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ICO Visual Sciences practice questions

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Question 1Optics and Refraction

A thin convex lens has a focal length of +25 cm. An object is placed 100 cm in front of the lens. Where is the image formed?

  1. 125 cm in front of the lens
  2. 75 cm behind the lens
  3. 33.3 cm behind the lens Correct answer.
  4. 20 cm behind the lens

Explanation

Using the thin-lens equation 1/f = 1/v − 1/u with sign convention u = −100 cm and f = +25 cm gives 1/v = 1/25 − 1/100 = 3/100, so v = +33.3 cm. The positive sign places a real image behind the lens.

Question 2Optics and Refraction

Which refractive state is defined by parallel incoming light rays coming to focus in front of the retina in an unaccommodated eye?

  1. Hyperopia
  2. Astigmatism
  3. Myopia Correct answer.
  4. Presbyopia

Explanation

Myopia occurs when the eye's refractive power is too strong relative to its axial length, so distant parallel rays focus anterior to the retina. This produces blurred distance vision that concave (minus) lenses correct.

Question 3Optics and Refraction

What is the dioptric power of a lens with a focal length of 40 cm in air?

  1. 4 D
  2. 0.4 D
  3. 40 D
  4. 2.5 D Correct answer.

Explanation

Dioptric power is the reciprocal of focal length in metres: D = 1/f(m). A focal length of 0.40 m gives 1/0.40 = 2.5 D.

Question 4Optics and Refraction

In Gullstrand's schematic eye, what is the approximate power of the anterior corneal surface?

  1. +60 D
  2. +19 D
  3. +8 D
  4. +43 D Correct answer.

Explanation

The anterior corneal surface contributes roughly +43 D, most of which comes from the air–cornea interface. The posterior corneal surface contributes a negative term that reduces total corneal power to about +43 D overall.

Question 5Optics and Refraction

Which surface shape describes a toric contact lens designed to correct regular astigmatism?

  1. Cylindrical front only
  2. Spherical front and spherical back
  3. Toric back and spherical front
  4. Spherical front and toric back Correct answer.

Explanation

A toric lens for astigmatism carries different powers in two principal meridians. Placing the toric surface on the back allows the front surface to remain spherical while the posterior curve neutralizes corneal cylinder.

Question 6Optics and Refraction

What does the term 'vertex distance' refer to in spectacle prescribing?

  1. The separation between the back surface of the lens and the cornea Correct answer.
  2. The distance between the two pupils
  3. The distance from the lens to the centre of rotation of the eye
  4. The thickness of the lens at its edge

Explanation

Vertex distance is measured from the posterior lens surface to the anterior corneal apex. It matters because changing this distance alters the effective power at the eye, especially for higher prescriptions.

Question 7Optics and Refraction

A −5.00 D spectacle lens is worn 14 mm from the cornea. What is the approximate power effectively delivered at the corneal plane?

  1. −5.00 D
  2. −5.38 D
  3. −6.00 D
  4. −4.66 D Correct answer.

Explanation

The effective power formula is F_eye = F/(1 − d·F), with d = 0.014 m and F = −5.00 D. This gives −5/(1 + 0.07) ≈ −4.67 D, so a minus lens moved closer to the eye becomes slightly weaker.

Question 8Optics and Refraction

A patient has a spectacle refraction of +8.00 D at a vertex distance of 12 mm. What is the approximate contact lens power needed?

  1. +8.80 D Correct answer.
  2. +7.20 D
  3. +8.00 D
  4. +10.00 D

Explanation

Converting from spectacle to corneal plane uses F_c = F_s/(1 − d·F_s) with d = 0.012 m. This yields 8/(1 − 0.096) ≈ +8.85 D, so a plus lens must be stronger when moved onto the eye.

Question 9Optics and Refraction

What is the primary optical purpose of a pinhole in front of the eye?

  1. To increase retinal illuminance
  2. To correct chromatic aberration
  3. To widen the field of view
  4. To reduce the blur circle by limiting the effective pupil Correct answer.

Explanation

A pinhole restricts the bundle of rays entering the eye, reducing the diameter of the retinal blur circle from defocus. This improves acuity in refractive error but reduces light reaching the retina.

Question 10Optics and Refraction

Which statement correctly describes spherical aberration in a positive lens?

  1. Marginal rays focus closer to the lens than paraxial rays Correct answer.
  2. Paraxial rays focus closer to the lens than marginal rays
  3. All rays focus at the same point regardless of aperture
  4. It produces lateral colour fringes at the image plane

Explanation

In a positive lens with spherical surfaces, rays passing through the periphery are refracted more strongly and cross the axis nearer the lens than paraxial rays. This longitudinal spread of focus is spherical aberration.

Question 11Optics and Refraction

What is the far point of a myopic eye with a refractive error of −4.00 D?

  1. 100 cm in front of the eye
  2. 25 cm in front of the eye Correct answer.
  3. 40 cm in front of the eye
  4. 4 cm in front of the eye

Explanation

The far point distance equals the reciprocal of the myopic error in dioptres: 1/4.00 = 0.25 m, or 25 cm. At this distance the unaccommodated eye focuses the object clearly on the retina.

Question 12Optics and Refraction

In retinoscopy, a 'with' movement is observed. What does this indicate about the refractive state relative to the working distance?

  1. The eye is hyperopic or myopic less than the working distance Correct answer.
  2. The eye is emmetropic at infinity
  3. The eye is myopic beyond the working distance
  4. The eye has irregular astigmatism

Explanation

A 'with' movement means the far point lies behind the retinoscope's working distance, so the eye is either hyperopic or myopic by less than the working-distance power. Neutralization requires adding plus power until the reflex reverses.

Question 13Optics and Refraction

What is the purpose of a Jackson cross-cylinder during subjective refraction?

  1. To measure amplitude of accommodation
  2. To determine the near point of convergence
  3. To refine the cylindrical axis and power Correct answer.
  4. To assess colour vision

Explanation

The Jackson cross-cylinder presents equal and opposite cylinders in two meridians to compare the patient's response in flipped positions. The endpoint identifies the correct cylinder axis and then the correct cylinder power.

Question 14Optics and Refraction

A reduced-eye model treats the eye as a single refracting surface in air with a power of +60 D. What is its approximate secondary focal length?

  1. 1.67 mm
  2. 6.0 mm
  3. 16.7 mm Correct answer.
  4. 60 mm

Explanation

For a single surface in air, focal length equals 1/F, so 1/60 D = 0.0167 m, or 16.7 mm. This approximates the axial length of an emmetropic reduced eye.

Question 15Optics and Refraction

Which statement about the Stiles–Crawford effect is correct?

  1. Rays entering near the pupil centre are perceived as brighter than marginal rays Correct answer.
  2. It is caused by corneal astigmatism
  3. Rays entering through the pupil margin are perceived as brighter than central rays
  4. It describes the change in refraction with accommodation

Explanation

The Stiles–Crawford effect is the directional sensitivity of cone photoreceptors, so light entering near the pupil centre appears brighter than light of equal intensity entering at the margin. It reflects the waveguide properties of cones.

Question 16Optics and Refraction

What is the primary function of an aphakic spectacle lens with high plus power?

  1. To improve colour discrimination
  2. To replace the lost converging power of the crystalline lens Correct answer.
  3. To increase the eye's axial length
  4. To reduce corneal astigmatism only

Explanation

Aphakia removes the crystalline lens, leaving the eye with insufficient converging power. A high-plus spectacle lens restores the lost power so that images focus on the retina.

Question 17Optics and Refraction

An object is placed at the focal point of a diverging lens. Where does the image form?

  1. At the optical centre
  2. At infinity
  3. It is virtual and located between the lens and the object Correct answer.
  4. At the focal point on the opposite side

Explanation

For a diverging lens, the image is always virtual, erect, and on the same side as the object. When the object is at the focal point, the image lies between the lens and the object and is reduced in size.

Question 18Optics and Refraction

A spectacle lens of −10.00 D is dispensed at a vertex distance of 15 mm. What is the effective power at the corneal plane?

  1. −10.00 D
  2. −8.70 D Correct answer.
  3. −11.76 D
  4. −13.00 D

Explanation

Apply F_c = F/(1 − d·F) with d = 0.015 m and F = −10.00 D: −10/(1 + 0.15) ≈ −8.70 D. The minus lens weakens when moved closer to the eye, so the contact lens power needed is lower in magnitude.

Question 19Optics and Refraction

A patient's keratometry reads 44.00 D at 180° and 46.00 D at 90°. What is the approximate power of a rigid contact lens needed to neutralize the corneal astigmatism at the corneal plane?

  1. +2.00 D cylinder axis 180
  2. −2.00 D cylinder axis 180 Correct answer.
  3. +2.00 D cylinder axis 90
  4. −2.00 D sphere only

Explanation

The difference between the two meridians is 2.00 D, with the steeper meridian at 90°. Neutralizing this with a rigid lens requires a minus cylinder of 2.00 D at the flatter axis, 180°.

Question 20Optics and Refraction

Which factor best explains why high-powered minus spectacle lenses induce a ring scotoma in the peripheral field?

  1. Reduced retinal illuminance at the periphery
  2. Absorption of short wavelengths by the lens material
  3. Increased edge thickness causing prismatic displacement Correct answer.
  4. Chromatic aberration at the lens margin

Explanation

High-minus lenses have thick edges and strong prismatic effect near the periphery, which displaces and magnifies the peripheral field. This produces a ring scotoma where objects are not seen through the lens.

Question 21Physiological Optics and Visual Perception

Which layer of the retina contains the photoreceptor outer and inner segments where phototransduction begins?

  1. The inner plexiform layer
  2. The retinal pigment epithelium Correct answer.
  3. The outer nuclear layer
  4. The nerve fibre layer

Explanation

Phototransduction occurs in the photoreceptor outer segments, which interdigitate with and are supported by the retinal pigment epithelium. The RPE also regenerates 11-cis retinal in the visual cycle, so it is the functional site where the photopigment cascade is completed.

Question 22Physiological Optics and Visual Perception

A patient's visual acuity is measured as 6/60 on a Snellen chart. What does this notation mean?

  1. The patient reads at 60 metres a letter that a standard observer could read at 6 metres
  2. The patient requires a 6-diopter add to read at 60 centimetres
  3. The patient's acuity is 60 per cent of normal for their age
  4. The patient reads at 6 metres a letter that a standard observer could read at 60 metres Correct answer.

Explanation

Snellen notation expresses acuity as the test distance over the distance at which a standard observer could resolve that letter size. Thus 6/60 means the letter read at 6 metres subtends the angle a normal observer would resolve at 60 metres, i.e. reduced acuity.

Question 23Physiological Optics and Visual Perception

In a young emmetropic eye, which structure provides the greatest contribution to the total refractive power?

  1. The crystalline lens
  2. The cornea Correct answer.
  3. The vitreous body
  4. The iris

Explanation

The cornea provides roughly two-thirds of the eye's total refractive power (about 43 D of approximately 60 D), mainly through its anterior surface. The crystalline lens supplies the remaining power and provides accommodation.

Question 24Physiological Optics and Visual Perception

Which photopigment is found in rod photoreceptors and mediates scotopic vision?

  1. Melanopsin
  2. Chlorolabe
  3. Rhodopsin Correct answer.
  4. Erythrolabe

Explanation

Rods contain rhodopsin, composed of the protein opsin and the chromophore 11-cis retinal, which supports dim-light scotopic vision with peak sensitivity near 500 nm. The cone opsins and melanopsin serve other photoreceptor classes.

Question 25Physiological Optics and Visual Perception

Which statement best describes the duplicity theory of vision?

  1. Binocular vision depends on cortical fusion of disparate retinal images
  2. Visual acuity is limited by diffraction at the pupil margin
  3. Rods and cones operate as two receptor systems with different sensitivity and resolution properties Correct answer.
  4. Colour vision depends on three cone types with overlapping spectral sensitivities

Explanation

Duplicity theory holds that vision is served by two receptor systems: highly sensitive, pooled rod pathways for dim light and lower-sensitivity, high-acuity cone pathways for daylight and colour. Their differing convergence and adaptation behaviour explain the shift in visual function with luminance.

Question 26Physiological Optics and Visual Perception

Light entering the eye passes through several structures before reaching the photoreceptors. Which sequence is correct?

  1. Cornea, lens, photoreceptor layer, inner nuclear layer, ganglion cell layer, vitreous
  2. Lens, cornea, vitreous, photoreceptor layer, ganglion cell layer, inner nuclear layer
  3. Cornea, vitreous, lens, ganglion cell layer, photoreceptor layer, inner nuclear layer
  4. Cornea, lens, vitreous, ganglion cell layer, inner nuclear layer, photoreceptor layer Correct answer.

Explanation

The eye is inverted, so light crosses the cornea and lens, traverses the vitreous, then passes through the ganglion cell and inner nuclear layers before reaching the photoreceptors. This arrangement means the neural retina is largely transparent to incoming light.

Question 27Physiological Optics and Visual Perception

What is the approximate diameter of the human pupil under bright daylight in a healthy young adult?

  1. About 2 to 4 mm Correct answer.
  2. About 9 to 10 mm
  3. About 1 to 2 mm
  4. About 6 to 8 mm

Explanation

In bright light the pupil constricts to roughly 2 to 4 mm, balancing diffraction against aberrations for optimal image quality. It dilates to about 6 to 8 mm in darkness.

Question 28Physiological Optics and Visual Perception

A hyperopic eye viewing a distant object must accommodate to see it clearly. What is the optical reason?

  1. The crystalline lens has lost its elasticity and cannot change power
  2. The eye's unaccommodated power is too high for its axial length, so the image forms in front of the retina
  3. The eye's unaccommodated power is too low for its axial length, so the image forms behind the retina Correct answer.
  4. The cornea has excessive astigmatism that blurs all meridians

Explanation

In hyperopia the unaccommodated eye has insufficient power relative to its axial length, so parallel rays would focus behind the retina. Accommodation increases lens power to bring the image forward onto the retina, which is why young hyperopes can compensate until accommodative demand is exceeded.

Question 29Physiological Optics and Visual Perception

A 40-year-old patient has an amplitude of accommodation of 5.00 D. At what near point distance can they sustain clear focus with maximum accommodation, assuming emmetropia?

  1. 20 cm Correct answer.
  2. 5 cm
  3. 25 cm
  4. 50 cm

Explanation

The near point distance equals the reciprocal of the amplitude of accommodation for an emmetropic eye: 1/5.00 D = 0.20 m, or 20 cm. This follows because accommodation adds just enough power to conjugate the near object onto the retina.

Question 30Physiological Optics and Visual Perception

Which statement correctly describes the Purkinje shift?

  1. Colour discrimination improves as luminance decreases
  2. The peak spectral sensitivity moves toward shorter wavelengths as illumination falls to scotopic levels Correct answer.
  3. The peak spectral sensitivity moves toward longer wavelengths as illumination falls
  4. The pupil constricts more to blue light than to red light

Explanation

As light levels drop and rod vision takes over, peak sensitivity shifts from about 555 nm (photopic, cone-dominated) to about 500 nm (scotopic, rod-dominated). This blueward shift is the Purkinje phenomenon and reflects the different spectral tuning of rhodopsin versus cone opsins.

Question 31Physiological Optics and Visual Perception

A distant target subtends 5 minutes of arc at the eye. What is its approximate retinal image size, assuming a simplified eye with a nodal distance of 17 mm?

  1. About 2.5 mm
  2. About 25 mm
  3. About 0.25 mm
  4. About 0.025 mm Correct answer.

Explanation

Retinal image size equals the nodal distance multiplied by the angle in radians. Five minutes of arc is 5/60 × π/180 ≈ 0.00145 rad, and 17 mm × 0.00145 ≈ 0.025 mm.

Question 32Physiological Optics and Visual Perception

Which retinal cells form the direct pathway from photoreceptors to ganglion cells in the fovea?

  1. Amacrine cells
  2. Horizontal cells
  3. Bipolar cells Correct answer.
  4. Müller cells

Explanation

Bipolar cells receive photoreceptor input and synapse onto ganglion cells, forming the vertical through-pathway of the retina. In the fovea this pathway is largely private-line, with one cone driving one midget bipolar and one midget ganglion cell.

Question 33Physiological Optics and Visual Perception

Why does the optic disc produce a physiological scotoma?

  1. It is covered by the macula lutea, which absorbs light
  2. It lacks photoreceptors because ganglion cell axons converge there to exit the eye Correct answer.
  3. It contains only rod photoreceptors and therefore cannot signal colour
  4. It lies outside the binocular field of view

Explanation

At the optic disc the retinal layers are interrupted as ganglion cell axons gather to form the optic nerve, so no photoreceptors are present and light falling there is not detected. The resulting blind spot is normally unnoticed because of cortical filling-in and binocular overlap.

Question 34Physiological Optics and Visual Perception

Which change in the crystalline lens best explains the reduced amplitude of accommodation in presbyopia?

  1. Progressive thinning of the corneal stroma
  2. Loss of photoreceptors in the foveola
  3. Degeneration of the ciliary ganglion
  4. Increased lens nuclear sclerosis with loss of deformability Correct answer.

Explanation

Presbyopia results primarily from age-related hardening and sclerosis of the lens nucleus, which reduces the ability of the lens to change shape under capsular and zonular forces. The ciliary muscle and zonules remain functional, but the lens no longer responds adequately.

Question 35Physiological Optics and Visual Perception

A patient reports that coloured objects appear unusually washed out and that bright lights are uncomfortably glaring. Which cone-related deficit is most consistent with these symptoms?

  1. Selective loss of rod function with preserved cone function
  2. Total loss of the retinal pigment epithelium
  3. Bilateral complete third nerve palsy
  4. Acquired loss of cone function with relatively preserved rod function Correct answer.

Explanation

Reduced cone function impairs colour discrimination and photopic acuity and removes the normal cone-mediated control of light adaptation, producing glare and photophobia. Rod function is relatively spared, so dim-light vision may remain comparatively intact.

Question 36Physiological Optics and Visual Perception

What is the approximate axial length of a typical adult emmetropic eye?

  1. About 24 mm Correct answer.
  2. About 32 mm
  3. About 28 mm
  4. About 18 mm

Explanation

The adult emmetropic eye measures roughly 24 mm axially, with total refractive power near 60 D. Eyes substantially longer tend to be myopic and shorter eyes hyperopic.

Question 37Physiological Optics and Visual Perception

Which statement about the Stiles-Crawford effect is correct?

  1. The effect describes the change in refractive error with accommodation
  2. Light entering near the pupil centre is perceived as brighter than light of equal radiance entering near the margin Correct answer.
  3. The effect is strongest for rod-mediated vision in the dark-adapted eye
  4. Light entering the pupil margin is perceived as brighter than central light

Explanation

The Stiles-Crawford effect is the directional sensitivity of cones: light entering near the pupil centre is more effective than marginal light of the same radiance because cone outer segments act as optical waveguides aligned toward the pupil centre. It is a photopic, cone-mediated phenomenon.

Question 38Physiological Optics and Visual Perception

A patient with a lesion destroying the left optic tract will show which visual field defect?

  1. Binasal hemianopia
  2. Right homonymous hemianopia Correct answer.
  3. Bitemporal hemianopia
  4. Left homonymous hemianopia

Explanation

The left optic tract carries fibres from the temporal retina of the left eye and the nasal retina of the right eye, both of which subserve the right visual hemifield. Destruction therefore produces a right homonymous hemianopia.

Question 39Physiological Optics and Visual Perception

Which factor most directly sets the far point of a myopic eye?

  1. The amount of accommodative convergence available
  2. The density of macular pigment
  3. The degree of axial elongation relative to the eye's refractive power Correct answer.
  4. The diameter of the pupil in dim light

Explanation

The far point is the conjugate point of the retina when accommodation is relaxed, so it is determined by the eye's static refractive error. In myopia, excess power relative to axial length places the far point at a finite distance in front of the eye, and greater elongation brings it closer.

Question 40Physiological Optics and Visual Perception

In a Maxwellian view optical system, which condition is achieved?

  1. The stimulus is presented dichoptically to each eye separately
  2. The pupil is pharmacologically dilated to a fixed diameter
  3. The retinal image is focused at infinity so that accommodation is fully relaxed
  4. A small image of the light source is focused at the pupil so that retinal illumination is independent of pupil size Correct answer.

Explanation

Maxwellian viewing focuses a point source image at the pupil plane so that all rays reach the retina regardless of pupil size, giving controlled retinal illuminance in trolands. This is widely used in psychophysical work requiring precise luminance control.

Question 41Physiological Optics and Visual Perception

A grating stimulus has a spatial frequency of 10 cycles per degree. What is the angular period of one cycle?

  1. 10 degrees
  2. 100 degrees
  3. 1 degree
  4. 0.1 degree Correct answer.

Explanation

Spatial frequency in cycles per degree is the reciprocal of the angular period. Thus 10 cycles per degree corresponds to 1/10 degree, or 0.1 degree, per cycle, equivalent to 6 minutes of arc.

Question 42Physiological Optics and Visual Perception

Which property of retinal ganglion cells is best demonstrated by centre-surround antagonism in their receptive fields?

  1. They respond best to uniform illumination of the whole receptive field
  2. They fire only in response to motion in one direction
  3. They encode colour independently of spatial pattern
  4. They respond best to luminance edges and local contrast Correct answer.

Explanation

Because the centre and surround have opposite sign, uniform illumination largely cancels, whereas a contrast edge falling between centre and surround produces a strong response. This makes ganglion cells edge and contrast detectors rather than simple luminance meters.

Question 43Physiological Optics and Visual Perception

A neutral density filter of optical density 2.0 is placed in a stimulus beam. What is the transmitted fraction of light?

  1. 0.2
  2. 0.1
  3. 0.02
  4. 0.01 Correct answer.

Explanation

Optical density is the negative logarithm (base 10) of transmittance, so transmittance equals 10 raised to the negative density. For density 2.0, transmittance is 10^-2 = 0.01, meaning 1 per cent of light is transmitted.

Question 44Physiological Optics and Visual Perception

Which statement about the cortical magnification factor in primary visual cortex is correct?

  1. It is greatest for the foveal representation and declines with increasing eccentricity Correct answer.
  2. It is greatest for the peripheral representation and declines toward the fovea
  3. It is uniform across the entire retinotopic map
  4. It increases linearly with retinal eccentricity without bound

Explanation

A given angular extent of visual field activates a much larger cortical area near the foveal representation than in the periphery, so cortical magnification is highest at the fovea and falls with eccentricity. This parallels the density of midget ganglion cells and the size of receptive fields.

Question 45Anatomy and Histology of the Eye and Visual Pathway

Which corneal layer consists of a regular arrangement of collagen lamellae interspersed with keratocytes and is the thickest layer of the cornea?

  1. Corneal stroma Correct answer.
  2. Bowman's layer
  3. Descemet's membrane
  4. Corneal epithelium

Explanation

The corneal stroma accounts for roughly 90% of corneal thickness and is built from highly ordered, orthogonally arranged collagen lamellae with flattened keratocytes between them. This regular lattice is what makes the cornea transparent. The epithelium and Descemet's membrane are thin boundary layers, and Bowman's layer is a thin acellular condensation just beneath the epithelium.

Question 46Anatomy and Histology of the Eye and Visual Pathway

Aqueous humor drains from the anterior chamber primarily through which route?

  1. Suprachoroidal space into the vortex veins
  2. Canal of Cloquet into the vitreous
  3. Iridocorneal angle into the ciliary body stroma
  4. Trabecular meshwork into Schlemm's canal Correct answer.

Explanation

The conventional outflow pathway passes through the trabecular meshwork into Schlemm's canal, then into collector channels and episcleral veins. This route carries the majority of aqueous outflow and is the main determinant of intraocular pressure. The uveoscleral route is a minor alternative pathway.

Question 47Anatomy and Histology of the Eye and Visual Pathway

Which retinal cells are the primary photoreceptors responsible for high-acuity, color vision in the fovea?

  1. Bipolar cells
  2. Rod photoreceptors
  3. Amacrine cells
  4. Cone photoreceptors Correct answer.

Explanation

Cones mediate photopic, color vision and are densely packed in the foveola, where acuity is highest. Rods dominate the periphery and function in dim light. Bipolar and amacrine cells are second-order neurons, not photoreceptors.

Question 48Anatomy and Histology of the Eye and Visual Pathway

The optic nerve head corresponds to which retinal landmark?

  1. The ora serrata
  2. The optic disc Correct answer.
  3. The fovea centralis
  4. The macula lutea

Explanation

The optic disc is the site where retinal ganglion cell axons converge and exit the eye, forming the optic nerve head. It lacks photoreceptors, creating the physiological blind spot. The fovea and macula are central retinal regions, and the ora serrata is the anterior termination of the retina.

Question 49Anatomy and Histology of the Eye and Visual Pathway

Which structure separates the anterior chamber from the posterior chamber of the eye?

  1. The lens
  2. The iris Correct answer.
  3. The vitreous body
  4. The ciliary body

Explanation

The iris forms a diaphragm that divides the aqueous-filled space into anterior and posterior chambers. Aqueous flows from the posterior chamber, past the pupillary margin, into the anterior chamber. The lens lies behind the iris, and the ciliary body and vitreous are not the dividing structure.

Question 50Anatomy and Histology of the Eye and Visual Pathway

Which extraocular muscle is primarily responsible for elevation of the eye when it is in the abducted position?

  1. Superior oblique
  2. Inferior rectus
  3. Superior rectus Correct answer.
  4. Inferior oblique

Explanation

With the eye abducted, the visual axis aligns with the muscle plane of the superior rectus, so its contraction produces pure elevation. In adduction, the superior oblique becomes the main elevator. The inferior rectus depresses, and the inferior oblique elevates but is most effective in adduction.