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Anatomy of the Human Visual Pathway

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DOI: 10.1007/978-3-319-52284-5_1

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1

2
Anatomy of the Human Visual
Pathway 1
3 Marek Joukal

4 Abstract
5 Vision is the primary sense in humans. There are approximately one
6 ­million axons in the optic nerve, constituting almost 40% of the total
7 number of axons in all cranial nerves. The primary sensors for sight are
8 the 130 million rods and seven million cones found in the retina. With
9 the release of glutamate, they transform electromagnetic waves of light
10 with a wavelength between 400 and 700 nm to graded changes of the
11 membrane potential. The signal from photoreceptors continues to the
12 bipolar cells and then to the retinal ganglion cells. Their axons pass
13 through the optic nerve, the optic chiasm, form the optic tract, and reach
14 the lateral geniculate body of the thalamus. The axons coming from the
15 nasal hemiretina are crossed in the optic chiasm, while axons from the
16 temporal hemiretina stay uncrossed. Neurons of the lateral geniculate
17 body send their axons to the optic radiation and terminate in the primary
18 visual cortex – the striate area in the ipsilateral occipital lobe where the
19 first analysis of visual information is performed. Further processing
20 takes place in extrastriate visual areas in the occipital, parietal, and tem-
21 poral lobes. The visual pathway shows a precise retinotopical organiza-
22 tion at all levels that gives the anatomical background for symptoms
23 when some part of optic pathway is damaged.

24 Keywords
25 Visual pathway • Vascularization • Pathophysiology • Retina • Optic nerve
26 • Optic chiasm • Optic tract • Lateral geniculate • Optic radiation • Striate
27 cortex • Extrastriate cortex

M. Joukal, MD, PhD

Department of Anatomy, Division of Neuroanatomy,
Faculty of Medicine, Masaryk University,
625 00 Brno, Czech Republic
e-mail: mjoukal@med.muni.cz

© Springer International Publishing AG 2017 1

K. Skorkovská (ed.), Homonymous Visual Field Defects, DOI 10.1007/978-3-319-52284-5_1
 2 M. Joukal

28 1.1 Introduction of ganglion cells pass through the optic nerve, 32

optic chiasm, and optic tract. The fourth neuronal 33
29 The visual pathway is composed of four neuronal elements are found in the lateral geniculate body; 34
30 elements. Photoreceptors, bipolar cells, and reti- their axons form the optic radiation and terminate 35
31 nal ganglion cells are found in the retina. Axons in the primary visual cortex (Fig. 1.1). 36

Retina
I. - III.

Optic nerve

Optic chiasma

Optic tract

Lateral
geniculate
IV. body

Optic radiation

Striate area

[AU1] Fig. 1.1  Schematic drawing of the visual pathway and its neuronal composition
 1  Anatomy of the Human Visual Pathway 3

37 1.2 The Retina light hitting the centre and inhibited by light hit- 52
ting the peripheral area are called ON-neurons. 53
38 The retina is the innermost thin layer of tissue Neurons that have the opposite reaction to the 54
39 covering the back of the eye. It develops from the light are known as OFF-neurons. 55
40 optic vesicles of the hindbrain. Each optic vesicle
41 “caves in” to form the optic cup, which consists
42 of two layers and is connected to the developing 1.2.1 T
 he First Neuron: Rods 56
43 brain by the optic stalk. The outer layer of the and Cones 57
44 optic cup becomes the pigment epithelium of
45 the retina, and the inner layer differentiates into the The outer part of the retina adjacent to the 58
46 complex neural layer of the retina. The optic stalk choroid is pigment epithelium composed of 59
47 becomes the optic nerve. cuboidal cells with pigmented granules in 60
48 The retina is functionally divided into small their cytoplasm. Internal to this layer is a layer 61
49 spots called receptive fields, composed of the cir- of photoreceptors. There are two types of pho- 62
50 cular receptive field centre and the peripheral toreceptors in the retina, the rods and cones, 63
51 area (Fig. 1.2). The neurons that are excited by which represent the first neuron of the optic 64

Receptive centre Peripheral area

Photoreceptors

Fig. 1.2  The receptive

field centre provides a
direct connection
among the
photoreceptors and
bipolar cells, while the
signal from the
photoreceptors in the
peripheral area passes Horizontal cell
through horizontal cells
to the bipolar cells
Bipolar cell
(Adapted from Dubový
and Klusáková [2], with
permission)
 4 M. Joukal

Light which is an aldehyde of the vitamin A molecule. 72

Seven million cones are found in the central 73
fovea of the retina. They are responsible for 74
vision in strong light (photopic vision) and 75
perception of shape and color. The photopig- 76

Ganglion cell ment of cones differs slightly from rhodopsin 77

in the structure of the opsin molecules. There 78
are three types of cone opsin and thus three 79
Amacrine cell kinds of cones absorbing light of different 80
wavelengths. One kind of cone responds best 81
to light in the blue part of the spectrum (maxi- 82
mum wavelength 420 nm), another in the 83
green part (maximum wavelength 530 nm), 84
Bipolar cell
and the third in the red part (maximum wave- 85
length 560 nm). Each photopigment is 86
bleached not only by light with wavelengths to 87
which it is maximally sensitive but also by 88

Horizontal cell
stronger light with shorter and longer wave- 89
lengths; thus, one kind of cone alone cannot 90
inform about color [1–4]. 91

Photoreceptor In addition to rods and cones there is a third 92

cell type of photosensitive cell in the retina – retinal 93
ganglion cells expressing the photopigment mela- 94
nopsin. They give rise to the retinohypothalamic 95
Outer segment tract and were identified only recently. These cells 96
convey the general level of environmental illumi- 97
nation to the suprachiasmatic nucleus of the hypo- 98

Pigment thalamus where the primary circadian pacemaker 99

epithelium is localized. They are also connected with the pre- 100
tectal area of the midbrain and are involved in the 101
pupillary light response [5, 6]. 102

Fig. 1.3  A highly simplified picture of cellular connec- 1.2.2 Second Neuron: Bipolar Cells 103
tions in the retina (Adapted from Brodal [1] by permission
of Oxford University Press, USA)
The bodies of bipolar cells form the inner nuclear 104
layer of the retina. Their dendrites are in contact 105
with the base of the rods and cones. In cones 106
65 pathway (Fig. 1.3). The retina contains 130 there are two kinds of bipolar cell: ON bipolar 107
66 million rods, which are much more sensitive cells are excited when light hits the photorecep- 108
67 than the cones and react to extremely small tor and are inhibited in the dark. The second type 109
68 amounts of light. They are responsible for of bipolar cell is excited in the dark and inhibited 110
69 vision when the light is dim – scotopic vision. in light; therefore, they are called OFF bipolar 111
70 Rods contain the ­photopigment rhodopsin – cells. In rods all bipolar cells are hyperpolarized 112
71 composed of a protein part, opsin – and ­retinal, when the light hits the rods (Fig. 1.4). 113
 1  Anatomy of the Human Visual Pathway 5

OFF - ganglion cell ON - ganglion cell

Amacrine cell

OFF bipolar

ON bipolar

Horizontal cell

Cone

Rod

Fig. 1.4  Schematic drawing of two types of bipolar cells and their connection with the ganglion cells of the retina
(Adapted from Brodal [1] by permission of Oxford University Press, USA)

114 1.2.3 T
 he Third Neuron: Retinal the receptive field. This inhibition is processed 121
115 Ganglion Cells via horizontal cells [1–4]. Apart from the divi- 122
sion of ganglion cells to ON and OFF, anatomic 123
116 The dendrites of ganglion cells are in contact studies of the monkey found that these cells dif- 124
117 with ON or OFF synaptic centers via axons of fer greatly in size. Therefore, we can distin- 125
118 bipolar cells. The ON ganglion cells are excited guish the M-cells (magnocellular) and P-cells 126
119 when the light hits the centre of the receptive (parvocellular). The P-cells have smaller cell 127
120 field and inhibited by light on the periphery of bodies, a less extensive dendritic tree, and 128
 6 M. Joukal

a 5,7 parietal cortex a 21, 22 inferotemporal cortex

a 17 INTER BLOB BLOB

Lateral
geniculate M P
body

III. M III. P

II. II.
Retina

I. I.

Fig. 1.5  Schematic diagram of the magnocellular (M) and parvocellular (P) retinal ganglion cells projection through
the lateral geniculate body to the visual cortex

129 a thinner axon than M-cells. The P-cells are h­ orizontal cells. Amacrine cells are intercalated 144
130 most numerous; they constitute about 80% of between bipolar cells and ganglion cells within 145
131 all ganglion cells in the retina. A major differ- the inner nuclear layer. They are in contact with 146
132 ence in comparison to M-cells is that the P-cells the axons of the bipolar cells and dendrites of the 147
133 respond preferentially to light with a particular ganglion cells. Many bipolar cells of rods exert 148
134 wavelength. This means that P-cells are color- their effect on ganglion cells only or mainly via 149
135 specific, whereas M-cells do not have such amacrine cells. Amacrine cells are responsible 150
136 specificity. Axons of M- and P-cells terminate for interaction between ON and OFF synaptic 151
137 on M- and P-neurons of the lateral geniculate centers, which is important for the increase of 152
138 body, respectively (Fig. 1.5) [7]. contrast and the detection of motion. The hori- 153
zontal cell processes establish contact with the 154
inner segments of the photoreceptors and with 155
139 1.2.4 Interneurons of the Retina the dendrites of bipolar cells. Therefore, they 156
serve for regulation of transmission from the 157
140 There are two kinds of interneurons in the photoreceptors to the bipolar cells. Horizontal 158
141 ­retina that are responsible for visual information cells are responsible for the typical receptive 159
142 processing based on modulation of bipolar
­ fields of the bipolar cells and ganglion cells with 160
143 and ganglion cells activity – amacrine cells and central excitation and lateral inhibition. 161
 1  Anatomy of the Human Visual Pathway 7

162 There are two parallel signal pathways from cilioretinal arteries that are branches of ciliary 187
163 the cones. The ON ganglion cells increase the arteries. This variant is found in approximately 188
164 impulse frequency when the light hits the cones 20% of the population (Fig. 1.6) [3, 8, 9]. 189
165 to which they are connected. The OFF gan- Each segment of the capillary network is 190
166 glion cells are stimulated in darkness. This drained by retinal venules that continue into pro- 191
167 organization increases the range of light inten- gressively larger vessels. These venules consti- 192
168 sities more than if there were only one channel. tute the central retinal vein that exits the eyeball. 193
169 The functional connection of neurons in the Latent collaterals between the central retinal 194
170 retina comes from photoreceptors to bipolar vein and the choroidal venous drainage can be 195
171 cells and then to ganglion cells. The axons of located at the border between the optic nerve and 196
172 ganglion cells form the optic nerve. Comparison the retina [10]. 197
173 of the number of photoreceptors (more than
174 100 million) and ­ganglion cells (one million)
175 shows that there is a large convergence of sig- 1.2.6 Lesions of the Retina 198
176 nals in the retina. In addition to the direct con-
177 nection of neurons, the signal is also conducted The symptoms of partial damage or interruption 199
178 via interneurons [1–4]. in any part of the optic pathway correspond to 200
anatomical arrangement of cells and fibers. 201
Lesions of the retina or optic nerve prevent the 202
179 1.2.5 Blood Supply of the Retina transduction of signals from the eye to higher 203
­levels of the optic pathway; therefore, it induces 204
180 The retina is supplied by the central artery that is monocular blindness (Fig. 1.7) [1, 3, 11]. 205
181 a branch of the ophthalmic artery. The central
182 retinal artery arises inferiorly to the optic nerve
183 and runs within the nerve to the eyeball. It
184 emerges at the optic disc where it divides into the
185 terminal branches for each quadrant of the ret-
186 ina. The retina can also be supplied by variant

1. Internal carotid artery

2. Anterior cerebral artery
3. Anterior communicating artery
4. Posterior communicating artery
5. Basilary artery 14
13
6. Posterior cerebral artery
7. Posterior choroidal artery 3
8. Calcarine artery 12
9. Middle cerebral artery 2
11
Optic nerve
10. Anterior choroidal artery
11. Superior hypophyseal artery 1
12. Ophthalmic artery
9
13. Central retinal artery 10
14. Cilio-retinal arteries 4
5

7
6

Fig. 1.6  A simplified schematic drawing of visual path- Fig. 1.7  Lesion of the optic nerve or retina causes mon-
way vascularization ocular blindness
 8 M. Joukal

206 1.3 Optic Nerve geniculate body. The remaining 10% of axons 246
constitute the medial root of the optic tract. 247
207 The axons of the retinal ganglion cells run toward These axons terminate in the tectum of the mes- 248
208 the posterior pole of the eye and pass through the encephalon (retinotectal tract), especially in the 249
209 wall of the eyeball at the optic papilla. The axons superior colliculus and the pretectal nuclei. 250
210 then constitute the optic nerve that is in fact a These fibers are important for optic reflexes, 251
211 protrusion of the hindbrain. The optic nerve is such as pupillary reflex or vestibulo-ocular 252
212 covered by extensions of the cranial meninges reflex. Some fibers of the optic tract terminate in 253
213 and subarachnoid space filled with cerebrospinal the hypothalamus (retinothalamic tract) where 254
214 fluid. The nerve passes posteromedial in the orbit they contribute to regulation of circadian rhythms 255
215 toward the optic canal. The optic nerve emerges [1, 4, 15, 16]. 256
216 in the middle cranial fossa after exiting the optic
217 canal [1–4].
1.4.1 B
 lood Supply of the Optic 257
Chiasm 258
218 1.3.1 B
 lood Supply of the Optic
219 Nerve The optic chiasm is highly vascularized. The 259
main blood supply is provided by the branches of 260
220 According to the topography of the optic nerve the internal carotid artery, anterior communicating 261
221 it can be divided into proximal (intracranial), artery, and anterior cerebral artery (see Fig. 1.6). 262
222 middle (intracanalicular), and distal (intraor- Some small branches supplying the chiasm come 263
223 bital) parts. The blood supply of these parts is from the middle cerebral artery, posterior com- 264
224 provided by different arteries (see Fig. 1.6). The municating artery, and anterior choroidal artery 265
225 intracranial as well as intracanalicular parts of [10, 17, 18]. 266
226 the optic nerve are supplied by the superior
227 hypophyseal artery, a branch of the internal
228 carotid artery. The contributions of the ophthal- 1.4.2 Lesions of the Optic Chiasm 267
229 mic artery to this part of the nerve are negligi-
230 ble. The intracanalicular part is mainly supplied In a contrast to lesions of the optic nerve, where 268
231 by the intrinsic capillary network from the supe- monocular blindness occurs, lesions in the optic 269
232 rior hypophyseal artery. This supply may be chiasm produce various visual symptoms accord- 270
233 easily interrupted by compression on or swell- ing to their localization. These lesions can be 271
234 ing of the optic nerve in the very narrow optic divided into those that affect the anterior angle, 272
235 canal. The most distal part (intraorbital) part is the body, and the posterior angle of the optic chi- 273
236 supplied by the ophthalmic artery [12]. asm [19]. The anterior angle lesions, where the 274
fibers from the nasal hemiretina are localized, 275
induce varying degrees of temporal defect in the 276
237 1.4 Optic Chiasm and Optic Tract ipsilateral eye. The specific visual field defect is 277
called “junctional scotoma” and affects the con- 278
238 The optic nerves of both sides meet in the optic tralateral superior temporal field. In case of exten- 279
239 chiasm, where the fibers of the nasal hemiretinae sive lesion in the anterior angle of the optic chiasm 280
240 cross to the contralateral optic tract, while the monocular blindness can also occur [11, 20]. 281
241 axons of the temporal hemiretinae stay Bitemporal hemianopia is a specific symptom of 282
242 uncrossed. There is a slight preponderance of lesions located in the body of the optic chiasm 283
243 crossed to uncrossed fibers (53:47) [13, 14]. The where the crossed fibers from the nasal hemireti- 284
244 main ­portion of all axons (90%) forms the lateral nae of both eyes are affected (Fig. 1.8) [1, 19]. 285
245 root of the optic tract and continues to the lateral Posterior angle lesions in the optic chiasm are 286
 1  Anatomy of the Human Visual Pathway 9

Bitemporal hemianopsia Homonymous hemianopsia

Optic tract
Optic chiasm

Fig. 1.8  Bitemporal hemianapia is caused by lesion in Fig. 1.9  Lesion of the visual pathway behind the chiasm
the optic chiasm produces homonymous hemianopia

287 expressed by bitemporal hemianopic scotomas. they come from the p­osterior communicating 304
288 Such defects may be mistaken for cecocentral artery. Within the optic tract a very rich microvas- 305
289 scotomas and attributed to a toxic, metabolic, or cularization provides possible collateral blood cir- 306
290 even hereditary process rather than to a tumor; culation [21]. The superior part of the optic chiasm 307
291 however, in true bitemporal hemianopic scotomas and the optic nerve is drained to the venous plexus 308
292 color perception and visual acuity are spared, in that is opened to the anterior cerebral veins. The 309
293 contrast to that in central scotomas [19]. inferior part is drained by the venous plexus that 310
empties into the basal vein [10]. 311

294 1.4.3 B
 lood Supply of the Optic
295 Tract 1.4.4 Lesions of the Optic Tract 312

296 The optic tract is mainly supplied by the anterior Homonymous visual field defects occur when the 313
297 choroidal artery (branch of the internal carotid optic pathway is damaged posteriorly to the optic 314
298 artery) and by the posterior communicating artery chiasm. Lesions in the optic tract prevent trans- 315
299 (see Fig. 1.6). The anterior half is supplied by both duction of the signal from the ipsilateral temporal 316
300 arteries, while the posterior half is supplied only and contralateral nasal hemiretina, i.e., if the 317
301 by the anterior choroidal artery. The collaterals of lesion is found in the right optic tract, the patient 318
302 the anterior choroidal artery are found on the tem- is blind in the left half of the visual field (Fig. 1.9) 319
303 poral side of the optic tract, while on the nasal side [1, 11]. This finding, known as homonymous 320
 10 M. Joukal

321 hemianopia, is rare in the optic tract and, together magnocellular layers. The posterior four layers are 331
322 with lesions of the lateral geniculate nucleus, rep- composed of small cells and are called parvocel- 332
323 resent only 5–11% of total cases [11, 22, 23]. lular layers. Large retinal ­ganglion cells (M-cells) 333
send their axons to the magnocellular layers of the 334
lateral geniculate body, whereas the small retinal 335
324 1.5 Lateral Geniculate Body ganglion cells (P-cells) send their axons to the par- 336
vocellular layers. Three layers receive the crossed 337
325 The lateral geniculate body is part of the hindbrain axons while the other three layers receive the 338
326 and contains bodies of fourth neurons of the optic uncrossed axons. The bodies of neurons in layer 2, 339
327 pathway. It is composed of six cellular layers 3, and 5 receive the information from the ipsilat- 340
328 (1–6 in ventrodorsal direction) separated by axons eral temporal hemiretina, while layers 1, 4, and 6 341
329 and dendrites. The two anterior layers are formed receive information from the contralateral nasal 342
330 by bodies of large neurons and are therefore called hemiretina (Fig. 1.10). 343

n.opticus

chiasma
opticum

tr.opticus

Fig. 1.10 Schematic P
drawing of the lateral
geniculate body P
organization. Six cellular 6
5 P
layers (1–6) formed by
magnocellular (M) and C 4 P
parvocellular (P) cells
I 3 M
connect with the ipsilateral 2 M
temporal hemiretina and C
I 1
contralateral nasal I
hemiretina C
 1  Anatomy of the Human Visual Pathway 11

344 1.5.1 B
 lood Supply of the Lateral 1.6 Optic Radiation 387
345 Geniculate Body
Neurons of the lateral geniculate body send their 388
346 The lateral geniculate body has dual bloody axons to the cortex. These axons form the optic 389
347 ­supply: from the anterior choroidal artery (branch radiation as a part of the posterior limb of the 390
348 of the internal carotid artery) and two or three internal capsule. The inferior fibers contain infor- 391
349 posterior choroidal arteries that are branches of mation about the superior visual field and ini- 392
350 the P2 segment of the posterior cerebral artery tially pass anteriorly as the Meyer loop. The 393
351 [24]. These arteries form a network on the surface Meyer loop passes lateral to the anterior portion 394
352 of the lateral geniculate body and can provide of the temporal horn of the lateral ventricle, then 395
353 ­collateral blood circulation in case of occlusion of courses through the temporal lobe to terminate in 396
354 one artery. The superficial capillary network gives the primary visual cortex below the calcarine fis- 397
355 off small arterioles that directly supply the lateral sure in the medial surface of the occipital lobe. 398
356 geniculate body [21]. Each six layers of the lateral The superior tracts contain information regarding 399
357 geniculate body contain an individual capillary the inferior visual field, travel through the pari- 400
358 network connected by anastomoses. etal lobe, and terminate in the superior part of the 401
359 The lateral and medial horn of the lateral primary visual cortex above the calcarine fissure 402
360 geniculate body is supplied by the anterior cho- [11, 16, 30]. 403
361 roidal artery, whereas the hilum by the poste-
362 rior choroidal artery (branch of the posterior
363 cerebral artery). In more than 48% of individu- 1.6.1 B
 lood Supply of Optic 404
364 als the lateral geniculate body receives blood Radiation 405
365 also from other branches of the posterior cere-
366 bral artery such as the hippocampal, anterior The optic radiation is supplied by three main 406
367 temporal, posterior temporal, and parietooc- arteries: anterior choroidal artery, middle cere- 407
368 cipital artery, and the middle posterior choroi- bral artery, and posterior cerebral artery (see 408
369 dal artery [25]. Fig. 1.6). The anterior segment of the optic radi- 409
ation receives branches from the anterior 410
­choroidal artery, middle cerebral artery, thal- 411
370 1.5.2 L
 esions of the Lateral amogeniculate arteries, and posterior and lateral 412
371 Geniculate Body choroidal arteries. The middle segment of the 413
optic radiation is supplied by arterial branches 414
372 Lesions of the lateral geniculate nucleus are from the middle cerebral artery, parietooccipital 415
373 found less frequently than those of the optic tract, artery, and anterior and middle temporal arter- 416
374 and most frequently are caused by infarction of ies. Lastly, the posterior segment of the optic 417
375 the anterior or lateral choroidal arteries [24]. The radiation receives branches from the middle 418
376 lateral and medial portions of the lateral genicu- cerebral artery and the posterior cerebral artery. 419
377 late nucleus represent the superior and inferior All these branches penetrate directly through 420
378 hemifields, respectively. These portions are sup- the optic fibers [31]. 421
379 plied mainly by the anterior choroidal artery;
380 therefore, its occlusion causes a quadruple sec-
381 toranopia that is an incomplete wedge-shaped 1.6.2 Lesions of the Optic Radiation 422
382 homonymous hemianopia [26, 27]. The hilum of
383 the LATERAL GENICULATE nucleus is sup- The fibers of the optic radiation have retinotopic 423
384 plied by the lateral choroidal artery; its occlusion organization, thus even small structural lesions 424
385 induces homonymous horizontal sectoranopia produce circumscribed, sharply marginated, abso- 425
386 [11, 28, 29]. lute, congruent homonymous contralateral visual 426
 12 M. Joukal

Scotoma 1.7 The Visual Cortex 440

1.7.1 Primary Visual Cortex 441

The primary visual cortex or striate area (also 442

known as V1 or visual area 1) is localized 443
alongside the calcarine sulcus on the medial 444
side of the occipital lobe. The striate area has 445
been named according to the white stripe of 446
myelinated axons that runs parallel to the cor- 447
tical surface. The striate area contains the 448
­retinotopic map of the visual field and approx- 449
imately 50% of that area represents only the 450
central 5° of the visual field (Fig. 1.12) [32]. 451
The primary visual cortex is formed by six 452
layers of neurons (laminae I-VI) as part of the 453
neocortex and forms the area 17 of Brodmann. 454
The axons of the lateral geniculate body termi- 455
nate mainly on the lamina IV where the infor- 456
mation is transmitted to the other cortical 457
centers. The cells of the striate area with simi- 458
Striate area lar orientation selectivity are organized to col- 459
umns perpendicular to the surface of the 460

Fig. 1.11  Lesion in the optic radiation or striate area

cortex. The striate area can be divided into 461

causes circumscribed, congruent, contralateral, homony- three basic systems responsible for processing 462
mous visual field defects (scotomas) particular modalities of vision. The first sys- 463
tem is formed by three cortical columns that 464
are specific for perception from the left and 465
427 field defects (Fig. 1.11) [32]. The superior fibers right eyes. This organization is important for 466
428 carry information from the inferior visual field, binocular vision and basic for depth percep- 467
429 and the inferior fibers inform about the superior tion. The second system is composed of cells 468
430 visual field. Lesions in the inferior temporal com- that receive information from identical ­retinal 469
431 ponents of the optic radiation result in a contralat- positions and have the same axes of orienta- 470
432 eral superior quadrantanopia or wedge-­ shaped tion; this provides the perception of move- 471
433 defect (“pie-in-the-sky”). Damage to the superior ment. The third system is organized into 472
434 parietal fibers of the optic radiation induces con- columns that form the irregular spots on the 473
435 tralateral inferior quadrantanopia or lower transverse sections called “blobs”. They are 474
436 homonymous field defect [19]. Homonymous
­ responsible for perception of color. Between 475
437 hemianopia with macular splitting can occur in the areas of blobs are localized neurons that 476
438 the case of large lesions of the optic radiation, are called “interblobs” specific for the percep- 477
439 often caused by infarction [22]. tion of shape (Fig. 1.13) [1–3, 33, 34]. 478
1  Anatomy of the Human Visual Pathway 13

Fig. 1.12  The cortical

localization of the
visual pathways and
visual field showing the
highly magnified foveal
representation in the
cortex, which covers
approximately half
of the visual cortex

Calcarine sulcus

Visual field

Retina

Ipsilateral Contralateral

1.7.2 Extrastriate Visual Cortex 479

Interblobs Blobs
Information from the primary visual area is sent 480
to the associated cortical centers called extrastri- 481
ate visual areas where the final processing of 482
vision takes place. As mentioned previously, the 483
primary visual cortex is also known as V1; the 484
Left parts of the extrastriate visual cortex are called 485
Righ
t V2–V5. They are composed of Brodmann areas 486
Left
Rig 18 and 19 with several subdivisions [10]. 487
ht
Information from the primary visual cortex 488
reaches the extrastriate areas via the ventral and 489
Fig. 1.13  Schematic picture of the columnar organiza-
tion in the striate cortex (Adapted from Dubový and dorsal stream (Fig. 1.14). The ventral stream 490
Klusáková [2], with permission) passes downward from the occipital lobe to the 491
 14 M. Joukal

Parietal cortex
(area 7)
Prefrontal
cortex

MT
V4 V2
V1

Extrastriate cortex
(inferotemporal)

Fig. 1.14  Ventral and dorsal pathways from the striate to of movement and space (Adapted from Brodal [1] by per-
the extrastriate cortex. The ventral stream is important for mission of Oxford University Press, USA)
object identification, and the dorsal stream for perception

492 temporal lobe and carries information about object superior branches that accompany the superior 517
493 identification including shape, contrast, and color, and inferior margin of the calcarine sulcus, 518
494 also called the “what” pathway. Information about respectively [35]. 519
495 spatial features and movement, called the “where” The calcarine artery is supplemented by the 520
496 pathway, runs in the dorsal stream upward from parietooccipital artery and/or the posterior 521
497 the occipital lobe to the parietal lobe [1–3, 33]. temporal artery that are direct branches of the 522
posterior cerebral artery. Furthermore, there 523
are many possible anastomoses between the 524
498 1.7.3 B
 lood Supply of the Visual cortical branches (intratree anastomoses) of 525
499 Cortex the posterior cerebral artery and between the 526
posterior cerebral artery and middle cerebral 527
500 The occipital lobe of the forebrain is supplied artery [10] supplying, in particular, the macu- 528
501 by cortical branches of the posterior cerebral lar visual cortex. 529
502 artery (see Fig. 1.6). The calcarine artery and The inferior surface of the occipital lobe is 530
503 the parietooccipital artery arise from the distal drained via inferior occipital veins to the occipi- 531
504 part (P3) of the posterior cerebral artery. The tobasal vein, which opens to the lateral tentorial 532
505 visual cortex that is localized alongside the cal- sinus. The blood drainage of the lateral surface of 533
506 carine sulcus is mostly supplied by the calcarine the occipital lobe is provided by superficial corti- 534
507 artery. This artery originates directly from the cal veins that open to the occipital vein. The 535
508 posterior cerebral artery in 78% of individuals, occipital vein faces anteriorly and often opens to 536
509 from the parietooccipital artery in 16%, and the superior sagittal sinus. 537
510 from the posterior temporal artery in 6%. The
511 calcarine artery in 75% of cases does not follow
512 the calcarine sulcus. It can be localized at the 1.7.4 L
 esions of the Primary Visual 538
513 floor of the calcarine fissure, on the medial sur- Cortex 539
514 face of the occipital lobe paralleling the fissure,
515 or upward and posterior to the calcarine sulcus. Lesions of the occipital lobe produce almost 40% 540
516 Sometimes the artery splits into inferior and of homonymous hemianopias, and 70% of them 541
 1  Anatomy of the Human Visual Pathway 15

542 are arterial infarctions [23]. Lesions of the occip- could be combined with prosopagnosia, superior 587
543 ital pole are responsible for contralateral homon- quadrantanopia, or topographagnosia, when the 588
544 ymous scotomas that are extremely congruous. patient is lost in familiar surroundings. The 589
545 Lesions that are localized more anteriorly involve destruction of bilateral lingual and fusiform gyri 590
546 the peripheral vision; in particular, lesions of the by infarction of the posterior cerebral artery 591
547 most anterior edge of the striate cortex can pro- results in prosopagnosia, when the patient is 592
548 duce monocular peripheral temporal defects, the unable to identify and recognize familiar faces. 593
549 so-called temporal crescent. The lesions that Infarction in the left posterior cerebral artery ter- 594
550 affect the area above and below the calcarine sul- ritory destroys the inferior occipitotemporal 595
551 cus cause the inferior and superior quadran- region, resulting in acquired alexia, which is 596
552 tanopias, respectively [11, 22]. Bilateral lesions expressed by loss of the ability to read in previ- 597
553 of the occipital lobe simultaneously, or more usu- ously literate subjects with normal visual acuity 598
554 ally sequentially, can induce any combination of [1, 11, 37]. 599
555 bilateral homonymous hemianopia with or with- Lesions of the dorsal stream produce Bálint 600
556 out macular sparing and various degrees of con- syndrome, which was originally described in 601
557 gruency [11, 19]. When the striate cortex is patients with bilateral parietal lobe lesions but 602
558 totally damaged, mostly from the cerebrovascu- also in patients with bifrontal lesions. This syn- 603
559 lar lesions, cortical blindness occurs [36]. drome is a combination of optic apraxia, the 604
560 The macular area of the visual cortex is local- inability to shift the gaze voluntarily; simultanag- 605
561 ized in a “watershed area” on the boundary nosia, the inability to comprehend the totality of 606
562 between the areas perfused by the posterior and the picture or scene; and optic ataxia that is 607
563 the middle cerebral arteries (see Fig. 1.6). The expressed by the impairment of visually guided 608
564 visual cortex subserving midperipheral and grasping or reaching, despite adequate strength 609
565 peripheral fields is supplied only by the posterior and coordination [11, 38, 39]. 610
566 cerebral artery. Therefore, during times of block-
567 age of one of the arteries that supply the water- Conclusion 611
568 shed area, such as in atherosclerosis, the Organization of the visual pathway shows a 612
569 ipsilateral macular cortex may be spared from precise retinotopical organization at all levels. 613
570 ischemia by virtue of its dual supply. This may be Homonymous visual field defects arise due to 614
571 an explanation for the phenomenon of macular the damage of the optic pathway behind the 615
572 sparing. On the other hand, when there is gener- optic chiasm by various pathological pro- 616
573 alized hypoperfusion state (e.g. in heart failure or cesses. Knowledge of the visual pathway anat- 617
574 intraoperative hypotension), the first area of the omy and its peculiarities enables good 618
575 visual cortex to be affected is that supplied by ter- correlation with clinical symptoms of visual 619
576 minal branches, the macular visual cortex, result- pathway damage and provides the background 620
577 ing in a central homonymous hemianopia. for appropriate diagnostic and therapeutic 621
procedures. 622

578 1.7.5 L
 esions of the Extrastriate
579 Cortex
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AU1 We have relabeled the Figs. 1.1 to 1.14. Please confirm is this fine.

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