The visual perception of an image depends on:
a) the spectral distribution of light falling on the object
b) the anatomy and physiology of the eye
c) processing in the visual cortex
d) all of the above
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An object is placed 6 cm in air (n=1) to the left of a thin lens (n'=1.500). The radius of curvature of the front and the back surfaces of the lens are r1 = 5.5mm and r2 = -4mm respectively. Where will the image be? Would it be virtual or real, and magnified or minified?
Hint: calculate the power of the front and back surfaces (n'-n/r). Then calculate the total power of the thin lens. Finally, calculate the image vergence L' L+F, and convert it into cm.
Which of the following is true about UV radiation? a) UV radiation of about 1400 nm reaches the retina b) The majority of UV radiation is absorbed by the cornea and the lens c) UV radiation of about 400 to 700 nm is absorbed by the lens d) Exposure to UV radiation could cause retinal burns and cataractbWhich one of these sentences about the anterior corneal surface is false? a) Most refraction of the eye occurs here due to the significant change in refractive index between the air and the anterior cornea b) Reflection is greater than that from the other three reflecting surfaces of the eye c) Refraction at the anterior corneal surface is higher than at the posterior corneal surface. d) It causes minimum refraction due to the significant change in refractive index between air and the anterior corneadWhich of the following is true about angle alpha? a) It is the angle between the visual axis and the pupillary axis b) It is negative if the visual axis is to the nasal side of the optic axis in the object space c) It is positive if the visual axis is to the nasal side of the optic axis in the object space d) It is very useful in assessing binocular vision anomaliescAn image of a 5 m tall tree is 5.2 mm in the retina. How far (in metres) is the tree in front of the eye? The distance from the nodal point to the retina is 16.67 mm. The rays pass through the nodal point undeviated. Round your answer to two decimal places Hint: Use similar triangles a) 16.03 m b) 15.23 m c) 12.46 m d) 13.21 maWhich of the following statements about the human cornea is true? a) Corneal transparency depends on the regular arrangement of the collagen fibres b) The anterior corneal surface is aspheric c) The cornea is slightly elliptical in shape d) All of the abovedA Rigid Gas Permeable contact lens is placed on the front surface of the cornea such that the light rays are travelling from air (n=1) to the contact lens (n=1.5) into the cornea (n=1.376). What percentage of incident light is reflected at the back surface of the contact lens (i.e. between the contact lens and the cornea)? (2dp) Hint: Reflection = (n' - n/n' + n)2 a) 4% b) 0.019% c) 0.19% d) 0.0019%cWhich of the following statement about corneal asphericity is false? a) It would need to be more spherical peripherally to eliminate spherical aberration b) Normal corneal asphericity eliminates spherical aberration in the retinal image c) The radius of curvature of the human cornea increases from the centre to the periphery d) It is best described by a prolate elliptical conic sectionaA keratometer gives the following information: Power in the vertical meridian 43.5 D @ 90 Power in the horizontal meridian 45 D @ 180 Which one of the following is true? a) The radius of curvature is higher in the horizontal meridian than in the vertical meridian b) The cornea displays against-the-rule astigmatism c) The radius of curvature is shorter in the vertical meridian than in the horizontal meridian d) The cornea displays with-the-rule astigmatismbWhat are the essential factors for corneal transparency in human eyes? a) Regular arrangement of the collagen fibrils b) Integrity of the corneal endothelium c) Protection by the eye lids d) Both a and bdWhich of the following statements about trachoma is false? a) It may lead to blindness b) It manifests as follicles on the inner lid surfaces c) It is mainly caused by poor handling of contact lenses d) It is an infection of the conjunctiva and lidscWhich of these statements about the exit pupil is correct? a) The exit pupil of the eye is smaller than the iris aperture b) The exit pupil is the image of the aperture when seen from the object side c) The exit pupil is slightly in front of the iris aperture d) The exit pupil controls the limiting resolution of the optical systemdWhich of the following statements about the entrance pupil of the human eye is false? a) It is located behind the iris aperture. The entrance pupil is located 0.1 mm in front of the iris aperture and is15% larger than the iris aperture b) It controls the field of view c) It's shape is affected by the field angle (the off-axis viewing angle). d) It controls the amount of light reaching the retina.aT/F: A change in pupil size could affect visual acuityTrueThe maximum refractive index of the crystalline lens is: a) in the capsule b) in the nucleus c) at the equator d) in the cortexbIn an accommodating eye, the power and the radius of curvature of the anterior surface of the lens are +5.6 D and +10.5 mm respectively. If the refractive index of the anterior lens surface is 1.385, what is the refractive index of the aqueous (to 3dp)? Hint: K = n'-n/r a) 1.329 b) 1.326 c) 1.333 d) 1.336bSelect all of the following statements that are correct. During accommodation: Select one or more: a) tension on the ciliary muscle increases b) the ciliary muscle contracts c) the power of the anterior lens surface increases d) the anterior surface moves backwardb and cA patient can clearly read books from 50 cm distance, but prefers to read it from a distance of 30 cm. Patient complains that the letters get blurry as she moves the book closer to the eye from 50 cm (this is your near point of accommodation or NPA). How much power is required so that the patient can clearly read the book from 30 cm distance? Hint: Amplitude of the accommodation (D) = 1/NPA (in meters) a. +3.33 D b. -1.33 D c. +2.00 D d. +1.33 DdThe near point of accommodation (NPA) of a patient is 40 cm. Patient is already using a near add of +1 D. How much near add power is required for the patient to clearly read a book from 20 cm? Hint: Amplitude of the accommodation (D) = 1/NPA (in meters) a) +1.50 D b) +3.00 D c) +2.50 D d) +5.00 DaT/F: The aqueous and vitreous humors are not important for the structural integrity and optical function of the eye.FalseWhat percentage of light incident on the eye is reflected, absorbed or scattered and does not contribute to the retinal image? a) 40% b) 20% c) 60% d) 80%cThe resolution of an optical system may be compromised by: a) aberrations b) focusing error c) diffraction d) all of the abovedIf the diameter of the aperture of an optical system is increased three times, what will the change in spherical aberration be? a) 81 times b) 6 times c) 9 times d) 27 timesaWhich one of these factors does not contribute to the elimination of spherical aberration in the eye? a) The anterior corneal surface b) The gradient refractive index of the crystalline lens c) The anterior surface of the crystalline lens d) The posterior surface of the crystalline lensc"Wavefront error is measured as deviation from a perfect "...?..." at the "...?..."reference sphere at the exit pupilIn the Zernicke coefficient Z(0/2), the numbers 0 and 2 represent "...?..." and "...?..." of the coefficient respectively?azimuthal frequency and radial orderWhat will the size of the retinal Airy disc be (in microns) for light of 650 nm passing through a 6 mm diameter pupil? Hint: d = 1.22*λ*f/y (1 nm = 0.001 microns, 1 mm = 1000 microns). f = distance from the exit pupil to the retina = 20 mm and y is the pupil radius. (to 2dp) a) 2.64 microns b) 5.29 microns c) 3.52 microns d) 4.65 micronsbT/F: The Strehl ratio usually increases with increased pupil size.False - it decreases with increased pupil size because of an increase in aberrationsA light of 600 nm enters an eye through a 5 mm diameter pupil. What is the maximum angle of the converging wavefront to form an Airy disc of diameter 17 microns ? Hint: Use sin of the angle a) 2.46 degree b) 1.64 degree c) 3.42 degree d) 4.82 degreea. Airy disc diameter = 1.22 * λ / sin u (maximum angle of the converging wavefront)Light of 600nm enters an eye with an exit pupil diameter of 5mm. What is the minimum separation (in microns) of two retinal Airy discs for them to be resolved as two? Hint: d = 1.22*λ*f/y (1 nm = 0.001 microns, 1 mm = 1000 microns). f = distance from the exit pupil to the retina = 20 mm y = exit pupil radius. a. 4.2 microns b. 5.86 microns c. 2.93 microns d. 4.76 micronscT/F: If the pupil diameter and the distance from the exit pupil to the retina in an eye are constant, is the retinal Airy disc smaller for blue light than for red light?TrueThe luminance of a small area within an object is 100 cd/m2 compared to its mean background luminance of 200 cd/m2. What is the contrast of the small area compared to its background? a) 200% b) 33% c) 100% d) 75%bT/F: Low refractive errors primarily affect the resolution but not the contrast of a retinal image.FalseWhich of the following statements about the Modulation Transfer Function are false? Select one or more: a) The MTF contains information about diffraction but not aberrations in an optical system b) The MTF contains information about both resolution and contrast of an image c) The MTF contains information about the image quality of an optical system d) The contrast of an image improves with an increase in spatial frequencya and dWhere and at what distance would the far point be for an uncorrected hyperope of 3 D (in cm)? a) 30 cm behind the eye b) 33.33 cm behind the eye c) 30 cm in front of the eye d) 33.33 cm in front of the eyebAn uncorrected hyperopic eye with a 3mm pupil has retinal blur circles 60 microns in diameter. What is the magnitude of uncorrected hyperopia? Hint: b = 20 p K microns a) +2.00 D b) +1.00 D c) +0.50 D d) +3.00 DbWhat is the limiting spatial frequency (in cycles/deg) of an eye viewing a black and white grating with increasing spatial frequency, through a 2.5 mm pupil under a light source of 555 nm? (to 2dp) Hint: f0 = d/(λ* l) l = 20 mm 1 nm = 1e-6 mm 1 mm subtends 3.43 deg to the retina a) 225.23 cycles/deg b) 146.28 cycles/deg c) 65.66 cycles/deg d) 82.64 cycles/degcWhich of the following statements are true? A person with refractive error 0.00 DS/-2.50 DC * 180 has: Select one or more: a) simple myopic astigmatism b) with-the-rule astigmatism c) compound myopic astigmatism d) regular astigmatisma, b and dWhat would the image vergence be for a presbyope who is reading a book 40 cm in front of the eye with his glasses of +1.00 D? a) -1.50 D b) +4.00 D c)+2.50 D d) -2.50 DaA -2.50 D myopic patient has an eye with an axial length of 25 mm. In the subsequent year, the axial length increases by 0.7 mm. What would the expected refractive error then be? a) -4.25 D b) -3.75 D c) -3.25 D d) -5.00 Da - 1 mm defocus = 2.50 D of refractive errorThe cause of the Stiles-Crawford effect is believed to be that "...?..." photoreceptors act as "...?..." to propagate light from the inner to the outer segment"cone" photoreceptors act as "waveguides"What is the Nyquist frequency (in cycles/deg) for a digital camera that has a pixel size of 7 microns? The distance between the exit pupil of the camera and screen is 16.67 mm. If this camera were a human eye, would it able to resolve this spatial frequency at the fovea and why? Hint: After calculating the Nyquist frequency in pixels/mm, calculate the angle subtended (in degrees) by 1 mm of screen at 16.67 mm.T/F: Retinal convergence occurs at the foveaFalseWhich of the following statements are correct? The bipolar and horizontal cells improve the quality of the image in the peripheral retina through: Select one or more: a) Retinal convergence b) Lateral inhibition c) The Stiles-Crawford effect d) ApodisationbT/F: Basic visual information about the colour, contrast and brightness of a visual scene are largely established in the visual cortex.False - They are largely regulated in the retina; however they may get modified in the visual cortex.Which of the following statements about the Snellen chart is false? a) It has no standardization of difficulty in letter recognition b) Recognition of letters is affected by letter and line spacing c) The optotypes only measure visual acuity dominated by low spatial frequencies d) It has a different number of letters in each linecAn individual reads a Snellen letter "E" in the 6/12 line. What would be: a) the visual angle subtended by the full optotype (the 5*5 grid) in minutes of arc? b) the size of the letter (in mm)? Hint: Use the tan of the visual angle at 6 metres distance to calculate the letter size.a) 10 minute of arc b) 17.45mmIf a cone photoreceptor has a radius of 1.5 µm, what is the Nyquist limit of the cone mosaic? a) 5 µm b) 6.5 µm c) 5.5 µm d) 6 µmdConvert Snellen 6/18 acuity to: a) Decimal acuity b) Minimum Angle of Resolution (MAR)a) 0.33 b) 3 minutes of arcWhat is the Snellen conversion for 0.36 logMAR when measured at 3 metres? Hint: MAR = 10logMAR a) 3/6.87 b) 3/5.32 c) 3/7.45 d) 3/8.75aA patient has a Snellen visual acuity of 6/36. On repeating the visual acuity on a logMAR chart, you find that patient is unable to read 4 out of 5 letters in the 0.7 line. a) What is the logMAR equivalent of Snellen visual acuity of 6/36? b) Is it better or worse than the visual acuity measured with the logMAR chart?a) 0.78 b) Snellen > logMART/F: Spurious resolution occurs at high refractive errorsFalseThe Contrast Sensitivity Function (CSF) peaks at the "...?..." range spatial frequencies, where as the Modulation Transfer Function (MTF) peaks at the "...?..." range spatial frequenciesMiddle, lowerAnswer the following questions based on the keratometry value below 46.00 @ 170 44.50 @ 80 a) What kind of astigmatism is this? b) What would be the minus cyl spectacle correction for this astigmatism?a) against the rule astigmatism b) -1.50 X 170T/F: Abbé numbers of two polymers are 30 and 50 respectively. The polymer with Abbé number 50 is likely to exhibit greater chromatic aberration?FalseIf a glass material with a focal length of 20 cm at the middle of the visual spectrum has an Abbé number of 50, what will be the power of this material across the spectrum? Hint: v = Kd/KF - KC a) 0.1 D b) 0.3 D c) 0.4 D d) 0.2 DaIf the aperture (or visual angle) of an optical system increases 3 times, what will be change in chromatic aberration of the system? a) 81 times b) 6 times c) 27 times d) 9 timesdBetween a polymer and a glass of refractive indices 1.586 and 1.802 respectively, which one of them would produce a greater edge reflection?1.802Ostwalt's lens design ignores all the primary aberrations except a) Field curvature b) Distortion c) Coma d) Oblique astigmatismdAccording to Percival Solution "...?..." should be controlled in a way such that the "...?..." falls on the far point sphereOblique astigmatism, circle of least confusionT/F: Most finished lenses have meniscus forms closer to the Wollaston section of the Tscherning ellipseFalse - it's closer to the Ostwalt section of the Tscherning ellipseA man is reading a book from 30 cm using his toric spectacle prescription of -2.00 DS/-1.50 DC*180. a) What kind of astigmatism is this? b) What are the image vergences from the two principal meridians on the spectacle lens? c) The size of the Interval of Sturm (in cm)? Hint: Interval of Sturm = I L1' - L2'/L1'*L2' I The vertical lines in the equation are "modulus lines" (means sign is always positive).a) with the rule astigmatism b) -5.33 D and -6.83 D c) 4.12 cmT/F: K values from a keratometer are 46.00 @ 90 44.00 @ 180 The minus cylindrical spectacle lens correction for this astigmatism is -2.00 * 180TrueAn object placed in the front of an ophthalmic lens of 0.00/-1.50 *90 forms a virtual image at 10 cm for the 90 deg spectacle lens axis (i.e * 90 or the vertical focal line) . Where is the object for this image? a) 11 cm b) -10 cm c) -11.76 cm d) -13.50 cmcLight rays from an object 20 cm in front of a spectacle lens of power +2.00/-3.00 * 135 forms two focal lines in the eye. The diameter of the pupil is 5 mm. What would be: a) The vergence to the Circle of Least Confusion (in D) b) Diameter of the circle of least confusion (in mm) Hint: Circle of least confusion vergence (C) = (L1 + L2)/2 Diameter: d I (L1 - L2) / (L1 + L2) I The vertical lines in the equation are "modulus lines" (means sign is always positive).a) +0.5 D b) 1.66 mmWhich one of the five primary Seidel aberrations primarily affect the image magnification? a) Oblique astigmatism b) Spherical aberration c) Distortion d) Field curvaturec"Hard" progressive lens designs have: Select one or more: a) Concentrated blending regions on either side b) Longer corridor c) Wider distance and reading areas d) Lesser image jump (or swimming effect)a and cThe advantages of "aspheric lenses" are: Select one or more: a) Reduction in spherical aberration b) Reduction in image distortion c) Reduction in centre or edge thickness d) Reduction in weightc and dA base-out prismatic effect is induced on a spectacle lens when a) Optic centre of a plus lens is decentred outwards b) Eyes look inwards in plus lenses with respect to the optic centre c) Eyes look outwards in minus lenses with respect to the optic centre d) All of the abovedA man wearing a spectacle lens of +3 D experiences a prismatic effect of 4.2 ∆ BD when looking through the lenses at a particular gaze. Is he looking up or down with reference to the optic centre of lens and by how much? a) 12.6 cm up from the optic centre of the lens b) 1.4 cm up from the optic centre of the lens c) 1.4 cm down from the optic centre of the lens d) 12.6 cm down from the optic centre of the lensbAn individual has a prescription of -3.00 DS in the right eye and +2.00 DS in the left eye. What will be horizontal prismatic imbalance of the eye when the person looks 10 mm inside from the optic centre from each eye? a) 1 ∆ BI right eye b) 5 ∆ BI right eye c) 1 ∆ BI left eye d) 5 ∆ BO left eyea - RE prismatic effect: 3∆ BI, LE prismatic effect: 2∆ BO. Both prisms will make conjugate movements so the prismatic imbalance: 1∆BI right eye.The right lens of a pair of eyeglass lenses has 2.0 ∆ BU and the left lens has 3.0 ∆ BD. What is the net prismatic effect or prismatic imbalance between these two lenses? a) 5 ∆ BD right eye b) 5 ∆ BD left eye c) 1 ∆ BU left eye d) 1 ∆ BD right eyeb - These prisms will make disjunctive eye movements, so we add the prisms. This can also be written as 5 ∆ BU right eyeFor a myopic eye that can be corrected with a -12.00 D spectacle lens mounted 12 mm in front of the cornea, what would be the required contact lens power? Hint: K = K/1-dK a) -9.64 D b) -10.49 D c) -12 D d) -4.92 DbFront (r1) and back surface (r2) radius of curvature of a plano-convex ophthalmic lens in air (n=1) are 0 mm and -50 mm respectively. The lens has a refractive index of 1.500 and central thickness of 5 mm. What is the front vertex power of the lens? a) +11.50 D b) +14.99 D c) +10.34 D d) -9.68 DcT/F: An uncorrected -2 D myope would require more accommodation to clearly see near objects at 50 cm distance compared to an uncorrected hyperope of +2 D?FalseAn individual reading a book from 50 cm with his spectacle lenses of +5.00 D has an incident vergence of +3.19 D at the cornea (vertex distance is 20 mm). Calculate the increase in corneal incident vergence if the individual slides down his glasses to a vertex distance of 40 mm? a) +0. 17 D b) +0. 34 D c) +0.22 D d) +0. 43 DcThe front (K1) and back (K2) surface powers of an ophthalmic lens are +5.2 D and +10.40 D respectively. The lens has a thickness of 20 mm and n of 1.52. Answer the following questions a) The equivalent lens power is? b) The equivalent focal length is? Hint: Ke = K1 + K2 - d/n *K1*K2a) +14.89 D b) 67.16 mmNodal point of the human eye is located at the: a) Anterior chamber b) Retina c) Posterior pole of the lens d) Corneac