VS EXAM 2 REVIEW

In the unaccommodated state, the avg lens pwr is

+20.8 D

How does the distribution pattern for refractive error in a young adult population differ from the theoretical Gaussian (normal) distribution?

- More emmetropes than expected - Less moderate errors - More high refractive errors

_________________ have a positive optical error while ______________ have a negative optical error

- Myopes = Positive optical error (eye too strong), - correction - Hyperopes = Negative optical error (eye too weak), + correction

In a __________________ limited system, you see better as pupil size increases.

Diffraction-limited system (no aberrations) - PSF decreases (better image quality) as pupil size increases

Describe the following for EMSLEY'S reduced eye: a. How many refracting surfaces b. Any refractive error? c. Total power d. r e. Axial length f; Anterior focal length (f) g. n'

a. 1 refracting surface b. No, emmetropic c. Total power = +60 D d. r = 5.55 mm e. Axial length = 22.22 mm f; Anterior focal length (f) = 16.67 mm g. n' = 4/3

Describe the following for Axial Ametropia when corrected at the ANTERIOR focal point: a. RSM (myopes and hyperopes) b. SM (myopes and hyperopes)

a. RSM = 1 for all b. Myopes SM < 1 - Hyperopes SM > 1

Describe the following for Refractive Ametropia when corrected at the Primary Principal Plane (cornea) a. RSM (myopes and hyperopes) b. SM (myopes and hyperopes)

a. RSM = 1 for all b. SM = RSM = 1 for all

Describe what a pt with the following types of astigmatism will see on an astigmatic star a. Simple myopic b. Compound myopic

a. Simple myopic = ONE line will be clear (represents the most + meridian) while all other lines are blurry b. Compound myopic = no lines will be completely clear (b/c no image is formed on retina) but one line will appear darker/clearer than others (this is the power meridian)

List the average values for the lens (mm): a. Thickness b. Anterior radius of curvature c. Posterior radius of curvature

a. Thickness = 3.6 mm b. Anterior radius of curvature = 10.8 mm c. Posterior radius of curvature = -6.5 mm

Lens power decreases abt _________ D every 10 years.

Decreases abt 0.64 D every 10 years

Distribution of Axial length is more peaked than normal which is ______________ and asymmetric (skewed) with a larger number further from the mean w/ _________ axial lengths

- more peaked than "normal" = leptokurtotic - larger number further from the mean w/ LONGER axial lengths

What is the refractive error of a 5D simple myope when viewing an object placed 20 cm in front of the eye?

0 D ~ eye has a +5D error. Obj placed 20 cm in front of eye will have a vergence of -5D at first principal plane which reduces the +5D error to 0.

What is the best pinhole size for clinical use (in mm)?

0.75 - 1 mm

Difference in longitudinal chromatic aberration between 486 and 656 nm is about ___ D

1 D

1 mm change in axial length corresponds to a ____ D change in refractive error

1 mm change = 3 D change in refractive error

Where is the nodal point located in an Emsley reduced eye?

At the CENTER OF CURVATURE (can calculate location by finding "r")

Difference in longitudinal chromatic aberration between 400 and 760 nm is is about _____ D

2.4 D

What is the optimal pupil size?

3 mm (5-8 mm are aberration limited - can't be corrected w/ just specs)

In a __________________ limited system, you see better as pupil size decreases.

Aberration-limited system (normal eye) - PSF increases as pupil size (starts at 3 mm) increases so you see better with smaller pupils (ex: pinholes)

Describe what happens to the following as you push a print closer to your eye: a. Pupil size b. Depth of field

Accn INCREASES so: a. Pupil size decreases b. Depth of field Increases

The ACD reaches adult size at age _________ then at age ______ it DECREASES.

Adult size at age 5-10 Decreases at age 25

Does the following characteristics apply to big or small pupils for a DIFFRACTION-LIMITED EYE (no aberrations) - smaller airy disc - smaller PSF - better image

BIG pupils

How do you determine if the blur circle on the retina will be oriented vertically or horizontally?

Based on which foci is CLOSER to the retina

Place the following from slowest to fastest speed of light: - Red, green, blue

Blue --> green --> red **blue has the highest n

How does increasing light levels help ppl compensate for not being able to accommodate?

Causes pupil size to constrict which increases depth of field

Helmholtz theory of accommodation when viewing a far obj: - the ciliary muscle ________ and the lens _______

Ciliary muscle RELAXES, increases tension in lens zonules and suspensory ligaments which pull on lens to FLATTEN it

Helmholtz theory of accommodation when viewing a NEAR obj: - the ciliary muscle ________ and the lens _______

Ciliary muscle pulls forward to relax tension on zonules which causes lens to THICKEN

Diffraction effects INCREASE as pupil size ___________

Diffraction effects increase as pupils size DECREASES (small pupils are diffraction limited)

T or F: the pushup test (moving near obj closer to test AA) accurately estimates the power change of lens during accn

FALSE - it OVERESTIMATES the power change of the lens during accn

T or F: SM = RSM for axial ametropia corrected

FALSE - only true for REFRACTIVE ametropia

T or F: for refractive ametropias, RSM = 1 when the secondary principal plane of the correcting lens is at the anterior focal point of the eye

FALSE - this is only true for AXIAL ametropias

T or F: in an aberrated eye, the plane wavefront goes into the eye and is perfectly circular

FALSE - this is only true for a diffraction limited (ideal) eye

T or F: All emmetropes have the same axial length

FALSE - you can be emmetropic at ANY axial length as long as the power of eye matches axial length (image forms on retina when fully relaxed)

For high myopes, the probability of estimating their exact prescription by finding their far point DECREASES because...

Far point is at a SHORTER distance which allows for larger variation in refractive error - @ 1 cm, RE = 100 D - @ 2 cm, RE = 50 D

The eye continues to grow after birth and is full-size by age ____

Full size by age 5

Which model of Gullstrand's eye corresponds to the following: - 6 refracting surfaces - Hyperopic (+1 D)

Gullstrand's EXACT schematic eye (#1 eye)

Which model of Gullstrand's eye corresponds to the following: - 3 refracting surfaces - Emmetropic - Refractive index of lens is 1.416 - Pwr of eye directly appropriate for its length

Gullstrand's SIMPLIFIED schematic eye (#2 eye)

Higher order aberrations increase as pupil size __________

Higher order aberrations increase as pupil size INCREASES (big pupils are limited by aberrations)

Place the amt of accommodation for Hyperope, myope, and emmetrope in order from most accn to least accn

Hyper > Emmetrope > myope **hyperopes have to accommodate the MOST

You can INCREASE a ________________ eye's acuity thru minification

Hyperopic eye's

Index of refraction ______ from the surface (cortex) to the center of the lens

INCREASES - index is HIGHEST at the center of the lens

Leading cause of legal blindness is ___________ while leading cause of visual impairment is ________.

Legal blindness = scatter resulting from cataract Visual impairment = uncorrected refractive error

Optics effects of changes in ACD: As the lens moves forward by __ mm, the ACD ______ which increases the eye's total power by ____ D

Lens moves forward by 1 mm --> ACD (t) decreases --> Increases pwr by 1.4 D

You can INCREASE a ___________ eye's acuity by thru magnification from a contact lens correction

MYOPIC EYE'S acuity

For myopes, SM is _______________ because the distance b/w the far point and spectacles is _____________ than the distance b/w the far point to the cornea.

SM < 1 (minification) - Distance from far point and specs is SHORTER than dist. from far point to cornea

For hyperopes, SM is _______________ because the distance b/w the far point and spectacles is _____________ than the distance b/w the far point to the cornea.

SM > 1 (magnification) - Distance from far point and specs is LONGER than dist. from far point to cornea

How does cornea change as we age?

Very stable, doesn't really change unless you get refractive surgery

Describe how each of the following parts of the lens changes as age increases: a. Anterior radius of curvature b. Posterior radius of curvature c. Lens thickness d. Anterior chamber depth

a. Anterior radius of curvature = gets SHORTER b. Posterior radius of curvature = doesn't change c. Lens thickness = thickens at AGE 10 d. Anterior chamber depth = decreases at age 25

Describe whether each structure grows or becomes smaller with age a. Aqueous humor b. Vitreous humor c. Lens

a. Aqueous humor = gets smaller b. Vitreous humor = gets larger c. Lens = gets larger

Describe the distribution pattern of each of these components: a. Corneal power b. Lens power c. Refractive error d. Axial lengths e. ACD

a. Corneal power = Gaussian (normal) b. Lens power = Gaussian (normal) c. Refractive error = Leptokurtic and skewed d. Axial lengths = Leptokurtic and skewed e. ACD = Gaussian (normal) ** All these components can contribute to refractive error but Axial length is the most highly correlated factor

Which type of retinal image quality optical factor limits pupil size and can't be changed? a. Diffraction b. Wave aberration c. Scatter d. Chromatic aberration

a. Diffraction

Describe the 3 general types of eyes in the population: a. Good emmetropes b. Poor emmetropes c. Elongators

a. Good emmetropes = become emmetropic b. Poor emmetropes = maintain their hyperopic features from birth c. Elongators = grow longer and becomes MYOPIC

The CORRECTION of an eye is -5.00 -5.00 x 180. What is the: a. Horizontal ERROR b. Vertical ERROR c. Type of astigmatism

a. Horizontal ERROR = +5.00 @ 180 b. Vertical ERROR = +10.00 @ 090 c. Type of astigmatism = WTR, more powerful in vertical meridian

Describe the following for Refractive Ametropia when corrected at the ANTERIOR focal point: a. RSM (myopes and hyperopes) b. SM (myopes and hyperopes)

a. Hyperopes RSM > 1 - Myopes RSM < 1 b. SM = RSM for refractive ametropia

When you are born you are very ___________ a. Hyperopic b. Myopic

a. Hyperopic (0.5 D around age 1)

Describe the following for Axial Ametropia when corrected at the PRINCIPAL PLANE (cornea) a. RSM (myopes and hyperopes) b. SM (myopes and hyperopes)

a. Myopes RSM > 1 - Hyperopes RSM < 1 b. SM = 1 for all

A pt states that on the astigmatic star the Vertical line is the only clear one. Which of the following could be their prescription? (2) a. Plano -1.00 X 180 b. Plano -1.00 X 090 c. -1.00 +1.00 X 090 d. -1.00 +1.00 X 180

a. Plano -1.00 X 180 c. -1.00 +1.00 X 090 ** when written in + cyl form, clear axis is the cyl axis

Primary, secondary, and tertiary wavefronts are related to a a. bounded system b. unbounded system

a. bounded system **explains how dim light can reach someone eye off axis even if a straight path for rays doesn't make it thru the aperture (pg. 25 week 9)

Correcting a spectacle-wearing HYPEROPE w/ contact lenses or refractive surgery will result in a. minification b. magnification

a. minification

Describe how each of the following are diff. for Refractive =hyperopia compared to Emmetropic eye a. r b. anterior/posterior focal points c. nodal point

a. r gets longer b. anterior/posterior focal points (f and f') move FURTHER away c. Nodal point shifts back towards retina

Describe how each of the following are diff. for Refractive myopia compared to Emmetropic eye a. r b. anterior/posterior focal points c. nodal point

a. radius of curvature gets shorter b. anterior/posterior focal point moves closer to the cornea (f and f' gets shorter) c. nodal point moves forward towards the cornea

At what age range do you lose accn?

age 44-52

What's the power of the cornea for a 4D axial hyperope? a. 64 D b. 60 D c. 56 D

b. 60 D ** for axial hyperopia, power of the cornea is normal - axial length is the cause of refractive errors

Which type of blur would impair reading the most? a. Vertical b. Horizontal c. Oblique

b. Horizontal

As you age and your lens thickens, your correction becomes more a. Myopic b. Hyperopic

b. Hyperopic (more +)

A pt states that on the astigmatic star the Horizontal line is the only clear one. Which of the following could be their prescription? (2) a. Plano -1.00 X 180 b. Plano -1.00 X 090 c. -1.00 +1.00 X 090 d. -1.00 +1.00 X 180

b. Plano -1.00 X 090 d. -1.00 +1.00 X 180

Which type of retinal image quality optical factor deals w/ normal-sized pupils and can be corrected w/ sph and cyl? a. Diffraction b. Wave aberration c. Scatter d. Chromatic aberration

b. Wave aberration

Correcting a spectacle-wearing MYOPE w/ contact lenses or refractive surgery will result in a. minification b. magnification

b. magnification

Which is the preferred method used to correct aphakia? a. spectacles b. contact lens c. IOL

c. IOL then contacts. spectacles is LEAST preferred method b/c will result in a ring scotoma around the edge of the lens

Which type of retinal image quality optical factor is mainly due to the lens and can be fixed with an IOL? a. Diffraction b. Wave aberration c. Scatter d. Chromatic aberration

c. Scatter (lens is major source of scattering)

PSF: a. In a diffraction-limited optical system, as pupil diameter increases PSF diameter decreases b. In an optical system with aberrations, as pupil size increases PSF diameter increases c. a and b

c. a and b

Which type of retinal image quality optical factor occurs b/c all wavelengths don't focus in the same place b/c index of refraction varies for diff. wavelengths? a. Diffraction b. Wave aberration c. Scatter d. Chromatic aberration

d. Chromatic aberration

Which is the standard type of IOL? Pros and cons? a. Anterior chamber IOL b. Iris fixated IOL c. Posterior chamber: ciliary sulcus-fixated IOL d. Posterior chamber: capsule-fixated IOL

d. Posterior chamber: capsule-fixated IOL -Pros: lens is placed inside the capsule -Cons: if capsule opacifies posteriorly, pt has to get a YAG laser capsulotomy

Knowing the PSF of an optical system is important because: a. It can be used to simulate images b. It provides insight to the quality of the optical system c. It allows calculation of the pupil diameter d. a and b e. a and c f. a, b, and c

d. a and b

Very small pupil diameters: a. Act as a spatial filter - the smaller the pupil the greater the loss of spatial information b. Impact higher spatial frequencies more than very low spatial frequencies c. Decrease the amount of light passing through d. a and b e. a and c f. a, b and c

e. a and c - Act as spatial filter - Decrease amt. of light passing thru

Airy disk: a. Formed in the image plane of an in-focus near-perfect optical system b. Is dependent on wavelength and pupil size c. Is the image of an on-axis object point d. a and b e. a, b and c

e. a, b and c

Punctum remotum is referring to the _____________ of the eye

far point of the eye

Rayleigh resolution limit improves in a near aberration free system more for _______ wavelengths

improves more for SHORT wavelengths than long ones

As age increase, what happens to equivalent index of refraction (neq)?

neq DECREASES

Does the following characteristics apply to big or small pupils for a DIFFRACTION-LIMITED EYE (no aberrations) - big airy disc - big PSF - poor image

smaller pupils

TOTAL RMS wavefront error is equivalent to

the standard deviation of the wavefront error over the pupil