Physiologic optics : dioptrics of the eye, functions of the retina, ocular movements and binocular vision

Front matter

5 ue ai EGR AON Shea ci oo

SRAM.

SFG are : ; : RAD EIST AIST ERE ce OARS SCE SEEN S Sees SENSU EN OTA ATS ey on METRO a he etieh ot : SORE ASE Speen SD 3 i a RESEREAE cs we

CHAPTER I OPTIC PRINCPLES ge EET ET EEE Eee Ce ee Tere ee ere

Heetilinear Propagation of Light ........c.cccccccsccecccene ee Oe NIA ok. coc den cavecinveds sa beeandeeacnn NI bo aad .n b.0 alc.aaes ta ks o'o.0 tnd bee eae waueine Plane Mirrors. Construction of the Image.................. i tens POON Svidos en ceackcsataoon cevurpeve tess i Cn: eck cede eherevge Ge iks cee 0e var euaeahes Ken kent CE > SER Cou tine Winiv balda Vay Scan cede Cathe ae ee ee IL. Nek aoc gcncdhvebarasdeelveun cannes diisie ava Cad vers Quantity of Light Reflected. Total Reflection................ Refraction by Plates with Plane and Parallel Surfaces........ DE Be PES er Pee Pry rr eee Ce piety eee es: Refraction by a Spherical Surface ............cccceccecceces i CAM CORO : 6k i cayewseuh ences wsiewbeeecscetanesan es STU TEPeER Cee CEE K Cvetenpeceen's

CHAPTER ITI THE OPTIC SYSTEM OF THE EYE ce Rmeents OF tO BGG occ duaseest ccareetstededucivseuse Optic System of the Hye ...siccsccccccccsccccecucs vidtahiens re GF. 100 ystem. ..ccccrcacerenesbetheestbecdastedtewe Point of Fixation. Visual Line................... Gvtdvaeeds RUMI D. wasccerermeieimeits sareeinesd bie deae ed ueee ss MERE AMEE Cc ccccacnabesarderesescoesescecdaceeueteuauis EEE Snavaccecsavesscddocrasedrerdedts sctoude twesses

22. 23. 24, 25. 26.

9° wOe

36. 37. 38.

40. 41.

42. 43. 44,

45,

46. 47. 48.

Chapter III The False Images Of The Eye

NGENGY EI RGUIDTER: 245 gic ais do bi 3.0 djs bwe es inser jad sasne sie a raat 47 The Images of Purkinje .........sscssscceccsscesessseosess 48 Manner of Observing the Images of Purkinje ............. ioe! ae False Images of the Second Order ........ceccsccecscccees . 54 Manner of Observing the Sixth Image ............ceeeeeeeee 54 Bibliography .......sccsssvscccevvccccccsccssscsccsecssess 56

Chapter IV

Principles of Ophthalmometry ...........ceeeccesccccscccees 57 Methods of Doubling 2... .cccacscssccsccrccssceseecescesse 59 The Ophthalmometer of Javal and Schiotz ............see000- 61 Results of the Measurement of the Cornea ...........eeeeeeee 66 Measurement of the Angle @ ........scceccccccescescccnsces 77 Determination of the Position of the Internal Surfaces........ 80 Determination of the Centers of the Internal Surfaces.......... 83 Direct ‘Determination of the Badw 6 oss 500s sa00e nen oanes 84 General” Remarks’ hc cs ceca isc es cs00s 00s 0d 5550 ORR ee 85 Bibliography .....0.cccscscsescsesescesverecs +60 on Wee wie ieaw 87

Chapter V

CIRCLES OF DIFFUSION re eer rere re eer rrr rr. rrr 88 Line Of Bight. viscsiacassecesasdes wee seensdevess suse cee 89 ACCOMMODATION 3)6.4.54016.5'c,4108'5 sets Hae 3 696 56 0 eee ee 89 Experiment of Czermack, Scheiner and Mile .............-0+ 90 The Optometer of Thomas Young ...........eeeeeeeeceeeeecs 91 Effects of the Stenopaic Opening ...........cessesecvesesss 92 BipNograpay sic. cs sk cs wis cstuedcns estas 5 es eee 94 CHAPTER VI

General Remarks .......... wee oR Se RSS Die Peas siete 95 General Remarks on Ametropia .........ccceccescsccecsceves 97 Optometers, oo ccccceccisncnntaqns edie ebess s5555ke hs see 100 BEY OPIG. J4:5 is. 5,0;:8,5,0.0; 9,0 6.0.0, 5.4/8, 6:5,4, 094,40 ee ol os: Choice of Spectacles ........cccccccsssovececccccdesseseans 104 Treatment of Myopia .........cceccsscevccccccseccccsccceens 106 Hypermetropia ..cecsccccosvcasessccsctessasebosseussskeuer 109 rT) 7) or erie rire eee hen tt CEE eo irk 111 BibliogTaphy oo.o0.6.0.5.0.0.5.510.0,6 sBiseesecrcevdscaess stew ORE e aD 113

50. 51. 52. 53.

Chapter VII

Optio Principled «2... cece cscccccccsenececceccecnesecscs 114 Phenomena Dependent on the Spherical Aberration of Lenses... 115 Aberration of the Human Eye. Experiments of Volkmann..... 120 Merporiments of Thomas Young 22.660 ccccccccccccccseeas eves 131 UMIOMTODNY occa kchac de danes ccdcercstssvicvcescwanensncs 130

Chapter VIII

ONOE WUUMOIOG ons ince eck cee cdeeetncceeceeenceeHoeedds 131 Chromatic Aberration of the Bye .....ccccssscsceccccceccecs 133 UTNE GE WROTE ooo ices dence ccc ccewndsnteceens 134 MD bre aa ok a Ua, 30.9 ia a a kia Mio ala eig # acura'g Rie aidco pia mcare lately 135 Phenomena of Dispersion, the Pupil being Partly Covered...... 136 Correction of Chromatic Aberration ...........cceceessceces 137 UNI 2s is odd wide cece tnves Coad evden eee nsces Raeweeead's 137 CHAPTER Ix

Optie Principles, Astigmatism Produced by the Form of the

OD Seve brc une Kdavddeede averse ces secharseweehees 138 Dafecia Of the TMA 5... cc cccsccsccecsccccssievessevesees 141 Astigmatic Surfaces ......ccccccccccccccccceccccccccsescess 142 Astigmatism by Incidence ...........scccccccccccecccsscons 143 Astigmatism of the Human Eye. Historical ................+. 145 Pipehetogic Astigmate. 2 ico cciccccccccecsedecececctcevcas 146 Demeel Asti Matiame ones ccc ccc ccccccercvdcncccevccssoces 147 Measurement of the Corneal Astigmatism ...........+...2000. 147 Meegumee Cermenl Agtigminieme |. 2... c ccc cc cc ccccccscecceacs 149 Relations between Ophthalmometrie and Subjective Astigmatisms 150 PMRIGmAtIS AGCOMIMOGREIOE 2.266 ccc ce ccc cidedeesensaceesens 155 Post-Operative Astigmatiom ........ccscscccccccscescccccccs 156 NRDMMR Sau Seek ce cserecdecsercoccaedcesececeetonanene 157 eee Of Antigumtiee 65sec i ccccctccsnsseevveuseees 158 Examination of Astigmatic Patients .............cceceeceees 159 PURO ices ccc evadeve cures eteeeteresscecbeeedecacese 163

vii

79. 80. 81. 82.

83. 84. 85. 86. 87.

88. 89. 90. 91. 92. 93.

94. 95. 96. 97.

Chapter X Irregular Astigmatism

General Remarks ....000cccccccccccccncssessesecvvesecssses 164 Examination of the Eye with a Luminous Point ...........+.+. 165 Different Forms of Irregular Astigmatism...............0++4: 166 Rules for Analyzing the Figures of the Luminous Point....... 171 Bibliography ........cccescccsccccccccescccccccscessecsece 175

Chapter XI

Manner of Observing Entoptic Phenomena ..........+.++++e++ 176 Analysis of Entoptic Phenomena ...........+-seeeeeeeereees 180 Entoptic Observation of the Vessels of the Retina ............ 183 Other Entoptic Phenomena .......... ee ceeeceeccscceceeeces 186 Bibliography 2... .00.ccccvedcccsscsssscesteveesscoussessas 191

Chapter XII Accomodation

Measurement of the Amplitude of Accommodation ........... 192 Mechanism of Accommodation (Historical, A) ..........+e06- 195 Mechanism of Accommodation (Historical, B) ..............- 201 Personal Experiments 2... ccc ccec ee vcccceccsanesccesneseuus 206 The Author’s Theory of Accommodation ...........seeeeeeeee 220 Bibliography ....s.c.ccsccsscssnsccvcccsccccsscccccsssenses 228

CHAPTER XII

Methods of Illuminating the Fundus of the Eye...........++-- 229 Examination by the Erect Image ...........+eeeeeeseeeeeece 232 Examination by the Erect Image. Observations ...........+-- 237 Examination by the Inverted Image ..........eeeeeeeeeeeeees 241 Ophthalmoscopie Examination of the Refracting Media ........ 245 Gkiascopy ..... ses e cece cece eee ec cece cece ssereccesseeeees .. 246 Bibliography .......e: eee ee eee reece eeeees Aeeeey errr ety 253

Chapter XIV

General Remarks .....cc cece ssc cccnsceccecseccncescceasnsns 254 Action of Mydriaties and of Myotics ........+++eeeeeeeeeeee 255 Movements of the Pupil ..........cccceeccec es cecenceeccees 256 Advantage of the Position of the Pupil near the Nodal Point... 259 Bibliography ....... see cece eee e cece eeeeees eee eee eee ee ees 265

98. 99.

100. 101. 102.

103. 104, 105. 106.

114, 115.

Chapter XVII The Color Sense

PAL TRBTRBIES Soci ce ii ec cpewes dudewnevadecsentesacs 282 Phenomena of Contrast (Simultaneous) ...........see eee eeeee 287 WTINE TRO. io. in is ou cies fa bac he ecbek casewcececstecsecnenes 291 Phenomena Dependent on the Variation of the Brightness of Diy EN ss Stak cade catcle See ocala deswamene tet wes 293 Methods of Mixing the Colors .........+eseeeceeceeceeceenes 298 Results of the Mixtnres of Colors .......cseecsswctecsscseres 301 Abnormal Trichromasia. ...... 6s iu cscs cacisw cave sieceviewcese 315 Color Blindness or Daltonism (Dichromasia) .............+.+- 317 eMC TMCTAAMMESE «i. ox 6s 6:0) spe oe Ua Goncw addin aierd a(gs-d Ge GW aaa ie: se 324 Clinical Examination of the Color Sense .............2+eeeee- 324 Hypotheses on the Mechanism of Color Vision ................ 327 Bibliography .......cccvccceeeseccecssccsccccscccsssccseees 332

Chapter XVIII The Form Sense

Cemtral Viet) Acuity cocci cece ccccseeccesccaccenesenvaes 334 Peripheral Acuity .........0ccccecceccecseccsecvecsceees es’ Bibliography ......ccccccccccccessccsvesccccsesevenes rrr 345 ix

120. 121. 122. 123.

124, 125. 126.

127. 128. 129.

Chapter XIX

Centers and Axes of Rotation of the Hye .............eeeeeees 346 TSW MOL MMMEAT ESE eile niele vet's 66 aio sie slecele oN ogo olhi6\ a 6's > aS oleae 348 Experiments of Meissner. Apparently Vertical Meridian ...... 355 Ce Ey ee ner ae ee ees eee eee ee 358 Bibliography ........csecsecsecceees Cesc on eeccecvesessaceee 359

Chapter XX

Jerking Movements of the Byes ........ccecccccscececceceses 360 Relative Movements of the Two Eyes ...........eceeecscecees 360 Measurement of Comyergence ..........cescvcccccccccesccene 363 Relations between Accommodation and Convergence ........... 365 Pe Cs ne ero rrr Peres Se re ee Perr eoeee 365

Chapter XXI Projection Of Visual Impressions

Projection Outwards of Uniocular Vision ..............eeee0- 366 Projection of the, Visnal Wield .....0ss0s seddiiee cewetibween 366 Projection in Binocular Vision . oo sess csiesivessncs sevens 369 PTE Sg a eee eee eer free Petr cry ee 376

Chapter XXII

MONOCULAR PERCEPTION OF DEPTH ynaiinence Of ACCOMMODATION... 5). ae cscs wie edie bis s ow Senta wie 377 Indirect Judgment of Distance ........ccscccecnccverccccecs 377 intinenes,of ithe Parallax); .:c55:0'504-<. 4. aisvetensieletey ciara scsibipietens 380 IBHOGIADDY © 6c... ese cu ctee se ebenenaes seas s esh5 2 sane ies 381

130. 131, 132. 133.

Chapter XXIII Binocular Perception Of Depth

Influence of Convergence .......cccecccccccvccccccnceccecss The Stereoscope ........ cc ccccccccccccecccccccccecccccesees CT Be BPE eee rere eT eeRTE TEST Tere eee Werte OF. MG TRRUND oie iss 5 ce cede rccncawesssnn ds BERIORPADEY oo oc cece ce ccc ccc ccc secvesecertessseesess

CHAPTER XXV OPTIC ILLUSIONS SE SNE cd adees acess eeuNeeeeeheucusiuas Oueeoaseeee (ee

LIST OF ILLUSTRATIONS

FIG, PAGE 1. Luminous Source, Opaque Body, Shadow and Penumbra......... 1 2. Reflection on a Plame Mirror ........ccccrsencccceccceasence 3 3. Reflection on a Concave Mirror 2.1... ..cccscsccvcerccvencenes 4 4. Reflection on a Concave Mirror 20. oii cnc cannes cecccnaecwasee 5 GS. Reflection on a, Comvex Mirner occ case care dene vind sass cee geis ee | 6. Construction of the Utilized Part of a Mirror ................ 9 Dg MURAI hac hislcn & wads iat diode ah opadaltaerelns¥ Wig) e sie nis & elev iaisla wale Seapelie > 9 GS. Total Hofheotion 2... ..06. coc scwcctecavcwwecencensceneasenes 10 o.. (Pieme With, TEtal HEhechion: <.s'.% ie 4c sso ed a supsmlaeawee sielcaas 11

10. Refraction by a Plate with Plane Parallel Surfaces ........... 12 Oe EO 8 ee er irre) kee eee 12 12. Refraction by a Spherical Surface ...........cscecsecccesces 13 13. Refraction by a Spherical Surface ..........csceecscsscccccs 15 14. Refraction by a Parabolic Surface. .04 06 oii cid venieeseswcees 16 15. Construction of Image Formed by a Thin Lens ............... 18 16. Method of Measuring the Focal Distance of a Lens............ 21 17. Principal and Nodal Points; Anterior and Posterior Focus..... 23 18. Construction of the Image of an Object ...........2cceceences 24 19. Construction to Find the Second Principal Plane ............. 25 19.a. Construction of the Cardinal Points of Two Optic Systems..... 27 20. Construction to Find the Nodal Points of a Thick Lens ........ 28 in. See. mepecems Of the Tipe is o's. cei tints city cnbh dewgubaseeaed vs 33 22. Optic System of the Eye of an OX ........ceccccccccescesces 34 23. Images of Purkinje of the Eye of an Ox (Dead) ............. 35 24. Double Crystalline Images in a Case of False Lenticonus ...... 36 25.’ Diagram of the Crystalline Lens .....cssnccccccccccssocceses 36 26. Position of the Cardinal Points of the Human Eye ........... 39 27. Pupil of Entrance and Pupil of Exit ........ ai aiplekeal Sa aoe whale ei Dw 43 28. Reflections and Refractions by a Lens ...........0.eeeeeeeees 47 29. Manner in which a Luminous Ray is Divided in the Eye ....... 48 30. Position of the Seven Images in the Eye ...........-+eeeeeeee 49 31. Corneal Images of two Lamps Observed with the Ophthalmo- PRAOMStee oo a's vine vs aidivass bbe nw ideerinbrs évaswesscres 51 32. The Ophthalmophakometer .........ceceececcscccsscccececes 53 33. Illustration of the Principle of Doubling .................-4.-- 58 34. Doubling by the Two Halves of an Objective ..............+.-- 59 ee take Oh, ELOAONGZ, is.o wise sees ain a: wel wiehee Aglaia ei Viale ba orvease 60 36. Doubling by an Objective, a Central Vertical Band of which has WOME. FUCTIMI VOD: 5 a.p oo 5iwik'p dco ian ative Ra abe baal ee ives Winte asin 60 a) Bemee OF Wollagtonl ooo oo vised ctis oda bd dias eisde sade weawee 61

FIG, PAGE

38. Ophthalmometer of Javal and Schioetz ............ec eee eeeee 62 39. Images of the Mires Seen Doubled ..........cccscccavcvceses 63 40, Refraction by a Ooniedl Oormes si 5 ici Coin dee occ bs peceadeses 65 ai, Badli of Curvature of the OOrnee sisi ccc dvs eset ov ds twee ee 67 af, /Dingram-ot Corneal Retraction! 0. 7acic< scales oie bos 0/6 0/0 bo a1 abe 69 43. Forms of the Image of a White Square at Different Parts of

EO0 UOTBOR. 6 issv.u ns eGaV inane SHORE NRA VAs ves eset eee 71 44, Keratoscopic Images of an Astigmatic Cornea ................ 73 45. Keratoscopic Images of an Astigmatie Cornea ................ 74 46. Keratoscopic Images of a Case of Keratoconus ............... 75 46a. Keratoscopie Image of an Eye with a Large Angle a .......... 76 46b. Spot of Mariotte of an Eye with a Large Angle a ............. 76 47.. The Ophthalmoephnkomotior 1.6: 6 acide cde sce ck secs ceeences 2 i 48. The Images of Purkinje Observed with the Ophthalmophakometer 78 49. Position of the Images of Purkinje, the Lamps being Arranged

Werte y. iiss crea aleGiipaia tae wate kee woe bk po ss 0v Soh en ee 78 50. Position of the Images of Purkinje, the Lamps being Arranged

ERGOT UDHNN® (555 ini 'n pos inistaleinele'n'uie ORES ak Shae es a wEOS a> 79 51. Defect of Centering; Alignment of the Images Impossible...... 80 52. Determining the Position of an Internal Surface of the Eye.... 81 53. Determining the Position of an Internal Surface of the Eye.... 83 54. Calculation of the Size of the Circle of Diffusion.............. 88 oo.) mules O2. the - Optomoter-of Young’... 65. .c ide ee st ccwsbanss 90 56. Magnification by Means of the Stenopaic Opening ............ 93 57. Retinal Image in Myopia and Hypermetropia ................ 99 Ho eee rmempie (Ol. BAMHI tiisnck cases hoes els es 60100 Ses we ee Me 101 59. Size of Retinal Image when the Focus of the Lens Coincides with

the: Anterior ‘Focus 0f the bHyew..h is skkas levees oe eaeea se 101 60. Distribution of the Anomalies of Refraction ................. 103 61. Refraction of a Pencil of Parallel Rays by a Spherical Surface.. 114 Ge., Bpherical Aberration of 0 Lene ois 60U i Sec ee secs sseueane 116 63. Deformity of the Shadows of the Needles ...............0005- 118 Oe. mexperiment . of . Volkmiatiti. 43.9554. ies te da etc ee aya emt 120 65. Distribution of the Light of the Circle of Diffusion ........... 121 BGs AO ADOTTOSCOPG : is x) os chanel aise sas Wes UR ee eileen tere He etans 122 67. The Rules of the Optometer of Young .............sccesceees 122

68. The Appearance Assumed by the Line of the Optometer of Young 123

69. Deformity of the Shadows in an Eye with Strong Spherical Aber-

PAGIOM ace le RW te ewe eek lete Sila are Gall bic oN tees tere ere nee 70. Aberration Over-Corrected Towards the Borders .............- was J eperration. Over-Corrected: (A BOVe! : sus. Gus cave eaves sean 72. Aberration Over-Corrected Everywhere ...........e.sseceeeee 72a. Stadfeldt’s Instrument for Measuring Aberration of the Crystal-

94,

100. 101.

Phenomena of Dispersion ..........ceccececceccccceceessencs 136 Circles of Diffusion and Focal Lines of a Regularly Astigmatic

ee here ere Tre err ee ee eee rrs ree Tre 138 Foeal Lines of a Regularly Astigmatie System ............... 139 Construction of the Elliptical Diffusion Spot ................. 140 Su ecg vase h Moe Chak b ea thee hee kacasdver seek eeearewen 143 Focal Line of Lens Placed Obliquely ...............ccceceeee 144 Astigmatism by Incidence; Focal Lines ...............------ 144 Explanation of the Difference in Level (denivellation)* ........ 148 Keratoscopic Images of a Case of Keratoconus ............... 157 Forms Under which a Luminous Point is Seen by a Regular Eye 166 In Regular Astigmatism with Spherical Aberration ........... 167 Figures of a Luminous Point Obtained by Combining a Spheri-

eal with a Cylindrical Lens .........cccececeeccececcecs 168 Forms which a Luminous Point Presents to the Author’s Right

DO reer ey t revere Tere e eee eee Sear? eee 168 To an Eye with Double Obliquity ...........eceeceeecceeeees 169 Figures of the Left Eye of M. Rée ..........eeeceeececeeees 169 SE EE CMO Cis ta dend bcs cdancngsasecvrneewentaewaees 170 Irregular Bye (Diplopia) .......ccccccscccccccccccccesceccs aval Aberroscopic Phenomena .........-.ceccceccccccereseecscees 173 Diagram of Variations of Refraction in the Pupil ............. 173 Course of the Rays in the Author’s Right Eye ................ 174 Specks on the Anterior Surface of the Cornea ................ as Stria Produced by Winking. «02.0200 c2 dead cece dec ceieeeees 177 Prismatic Effect of the Layer of Tears ............cceeseeees 177 Speckled Appearance of the Entoptie Field Produced by Rubbing

WE COON ok adc dadcnctuchenenk na eheenV eee ets rncss 178 Star Figure of the Crystalline Lens ...........seeecceceeeees 178 Incipient Cataract Seen Entoptically ...........e eee ee eeeeees 179 The Hntoptoseope .......cccccccccccccccnccdseevesevicnsesess 180 Parallax of the Entoptic Phenomena ..............-.eseeeees 181 Determination of the Position of an Entoptic Object .......... 182 Entoptic Luminous Image Surrounded by a Shadow ........... 183 Entoptic Observation of the Vessels ...........2ceeceeceeees 184 Entoptic Observation of the Vessels .........0.cececccceccece 186 Wintoptie Phenomenon 3... icc ccc ccsteecncnrccacvesovecseune 190 Centripetal Movement of the Catoptric Image ................ 196 Putting tho Bye Under Water . 0.2... ccscccccsccenscnccccucss 202 Ciliary Muscle of Man .....:.ccccccccccccccsssteevesceveres 204 canary Part. of the Bye of a Cab. oiics fe i seus ee ee eee 205

Change of Aberroscopic Phenomena During Accommodation.... 206

*[ This a 83 does not quite illustrate the actual picture that we obtain by looking at the corneal images and L with the ophthalmometer. For with the Wallaston prism K is not seen any more, but instead of it we observe 7 at the place indicated in the figure, and K, at a distance,

K K, to the left of K in the direction o that omitted.

doubling of the prism. The same is the case with L,, only — te the right. But to avoid complication the two images K, and L, have been xV

123. 124, 325.

127. 128.

130. 131. 132. 133.

PAGE Appearance of the Luminous Point ..............ccceceeecece 207 Appesrance! or the Lnminots Pomt oe epee te ve es 208 Skiascopic Examination of Accommodation ............2-2000. 210 Reflection Images Of The Wye 23. ci ccw cise weer scree seeese 211 Reflection, Images Of the Wye... 0 ics. swe nevecvecseseseecwns 212 Refieetion Images of the Bye) .../.'s:.i0s. io sjs assess siaie vies vie awiserel 212 Deformity of the Corneal Image of a White Square in a Case

CERRO COMER E's chain's Bait die aamia Rib ais mim els orale Brew @louatene Nie 213 netreciion by a Parabolic Burfaee «oie osiisiics isaidewsabiwsas 214 Deformity of the Crystalline Surfaces During Accommodation... 215 Accommodative Phenomena of the Eye .................ee00e 216 Accommodative Phenomena of the Hye ...............eeeeee 217 Change of the Anterior Chamber During Accommodation....... 219 Reflection Images on the Anterior Surfaces of the Dead Crystal-

AML iL e Ai psol Siu leis Giese o saynte lk a TeSeeatel aire a ein'a: anata ie Crary s Saree mene 221 Crvetatiine Lana of the: OK 6. sci tiie sep aisisee nes ames eaten 223 Optic System of the Hye, of the Ox, 0.5 aici. nasties inseam ola wiles 224 Illumination of the Fundus by a Light for which the Eye is

A GCOMMO MALO: i\¢ Giese% 6m w:s510 Rie re Baste. oh wile neerarel eis Wikiiaietarass 229 Illumination of the Fundus by a Light for which the Eye is Not

A GOOVINGGATCG! 5:5) cs:5. dine oles eve Bios aie Me Ieebi ab dela mI nye Sic loeumieel Ns 230 Principle of the Ophthalmoscope of Helmholtz ................ 231 Magnification of the Fundus, both Patient and Observer being

TMIMSULODIG sais ws eis he ee Bice aie 6 ee we ee ee aOR ate 234 Line of Image of Papilla if the Fundus of Patient is Placed Free

AG Fc ee ama peared he 5 cin SR ky geist Ws Re ee Tae Gb Att 235 Magnification of Fundus if Patient is Myopic ................ 235 Construction of the Ophthalmoscopic Field .................. 236 Magnification by the Inverted Image in Emmetropia .......... 241

Influence of Refraction of the Examined, Eye on the Magnification if Focus of Lens Coincides with Anterior Focus of Eye 242 Influence of Refraction of the Examined Eye on the Magnification if Lens is Nearer to the Eye than in Fig. 133........ 243 Construction of the Ophthalmoscopic Field by the Inverted Image 244 Sainneopy. Plane Migvor 65 s\os\sis'5 4's s Mnine s Ap cd owns a tenses 247 NKIGBCOPYs | ‘CONCAVE | MATTOR Vk cisisie chats wieiwlaletarsih s.cGiWy viaieveystelale als 247 Boundaries of the Skiascopic Field .....6..ccscccccccvasecens 249 PEBEGEY, OL MAOTOY, 66g tec 4 eck ioe oie e wiaratere oheleis Grey > a) Ss 6s esia\e Ace noe le 250 PRGOPY OL GOTO civ ais ie je ols hahaa die hie Gian eine wip whale Si ue RL 250 ABpory Of the Paracentral Shadow sits 241. vies «sdiee cs es eareeiets 251 The Advantage of the Position of the Pupil Near the Nodal

MOINS cif as asc dN ace h Obes wena he Be Se REO OR RE Ns nena aisle 259

¥IG.

PAGE 143. Experiment of Helmholtz ..........+..-e.0 Wie Stare wet cine gale 260 144. Hyperbolic Chessboard of Helmholtz ..............cceeceeees 261 NS RENE OO es i ccacniad M8 BARA TUAW UO) duals GUNES och SkeeVasrnue 262 146. Image of a Window in the Artificial Hye .................... 263 1464. Section of the Retina of a Frog .......cccccccccccncecccseecs 268 Sees Teens OF Rota ys cc cwsdeca dso. ce diney s eh Sea 271 148. Curve Showing the Relation between the Light Sense and the TAT ENOE: oes cae sicardele deaiala? gece ae a were Oh ciaaene ets 273 mame. Pescsuesmeeent Of Foerster «6 osicecncodwawabids cus daevewewed sls 275 ee TUTTLE TORE TT Oe EL CRE Tee Tere 276 150a. Dise of Helmholtz and Dise of Benham ...................... 277 151. Spectrum of Refraction; Spectrum of Diffraction ............ 283 308. Table of Calorn- efter Nowtom cn inca cede ie isis Sen cstaeeweeds 285 aGn. Mieperiment of Hagona Being «ook oc icc cscecsdee ckeiide eek s 288 154. Experiment with Colored Shadows ..............ceceeceeees 289 CY PRICING RMMMONER 255 fora raids aa qie'e w c.geitie ae Me She aw me aareGE © ASE Sela 290 156. Curves of Parinaud to Show the Threshold for Different Rays of Re NEU wei Wec aed cans dveeRar sess eevee ee Gas wed 296 re eGR ErE OF MAMWOUE (tu ilia si echie didtaace ers ohie heleie aule oats & asta 299 158. Mixture of Colors by Means of a Glass Plate ................. 300 me Chenin OF COlrS aiter NOWtOR ccuicic.decccanceee eres veleis veces 303 Se. eee, ne OE SRM WOEE sci Ox d's dex WS a eR Siem A Siw alse wa Sie 304 bees 1G Nee EER OEE UNEWONL. o25 5's ics cic. bale erelatelha x ecman ats ae mernees 305 ee CEC EVER: OF DEAT WEIL \a)0 sic ic's s cutee + diemsehG seneaieg cuales aes 306 Ge mein Ramle OF MIASWOIL.

Oooo cpacc cs wes tec dade si tanewien aa 308 eeet nO aietiee Re UEDEG” QE FRCUERTIONGE. o/h c's a siciels po vaweee sacs Or Cece eae se 313 eee OME EG OE” ATR WOIE oo; ue ciacia t's clelga wa seme marsala’ puja ek cote 319 Geen Color Curves Of a BDichromatio .30)0). cc. ccescccsaecedeawus 321 ie Omron rape Of & PiGhromatie «66's scicecls vssievisccemed ee wanes 321 moe. Cnroniatoptomoeter Of Chibrot: <x oss... <..cci06 vic eisvi os iv 8 oelslern eee 326 Ger oy ee ICREMCING. COE EROOEG <6) o\0/c.ci os <3 vivialain waslaivie seus daewoo Sake Re 335 170. Measurement of the Visual Acuity by a Grating .............. 335 171. Measurement of the Visual Acuity by a Grating ............. 335 172. Experiment of Hooke, the Optics of the Eye being Defective.... 336 Se eh REEL CHOIR: hired ob ainda vice aceune uads eeeead be awe 343 Biase e PeeONOM OF. ERORICN ° 0%, 5)6.cig'<o edrele Uelewvisnis els elcc da agiee ears 344 175. Determination of the Center of Rotation of the Hye .......... 347 176. The Two Axes of Rotation Lying in the Horizontal Plane...... 347 177. Demonstration of the Law of Listing .............cecceceeces 350 178. Demonstration of the Law of Listing ..................eceeee 351 179. Demonstration of the Law of Listing ...............eececeeee 352 emer PREBOEy OG V OUMMANITL 5.5. 55a <a !o: o alscaln: oa sroisiarere ema ereceieleltielere a wa e'e 356 181. Modification of the Experiment of Meissner ................. 357 xvii

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Illustration of the Meter Angle ........seseceeeeeeeeeceeees 364 Explanation of Binocular Physiologic Diplopia ............-- 370 Experiment to Find the Center of Projection ........-..++++: 373 Horopter of Johannes Muller ..........cceesccccsscceecvveee 374 Apparent Form of the Sky ..........sseeccccccserccceeerece 379 Influence of Parallax for Stereoscopic Vision ...........+.+0+5 380 Principle of Stereoscopic Images ...........eeeeeesceeveeees 383 Stereoscope of Wheatstone ......... cee eee cee cree cece reesens 385 Pseudoscope of Wheatstone .........c.eceeeceececcceccecces 386 Telestereoscope of Helmholtz ......... cee ceec eee ceeceeeeees 387 Binocular Ophthalmoscope ........0. cee ceecceccceccsscceecs 388 Antagonism of the Visual Fields ...........cccceccccscvsscns 390 Suppression of one of the Images in Stereoscopic Vision ....... 394

195 to 201. Optic Illusions.

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Chapter I

1. Optic Properties of Bodies.—Bodies are of three kinds; transparent bodies, through which we can see objects, translucent bodies such as ground glass, through which we perceive light, but cannot distinguish form, and opaque bodies.—No body is absolutely transparent. Pure water is transparent, but very little light will pass through a great thickness of water—On the contrary very thin layers of opaque substances are more or less translucent, as all know who have examined microscopic preparations.

Fig. 1.—A, luminous source; B, opaque body; C, shadow; D, penumbra.

2. Rectilinear Propagation of Light.—In a homogeneous medium light is propagated along straight lines which are called luminous rays.

SHADOWS.—When rays emanating from a luminous point fall upon an opaque body there is produced behind the latter a shadow “which is conical in shape. We can construct the form of this shadow by drawing straight lines joining the different points of I the border of the body with the luminous point. If, instead of a point, the source is a luminous surface the shadow is surrounded by a penumbra, the intensity of which diminishes more and more towards the periphery. An observer placed in the shadow C could not see any point of the luminous surface; placed in the penumbra D he would see a part of that surface, greater in proportion as he approaches the border.

Imaces PropucED By A SMALL APERTURE.—Rays passing through a small aperture into a dark room form on a screen an inverted image of exterior objects. By diminishing the aperture the image gains in distinctness, but loses in luminosity. Photographs may be taken in this way.

8. Reflection and Absorption—Rays which strike the surface of an opaque object are partly absorbed and partly reflected. If the surface is not polished the rays are reflected in a diffuse manner: each point of the surface sends back light in all directions. It is through the agency of this irregularly reflected light that objects are visible, and the fact that they are visible, whatever may be the position of the observer, provided the rays are not intercepted, proves conclusively that any point whatever of the surface sends rays in all directions.

4. Regular Reflection—The more polished the surface the less diffuse is the reflection. Thus the surface of a highly polished mirror is but slightly visible. Polished surfaces reflect rays regularly following a law which was known from remote ages, viz., that the reflected ray is in the same plane with the incident ray and the normal to the point of incidence, and that both rays form equal angles with the normal, which is expressed by saying that the angle of incidence and the angle of reflection are equal.

The effect of this reflection is to produce images of external objects. The image of a point is the place where the rays which emanated from that point meet again after reflection or refraction. In order that the image may be perfect, all the rays employed should meet in a point. Generally this condition is not quite fulfilled, there being more or less pronounced aberrations.

—A point and the image of this point we designate as conjugate points—An image is real when the rays proceeding from a point meet again in a point; it is virtual when it is formed not by the reunion of the rays themselves, but of their prolongations.—A\ real image can be received on a screen; a virtual image cannot, but it is visible to the eye which is in the path of the rays because the optic system of the eye forms a real image of it on the retina, exactly as if the virtual image was an object.

5. Plane Mirrors. Construction of the Image.—Let fall from a point A (fig. 2) of the object a perpendicular AB on the surface, DE, of the mirror, and mark on its prolongation a point

A tae eeedee =

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Fig. 2.—Reflection on a plane mirror. A, the object; A’, its image; DE, the mirror; AC, incident ray; CF, reflected ray.

A’ so that AB is equal to A’B. A’ is the image of A, for since AB=—A’B, the two angles @ are equal, and consequently also the two angles i, each of which is equal go°°— *% The image formed by a plane mirror is virtual, erect and equal in size to the object.

To tell whether a mirror is true place the eye near the surface by way of observing images under as great an incidence as possible. If the mirror is not true the images of external objects are deformed. One can also notice these deformities very distinctly by placing oneself quite a distance in front of the mirror and observing the images of distant objects.

6. Concave Spherical Mirrors——The middle of the spherical surface is called the apex, a straight line passing through the center and the apex is the axis, and the angular measurement of the mirror is the aperture. In order that images may be true the aperture must be small (8 to 9 degrees). The principal focus of the mirror is the place where incident rays parallel to the axis meet after reflection. The principal focal distance is the distance of the principal focus from the mirror.

In ALL Optic PHENOMENA THE COURSE OF THE Rays Is RE- VERSIBLE.—If in figure 2, the ray AC is reflected along CF, an incident ray along FC is reflected along CA.—It follows that rays coming from the principal focus of a concave mirror must be parallel after reflection.

The principal focus of a plane mirror is at infinity, because incident parallel rays are still parallel after reflection.

The principal focus of a concave mirror is situated half way between the apex and center. We have, indeed i=i (fig. 3), since the angles of incidence and reflection are equal, and i—BC® because the incident ray is parallel to the axis. It follows that C®