsley's reduced eye

--+5.5mm radius of curvature of its single refractive surface; --refractive index medium is 1 1/3; dioptric power of +60D; --second principal focal length: +22.22mm --Eye is entropic with one refracting surface and axial length corresponds to its second principal focal length (f') --Principal points lie at the refracting surface and nodal points lie at the center of curvature of the refracting surface. --There is no aperture stop and retina is a plane but typically is drawn curved for models

Describe how fick's axes differ from OSA axes

--Horizontal plane: X for both --Vertical plane: Z for Ficks and Y for OSA --Anterior-posterior sagittal plane: Y for Ficks and Z for OSA --Center: at center of rotation for Ficks and center of entrance pupil for OSA

Based on your current knowledge as a first-year student, which sources of blur can be corrected by optometrists? Which sources cannot currently be corrected?

--Spherical and astigmatic defocus: corrected with spectacles and/or contacts --Monochromatic aberrations: prevented from being too high through wavefront LASIX --Scatter: from cataracts reduced by cataract removal and intraocular lens implantation *Chromatic aberrations and diffraction: aren't correctable by optometrists

Give an example of the statement: "schematic eyes deemphasize individual variability in ocular components."

--corneal curvature varies between people but Gullstrand No 1 eye has a fixed anterior corneal radius of curvature --Emsley eye has a fixed axial length, but real people's eyes axial lengths differ and this variation between people important factor in refractive error

Describe focal points

--first principal focal points (F) is the point on the axis at which an object must be placed to provide an image at optical infinity --Second principal focal point (F') is the point on the axis which an image is formed from an object at optical infinity

What are the two types of component ametropia?

-axial ametropia: occurs when axial length is abnormal -refractive ametropia: occurs when one or more of the refractive components is abnormal

Describe the three classification by axis of astigmatism

-with the rule astigmatism: meridian of highest positive ocular power is closer to the vertical (90 +/- 30 degrees). eye corrected with negative cyl device that has axis in 180 +/-30. -Against the rule astigmatism: meridian of highest positive ocular power is closer to the horizontal (180 +/- 30 degrees). Eye corrected with negative cyl device that has axis in range of 90 +/-30. -oblique: axis of correcting cylinder is neither with the rule or against the rule

Describe the three paraxial construction methods for images of extended objects

1. classical lateral magnification: estimates image height through principal points, equivalent power, and lens formula. L is object mergence, L' is image mergence, lateral mag is m=L/L' and h'=mh. Cannot be used with L or L' =0 2. Nodal points method: trace a ray from object point to N and then from N' to intersection with retina (this is nodal ray). Based on fact that incident ray directed toward N emerges from N' at SAME angle. Not valid method if retinal image is defocused. 3. Entrance and exit pupil method: chief ray traced from an object point to the center of the entrance pupil and then from center of the exit pupil to its intersection with the retina, using m=u'/u (m is paraxial pupil ray angle not lateral magnification)

How does the special property of nodal points differ from the entrance and exit pupil special imaging property?

A ray directed toward center of the entrance pupil appears to emerge from the center of the exit pupil. U is the angle of indent chief ray and u' is the angle of refracted chief ray but these angles are not the same. The incident ray directed toward the nodal point N and emerging from the second nodal point N' are the SAME angle from the optical axis.

Kurt has an ocular refraction of −3.00 / −0.75 × 030. Please draw a number-line diagram of his eye showing the location of the astigmatic interval and circle of least confusion when viewing a distant point object with relaxed accommodation

Anterior focal line at 3.00D oriented at 120 degrees, anterior focal line at 3.75D oriented 30 degrees, and CLC at 3.375D.

What distinguishes axial ametropia from refractive ametropia?

Both are type of component ametropia in which a component falls outside the range for emmetropes but axial ametropia refers to an abnormal axial length while refractive ametropia refers to one or more refractive components being abnormal.

Stacy has uncorrected myopia. She views a distant object with relaxed accommodation. How can she improve the clarity of her vision without lenses or surgery or orthokeratology, at least temporarily? Show why this works in two ways: (a) using side-by- side optical diagrams; and (b) by way of Smith's equation.

By reducing her pupil size, she can reduce the blur circle on her retina and improve the clarity of a distant object by: Pinholing: place pinhole in front of pupil to reduce pupil size Bright light: go outside into bright light and pupil will reduce in size (b) Φ = d∆L; ∆L represents amount of defocus (D) which is kept constant as image location stays the same; the size of pupil d is directly proportional to the angular size of the blur circle Φ. Therefore, decreasing the pupil size d through pinholing or addition of a bright light will decrease blur circle.

Tim's right eye has 1 D of with-the-rule corneal astigmatism by keratometry. By Javal's rule, what total eye astigmatism do you expect? Please show your working.

CT = 1.25CC -0.5 = 1.25(1.00) -0.5 CT = 0.75D

In an emmetropic eye, light from a distant object focuses at the plane of the retina. This indicates that the ____________ in such an eye lies at the retina

F' (second principal point)

Draw two reduced eyes in exaggerated form to show how two eyes with different powers and axial lengths could both still be emmetropic.

First eye will have steeper surface (more power) with a shorter axial length. Second eye will have flatter surface (less power) with longer axial length. Key for them both to be emmetropic still is the balance between axial length and eye power.

Describe JJ Gibson's optic array

Gibson theorized how visual perception is understood based on surrounding environment through use of optic arrays. The optic array is a set of solid angles that surround any point in air in the real world. These solid angles correspond to large and small objects. Solid angles are nested and the array must have structure provided by light reflected from various surfaces in the environment that surround the point.

Explain the principal of the Hirschberg test

Hirschberg test provides an object gross assessment of eye alignment, particularly for infants. The subject fixates on a small source, such as a penlight. Light is reflected from the anterior corneal surface and is visible to the examiner as a small image, a Purkinje-Sanson (PS) image. In binocular viewing, both images normal sit slightly nasally in their respective pupils. However, in strabismus one eye does not fixate the target with its anatomical fovea during binocular viewing. This may be observed as displacement of one PS image within the pupil from its normal location.

Draw a diagram of a model eye with first and second nodal points and describe the important practical property of light rays and nodal points.

Incident ray directed toward first nodal point N appears to emerge from second nodal point N' and at the same angle from the optical axis as the incident ray.

If you were to shorten the axial length of the Emsley eye by 2 mm, what would be its new ocular refraction (K)? State first of all what you would expect intuitively, then use equations to find an exact answer. Please show your working

Intuitively, shortening the axial length should cause the eye to become hyperopic as the image will now focus posterior to the retina instead of on the retina. Eye's power is now too low for its axial length and therefore power should increase. Emsley eye: 22.22mm and 60D with index 1.333 K' = 1/k = 1.333/0.02022m = +65.94D K = K' -De = 65.94D - 60D = +5.94D

What is a diffraction limited point spread function?

PSF obtained when diffraction is the only remaining factor that limits/degrades the retinal image

What is Javal's rule?

Javal's rule represents that rough relationship between corneal astigmatism (Cc), presumed lenticular astigmatism, total astigmatism (Ct) ,represented by Ct = 1.25Cc -0.5 + indicates with the rule - indicates against the rule doesn't apply to obliques

Jarred cannot see distant objects very clearly. He can see things sharply at 22 cm in front of his eye with relaxed accommodation. What might his ocular refraction be? Is he myopic or hyperopic?

K = 1/k ; K = 1/-0.22m = -4.54D, he is myopic

Augustine has an ocular refraction of +2.00DS. Where is his far point located? include a diagram

K = 1/k = +2.00DS = 1/k....k=+0.5m posterior to the first principal point

Kimberlee has an ocular refraction of -1.25DS. Where is her far point located? Include a diagram

K = 1/k = -1.25DS =1/k... k =-0.8m anterior to the first principal point

Kelsey has a virtual far point. It is located 14 cm posterior to her first principal point. What is her ocular refraction? Show with a diagram the principle of the far point using Kelsey's eye as an example.

K = 1/k, K =1/+0.14m = +7.14D

Kent is reading a book at a distance of 30 cm. His accommodation is perfect. He sees the words very clearly. If he now glances to his phone at a distance of 17 cm, how many diopters of accommodation must he add to see his phone perfectly clear?

Kent will need 2.55D of accommodation

An emmetropic reduced eye view an object at a distance of 3m with relaxed accommodation. The eye has a power to +65D and the refractive index of its medium is 1.336. What is the image distance?

L' = D +L n'/x' =D + n/x 1.336/x' = +65D +1/-3m x' =20.66m

Joanna has an ocular refraction of −4.00 / −1.00 × 90. (A) What sphere lens will place the circle of least confusion at the retina? (B) Put this lens in place and show the astigmatic interval in her eye. (C) Show by the diagram the effect of adding −1.00 DC × 90. (D) Remove that cylindrical lens and then show the effect of adding −1.00 DC × 180.

M = S + (C/2) = -4.00 + (-1.00/2) = -4.50DS Addition of -4.50DS pushes interval posterior by 4.50D, placing CLC on retina Add of -1.00DCx 090 will only move axis 90 (orange in pic) posterior 1.00D and will move it to 0.50 posterior to the retina, on the same position as the horizontal axis. This will collapse the interval to a point focus at 0.50D posterior. Add of -1.0 0DC x 180 will only move axis 180 (purple in pic) posterior 1.00D and will move it to 1.50 posterior to retina. The CLC will be 0.50 posterior to retina and axis 90 will stay at 0.50 anterior to retina.

Describe the meaning of the three members of the vector P in as simple language as you can.

M is mean spherical equivalent (a sphere lens) J0 is JCC with its axis located at 180 degrees J45 is JCC with its axis at 45 degrees

Dion is emmetropic, presbyopic and has no remaining accommodative ability. He wishes to read the newspaper at a distance of 30 cm but has great difficulty. What is your first estimate of the power of the required reading addition lens? Include magnitude (diopters) and sign. Indicate how you arrived at this conclusion, from first principles.

Reading a newspaper at 30cm means his image point will be 3.33D behind the retina. He will need a plus powered lens to move his image anteriorly, specifically a +3.25 or +3.50DS would fall within the 3.33D range

You perform a subjective refraction in Desiree's right eye. She is myopic by 2 D, presbyopic (cannot accommodate), and views the distant wall chart. With −1.75 DS in the trial frame, you ask her 'which appears sharper, one or two?', as you place loose sphere lenses of +1 DS then −1 DS in front of lenses already in the trial frame. Which will she prefer, and why?

She will prefer the -1.00DS lens. The +1.00DS lens yields a final image 1.25D in front of the retina while the -1.00DS yields a final image 0.75D behind the retina. The patient will prefer a lens that produces the closest image to the retina and therefore -1.00DS.

Your quest is to create a new reduced eye for studies of experimental myopia in the domestic chick (Gallus gallus). Based on available data for the 7-day old chick, you wish to have an eye with an equivalent power of +176.5 D. For convenience, the eye is filled with water (n′ = 1.333). The eye is emmetropic; that is, light from a distant object is focused at the retina. Determine the necessary surface radius of curvature and axial length. Show your working, and draw your final eye.

Since light from a distant object focuses at the retina, you can then equate axial length with f'

Describe the features of the Smith equation

Smith equation tells the angle of an object's blur disc based on the size of the eye pupil and amount of defocus of the image location from the retina on the eye. The blur circle increase with larger defocus and with larger pupil diameters. Φ = d∆L, where d is entrance pupil diameter (m) and ∆L is amount of defocus (D) and answer Φ is in radians. Will give perceived angular size of the blur disc in object space radian to degrees: rad x 180/π

What is the blind spot? Why do you have one?

The blind spot corresponds to the optic nerve head, which has no photoreceptors there, 15 degrees temporal to fixation point in object space.

Draw a diagram to show the appearance of a Punkinje-Sanson image in the case of left exotropia

The left eye should turn out and the right eye should fixate. The left eye PS image would be closer to the nasal side of the pupil but he eye should be turned out. Right eye will have PS image in the center of the pupil.

Explain how the upper limit of visual resolution is based in part on cone receptor sampling.

The mean inter-cone spacing defines one upper limit on the resolution performance of the eye. A single cone is projected into object space using a simple model of the eye's optics. The resolution is obtained when one photoreceptor corresponds to the limb of the Snellen letter and one to the gap between limbs. So to be able to resolve must have at least one cone for each limb of letter and each gap.

Describe ocular refraction (K) in regards to myopia and hyperopia

The refractive state of an eye may be specified by its ocular refraction. The ocular refraction (K) is the reciprocal of the far point distance (k); K = 1/k ... in diopters In myopia, K is negative In hyperopia, K is positive In emmetropia, K is zero

Why might is be difficult or impossible to see very small, dim objects when fixating them directly at night?

There are no rods in the very center of the fovea when trying to fixate and in dark conditions, using primarily rods.

Give an example of a schematic eye that ignores one or more genuine components of the real eye

a reduced eye has no crystalline lens

Charles is emmetropic. He reads a book at a distance of 25cm. (a) how much accommodation must he exert to see the text clearly? (b) if he now wears +1.50DS reading spectacle, how much accommodation must he exert?

a. 25cm = 4D accommodation; the book moves toward the eye which pushes image posteriorly 4D b. 2.50 accommodation (4D-1.50D =2.50D); positive lens moves the image anteriorly toward the retina

What is one advantage of the Gullstrand-Emsley eye?

ability to accommodate

Describe the Helmholtz model for accommodation

accommodation for a near object is achieved through the following steps: 1. The ciliary muscle inside ciliary body contracts and moves toward middle 2. This relaxes tension of the zonules, allowing the crystalline lens to adopt a more curved shape (diameter of lens and ROC for both surfaces decrease) as lens thickness increases and moves toward anterior chamber 3. Lens has more positive power and causes image of the near object to focus closer inside the eye

What is the function of the crystalline lens?

accommodation: deformable structure to adopt different positive powers

What is the function of the iris?

acts as an aperture stop of the eye and can alter retinal illuminance

What is a nodal point in relation to schematic eye

allow for simple image size calculations; an incident ray direct toward first nodal point N appears to emerge from the second nodal point N' and at the same angle from the optical axis as the incident ray

Define angle alpha, draw a diagram, and show how it depends on two axes. Label those axes.

angle between optical axis and visual axis. Measured in practice as angle between optical axis and line of sight

Define angle lambda

angle between pupillary axis and the line of sight (aka angle Kappa)

What is the function of the tear film?

anterior surface performs initial refraction of light but tear film contributes to virtually zero power; quality of tear film affects visual performance

Korey is myopic. With relaxed accommodation, he sees an object clearly when it is placed at a distance of 33cm from his eye. Assuming no change in accommodation, a distance object is imaged where? Korey now wishes to see the mountain ranges clearly. What is your first guess at the required correcting lens to allow Korey to see the mountains? Explain your logic.

anterior to the retina by 3D. Korey needs a -3.00DS lens to see clearly. Based on the drawing in the previous question, Korey's image falls anterior to the retina before correction. Thus a negative lens will push the image back onto the retina.

Describe a finite (wide angle) eye

aspheric, any eye that does not meet criteria to be paraxial

What is compound myopic astigmatism?

both focal line myopic

What is compound hyperopic astigmatism?

both focal lines are hyperopic

What is the aperture stop?

component which alone determines the amount of light that reaches the image from an on-axis point source

What is correlation ametropia?

components are within the usual range for emmetropes, but components do not balance correctly; can't be traced to axial length or ocular power b/c all parameters are within normal ranges for emmetropes. Considers only the component of one eye at a time

Define visual axis

composed of two line segments: the first connects the fixation point to the first nodal point (N) and the second connects the second nodal point (N') to the fovea

How do cone and rod densities vary across the retina?

cone density at maximal at the fovea, whereas rod density at about 20 degrees eccentricity. No rods in the central 1 degree of the retina

Describe principal points in relation to schematic eye

conjugate points that allow schematic eye to be treated as a thin lens. When P is known, can measure object distance from P, calculate x' using L' =De +L and then measure distance from P'

Give an example of how the wide variability in corneal radius of curvature between individuals is of relevance to optometric practices

contact lens fittings

What is the function of the cornea?

contributes to 2/3 of the total refracting power of the eye with tear film; important for transparency

What is the convolution process, as applied to imaging in the eye? Describe convolution with a digital image as the starting point.

convolution is a mathematical procedure used to estimate the appearance of the image of an extended object based on known point spread function (PSF). In practice, distant object points are projected to the retina but instead of as image points, replaced with PSF to obtain the retinal image. Convolution estimates the appearance of the image of an extended object based on known PSF. With a digital image, each pixel in the image is treated as a point and is replaced by a PSF.

What are the contribution of the cornea and lens to ocular power?

cornea: +42D lens: +19D for distance (+30 for near ~10cm)

The cornea contributes to about _______ of eye's dioptric power while crystalline lens contributes to ________ of eye's power

cornea: 2/3 lens: 1/3

Give an example of intraocular scatter

crystalline lens or cataracts of the lens in aging individual

Give an example of a task that is difficult for uncorrected myopes, and indicate why this is so based on visual optics

distant objects will appear blurred, as the far point of the myopic eye is located in real space somewhere closer than infinity

Describe with a picture the difference between crystalline lens equatorial diameter and lens thickness

equatorial diameter: diameter of lens at equator (left to right width of lens @ widest point) lens thickness: for-aft dimension from front to back of lens

Describe ocular power effects on paraxial image location

eye's power increases, the image move anteriorly in the eye, if the ocular power decreases, the image moves posteriorly in the eye.

What is the function of the aqueous humor?

fill anterior and posterior chambers; maintains the intraocular pressure of the eye

What is the function of the vitreous humor?

fill eye and vitreous chamber depth is best predictor of individual refractive error

Describe target vergence effects on paraxial image location

if wavefront mergence is made more negative (more divergent or less convergent), the image moves posteriorly in the eye. If the wavefront is made more positive (less divergent or more convergent) the image moves anteriorly in the eye.

Give an example of motion blur

image moves too quickly across the retina and a perceptual smearing results

What is the entrance pupil?

image of the aperture stop formed by optical components anterior to the aperture stop when viewed from object space

Describe a reduced eye model of the sources of refractive error

in a reduced eye model, ocular refraction K depends on the balance between equivalent power of the eye (De) and equivalent dioptric length (K'). Ametropia results if eye is too short or too long for its dioptric power

What is the first Punkinje-Sanson image? How is it formed?

it is a reflection from the anterior corneal surface

What is the Stiles-Crawford effect? What is one possible benefit for this effect?

light entering the eye from the edge of the pupil is less effectively transduced than light from the center of the pupil. Benefit: reduces glare from extra ocular light scatter; hypothesized to reduce deleterious effects of ocular aberrations, resulting in slightly better visual acuity and contrast sensitivity

Describe an unaccommodated myopic eye

light from distant object imaged anterior to the fovea; eye's power too great for its axial length; refractive prescription is a negative spherical lens

Describe an unaccommodated emmetrope

light from distant object imaged at the fovea; refractive prescription is plano powered lens

Describe an unaccommodated hyperopic eye

light from distant object imaged posterior to the fovea; eye's power is too low for its axial length; refractive prescription is a positive spherical lens

Give an example of astigmatic defocus

light in one meridian refracted more strongly than that in the meridian 90 degrees away

Give examples of the effects of refractive error in daily life

light night imaging on fovea so blurred vision results for near or far objects for myopic and hyperopic eye. Astigmatic eye will either see horizontal or vertical components at different blurs until corrected

Give an example of diffraction

light rays that pass through a small pupil form patterns of construct and destructive interference at the retinal plane

Define pupillary axis and draw a diagram

line normal to anterior corneal surface (containing the center of curvature of the anterior corneal surface Cc) that pass through the center of the entrance pupil.

Define optical axis

line of best fit through centers of curvatures of all surfaces since no true optical axis in eye exists due to decentration, tilts, and asphericities of various surfaces

Why is it advantageous to have accommodation in daily life?

mainly to observe sharp images of near objects

Give an example of spherical defocus

myopia and hyperopia

What are the practical consequences of the far point location in the myopic eye?

objected placed at the far point don't require accommodative effort. This is useful for presbyopic myopes. Objects closer than the far point require accommodative effort.

What is component ametropia?

one (or more) components fall outside the usual range for ememtropes.

What is simple myopic astigmatism?

one focal line formed at retina, other is myopic

What is simple hyperopic astigmatism?

one focal line is formed at the retina, other is hyperopic

What is mixed astigmatism?

one focal line myopic and other is hyperopic

What are the two types of schematic eyes?

paraxial and finite

Define line of sight and draw a picture

path of chief rays from fixation point to center of the entrance pupil. This line describes the center of the actual pencil of rays that enters the eye.

Describe an astigmatic eye

power of the eye changes with each meridian. Refractive prescription has cylinder component

Describe the three types of paraxial eyes

reduced eye: one refracting surface and its single refractive medium has uniform refractive index. Ex: emsley eye Simplified eye: single corneal surface and a crystalline lens with two surfaces and uniform refractive index Exact eye: eye has at least two corneal surfaces and at least two crystalline lens surfaces. ex: Gullstrand No 1 eye

Repeat the prior question using the entrance-exit pupil construction method. Assume that the entrance pupil and the exit pupil are at the vertex of the single refracting surface, and that the paraxial pupil ray angle ratio is 0.75.

retinal image height: 1.25mm (* use trig to solve for u, then find u' using paraxial. pupil ray angle ratio)

The Emsley eye views a person 1.5 m tall who is standing 20 m away. Use the nodal point construction method to calculate the retinal image height. (The two nodal points in the Emsley Eye are on top of each other and are 5.55 mm posterior to the single refracting surface.)

retinal image height: 1.25mm (*use trig to solve for first angle and remember that in nodal point construction method, the two angles are equivalent)

Which photoreceptors operate in scotopic conditions (darker) and which operate in photopic (lighter) conditions

scotopic: rods photopic: cones mesopic region: dim; both photoreceptors operate

Give an example of monochromatic aberrations

seidel and zernike systems

Give an example of how accommodation may be useful to a young hyperope

the far point of hyperope is virtual object point located somewhere behind the corneal vertex. All objects are blurred without accommodative effort and both distant and near objects will require accommodative effort to be seen clearly.

What optical functions are modeled by the four-surface nature of the crystalline lens in the Gullstrand No. 1 eye?

the four surfaces attempt to model the gradient index of the real crystalline lens

What is presbyopia? How might presbyopia influence your daily activities as you grow older?

universal age related loss of accommodative amplitude. As amplitude decreases, lose ability to focus on and read near objects

Which part of the eye causes the Stiles-crawford effect?

the photoreceptors of the retina

What is anisometropia?

the two eyes have unequal refractive error, either myopic, hyperopic, or antimetropia (one myopic, other hyperopic)

To which ocular axis does the z-axis of the OSA standard reference frame correspond?

the z axis corresponds to the line of sight; it is the path of the chief ray from fixation point to the center of the entrance pupil

Beau has a refraction of +0.50 DS without cycloplegia. With cycloplegia (1 drop of 0.5% cyclopentolate), he has a refraction of +2.00 DS. What are the values of his total, manifest, and latent hyperopia?

total = cycloplegic refraction: +2.00DS manifest = dry non-cycloplegic: +0.50DS total = manifest + latent +2.00DS = +0.50 + latent; latent = +1.50DS

Describe the components of hyperopia. How else can hyperopia be measured?

total = manifest + latent, where total represents the cycloplegia refraction, manifest presents the dry, noncycloplegic measurement, and latent is the portion hidden by a person accommodating that must be calculated based on total and manifest also measured by components of total = facultative + absolute, where if person is exerting max accommodation from the facultative component, determines how much hyperopia can be hidden

What is the function of the retina?

transduces light to photoreceptors

What is a possible consequence for tear film breakup for vision?

visual performance declines. For example, contrast sensitivity is reduced when a person voluntarily stops blinking

What is the most significant predictor of spherical ametropia?

vitreous chamber depth is best predictor of ocular refraction in all refractive error groups

Melissa has a spectacle prescription of RE +0.25DS -0.75DC x 012. Does she have with the rule, against the rule, or oblique astigmatism

with the rule

Regina has a prescription of -6.50DS -0.50DC x 170 for the left eye in her glasses. Does she have with the rule, against the rule, or oblique astigmatism?

with the rule

What is with the rule astigmatism?

with the rule astigmatism is when the meridian of greatest focal power is closer to the vertical of 90 degrees +/- 30 degrees. The refractive surface of the eye may be though of as a football lying flat. The eye is corrected with negative cylinder with its axis in the range of 180 degrees +/- 30 degrees.

An eye with 5 D of defocus views a point object. The eye's entrance pupil is 3.5 mm in diameter. What is the angular diameter of the perceived blur circle (min arc) by Smith's geometrical optical approximation?

Φ = d∆L, where ∆L=5D and d=3.5mm=0.0035m Φ = (5d)(0.0035m) = 0.0175 rad (x 180/ π = 1.003 degrees)