Optic Tract Syndrome Neuro-ophthalmologic Considerations Steven A. Newman, MD, Neil R. Miller, MD \s=b\ A review of the case histories of ten patients with optic tract lesions, an uncommon clinical entity, showed the primary characteristic to be a homonymous visual field defect that may be complete or incomplete. When the defect is incomplete, there is relative incongruity. When it is complete, there is an associated contralateral relative afferent pupillary defect. Visual acuity and color vision are preserved, unless there is bilateral involvement or anterior extension to involve the optic nerve or chiasm. When of sufficient duration, the contralateral fundus demonstrates band or "bow tie" atrophy of the disc and nerve fiber layer. (Arch 1250) Ophthalmol 1983;101:1241- visual field defects "LTomonymous * -* from optic tract lesions are rare,1-2 but are becoming increasingly recog¬ nized.3-4 Certain features of optic tract involvement appear to allow defini¬ tive diagnosis by virtue of the specific anatomy involved. We present our experience with ten patients having lesions involving the optic tracts. REPORT OF CASES Case 1.—A 9-year-old girl experienced the sudden onset of severe headache and vomiting with transient, horizontal diplo- pia. During the next several weeks, her headaches increased in frequency and severity. Visual acuity at the time of admission to The Johns Hopkins Hospital, Baltimore, was 20/15 OD and 20/20 OS. Color vision was not tested. Visual fields were full, with bilateral enlargement of the blind spots. Pupils were equal and normally reactive. There was no afferent defect. Ophthalmoscopic examination re¬ vealed bilateral papilledema. A computed tomographic (CT) scan revealed a cystic suprasellar mass. A right frontal craniotomy was per¬ formed, at which time a large spongioblastoma was found to be adherent to the hypothalamus, displacing the chiasm to the left. The tumor was partially resected, and the patient received postoperative radiotherapy (5,000 rad). Six months later, the patient was readmitted with recurrent headaches. Visual acuity and color vision remained normal; however, visual field testing revealed an incomplete, incongru¬ ous, left homonymous hemianopia (Fig 1). Pupils were equal and normally reactive. There was no afferent defect. The optic discs were normal. Neuroradiologic evalu¬ ation demonstrated severe hydrocephalus, and the patient was treated with bilateral ventriculoperitoneal shunts. During the next five months, the patient's visual acu¬ ity and color vision remained normal; how¬ ever, the left homonymous hemianopia progressed until it became complete (Fig 2). During this period a left afferent pupil¬ lary defect became evident, and ophthal¬ moscopy revealed hemianopic atrophy (Fig 3). Accepted for publication Aug 30, 1982. From the Neuro-ophthalmologic Unit, The Wilmer Ophthalmological Institute, The Johns Hopkins Hospital, Baltimore. Reprint requests to the Neuro-ophthalmological Unit, The Wilmer Ophthalmological Institute, The Johns Hopkins Hospital, 601 N Wolfe St, Baltimore, MD 21205 (Dr Miller). In this child, despite retention of normal visual acuity and color vision, gradual progression of a left homony¬ mous hemianopia was associated with the appearance of an ipsilateral (con¬ tralateral to the lesion) afferent pupillary defect. This finding suggests Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/07/2015 that an afferent pupillary defect is not seen in optic tract lesions until there is substantial asymmetry in the degree of visual field loss between the two eyes. Case 2.—A 12-year-old boy was first examined in March 1977, suffering from progressive, intractable, left-sided, grand mal, and psychomotor seizures. Visual acu¬ ity was 20/20, color vision was normal, and visual fields were completely full. Pupils were normally reactive to light. There was no afferent defect. Optic discs and nerve fiber layer were normal. Two and a half years later, the patient underwent a right hemispherectomy with removal of subcor¬ tical material and sectioning of the right optic tract. Postoperatively the patient's seizures resolved, although he had a resid¬ ual left hemiparesis. When he was reexamined six months postoperatively, his visual acuity and color vision remained normal. Visual fields demonstrated a complete left homonymous hemianopia (Fig 4). Pupils were equal; however, there was a marked, relative left afferent defect. Ophthalmo¬ scopic examination revealed superior and inferior arcuate nerve fiber layer defects with diffuse pallor of the optic disc on the right. The left optic disc showed band atrophy with generalized loss of fibers from ganglion cells nasal to the fovea. Surgical interruption of the optic tract produced a complete homony¬ mous hemianopia and a classic pat¬ tern of hemianopic, retrograde nerve fiber layer degeneration. This condi¬ tion was associated with the develop¬ ment of an afferent pupillary defect contralateral to the site of the surgi¬ cal lesion despite the continued pres¬ ence of normal visual acuity and color vision. Case 3.—A 17-year-old boy was referred Initial visual fields in patient 1. There is an incomplete, incongruous, left homonymous hemianopia. Fig 1. — Fig 2.—Visual fields in patient 1 five months after initial examination. There is now a complete, left homonymous hemianopia. to the Neuro-ophthalmologic Unit with a four-month history of progressive leftsided numbness following a viral illness. This condition was associated with mild weakness of the left side. Two months later, the patient experienced increasing incoordination, stiffness, and dysarthria. He also noted difficulty seeing to the left side. Neurologic examination on admission to the hospital revealed a spastic left hemiparesis, dysarthria, and left hemihypesthesia. Visual acuity was 20/25 OU, and color vision was normal. There was a virtu¬ ally complete left homonymous hemiano¬ pia (Fig 5). Pupils were equal, but there was a marked left afferent pupillary defect. Convergence was poor, and there were bilateral, mild, horizontal gaze pareses with saccadic dysmetria, especially with the patient looking to the left. Oph¬ thalmoscopic findings were normal. Sero¬ logie tests for connective tissue disease and syphilis were negative, but there were sev¬ eral oligoclonal bands seen on a specimen of CSF. The patient was believed to have demyelinating disease. In this patient, multifocal demye¬ linating white-matter plaques were believed to have included right optic tract involvement. Although the patient's fundi were believed to be normal, the presence of a complete homonymous hemianopia with an ipsilateral (contralateral to the lesion) afferent defect make a diagno¬ sis of an optic tract syndrome inescap¬ able. Because the subjective field defect preceded the evaluation by approximately six weeks, it is possible that retrograde degenerative changes had not yet occurred. Case 4.—A 22-year-old woman experi- Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/07/2015 enced transient episodes of left-sided numbness at 8 and 10 years of age. At the age of 22, she experienced the sudden onset of a left hemiparesis and hemihypesthesia. A CT scan demonstrated a large vascular mass in the region of the right optic tract, and an arteriogram demonstrated an extensive arteriovenous malformation in the right ambient cistern. On initial neuroophthalmologic examination, the patient's visual acuity was 20/20 OU, and color vision was normal. There was a complete left homonymous hemianopia, except for a small island of vision in the left hemifield of the left eye (Fig 6). Pupils were equal, but there was a definite left afferent pupil¬ lary defect. Ophthalmoscopy showed clas¬ sic hemianopic nerve fiber layer and optic atrophy. The patient underwent craniotoray and complete removal of the arteriove¬ nous malformation. Postoperatively she continued to have a left hemiparesis and complete left homonymous hemianopia. Fig 3.—Ocular fundi in patient 1 show hemianopic optic atrophy corresponding to complete, left homonymous hemianopia seen in Fig 2. Fig 4.—Visual fields in patient 2. There is complete, left homonymous hemianopia. In this patient, a portion of the arteriovenous malformation was fed directly through branches of the ante¬ rior choroidal artery. It is likely that this patient's optic tract syndrome was vascular in nature. 29-year-old right-handed began to have generalized seizures involving the right hand at the age of 7. At the age of 26, she experienced psychomotor seizures consisting in staring spells and Case 5.—A woman automatisms. An EEC demonstrated intermittent sharp waves that were more pronounced over the left temporal region. A brain scan was normal, as was a cerebral arteriogram. A pneumoencephalogram demonstrated some asymmetry of the left temporal horn. A neuro-ophthalmologic examination, performed one year later, revealed normal visual acuity and color vision. There was an incomplete, right homonymous hemianopia that was denser in the lower portion (Fig 7). No afferent pupillary defect could be demonstrated. Ophthalmoscopy revealed nerve fiber layer dropout in both eyes, with "band" atrophy of the right optic disc. Subsequently a neurogenic bladder and cerebellar symp¬ toms developed. Serologie studies and lum¬ bar puncture were unrevealing. Although the etiology of this patient's neurologic symptoms and signs remains unclear, the presence of nerve fiber layer dropout and hemia¬ nopic optic atrophy suggests the diag¬ nosis of a left tract lesion. Noteworthy Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/07/2015 is the absence of an afferent pupillary defect in the setting of an incomplete homonymous hemianopia (see also case 6). Case 6.—A 33-year-old man was referred to The Johns Hopkins Hospital in Septem¬ ber 1980, with a complaint of increasing headache and a sensation of "darkness" on the right side of the visual field. Results of a neurologic examination were normal. Visual acuity was 20/20 OU, and color vision was normal. Visual fields showed an incomplete, incongruous, right homony¬ mous hemianopia that was scotomatous in the right eye (Fig 8). Pupils were equal and normally reactive. There was no afferent defect. Ophthalmoscopic findings were normal. A CT scan demonstrated a left, Fig 5.—Visual fields in patient 3. There is a virtually complete, left homonymous hemianopia. Fig 6.—Visual fields in patient 4. There is complete, left homonymous hemianopia except for small island of field in inferior left field of left eye. cystic parasellar mass. At craniotomy, a cystic craniopharyngioma was found to be elevating and compressing the left optic tract. The lesion was incised and drained but could not be completely removed. Post¬ operatively the patient's visual acuity and color vision remained normal, and there was complete resolution of the visual field defect (Fig 9). The fundi remained nor¬ mal. This partial, left optic tract lesion produced an incongruous, homony¬ mous hemianopia with preservation of acuity and color vision. Decompres¬ sion of the tract produced rapid reso¬ lution of the field defect. This incom¬ plete syndrome was unassociated with an afferent pupillary defect. Case 7.—A 35-year-old man was first examined after he experienced diplopia associated with a severe headache. A com¬ plete neuroradiologic examination demon- strated a large arteriovenous malforma¬ tion in the ambient cistern. At the time of initial examination, the patient's visual acuity was 20/20 OU, color vision was normal, visual fields were full, and the fundi were normal. Pupils were equal and normally reactive. There was no afferent defect. Ocular motility testing demon¬ strated a mild, left, fourth nerve paresis. During the next four years, the patient's diplopia recovered; however, he experi¬ enced several episodes of subarachnoid hemorrhage, and it was elected to attempt removal of the malformation. Postopera¬ tively the patient had a mild dysphasia and loss of the right visual field. When he was examined ten days after surgery, the patient's visual acuity remained 20/20 OU, and color vision was normal; however, there was a complete right homonymous hemianopia (Fig 10). Pupils were equal, but there was a moderate right afferent pupillary defect. Ophthalmoscopic results were normal. Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/07/2015 This patient experienced a complete left optic tract syndrome after remov¬ al of an arteriovenous malformation that involved branches of the anterior choroidal artery. As in case 4, this patient's optic tract syndrome was undoubtedly vascular in nature. Case 8.—A 50-year-old right-handed suffered a grand mal seizure in 1978. Neuroradiologic examination demon¬ strated a right temporoparietal mass. A woman right temporal lobectomy was performed, and a grade 2 astrocytoma was disclosed; the patient subsequently received 4,000 rad to the right temporoparietal region. Imme¬ diately postoperatively the patient had a left hemiparesis and complained of diffi¬ culty with vision to the left side. Neuroophthalmologic examination performed two months postoperatively demonstrated a visual acuity of 20/20 OU and normal color vision. There was a complete left Fig 7.—Visual fields in patient 5. There is incomplete, right homonymous hemianopia, denser below. Fig 8. Preoperative visual fields in patient 6. There is incomplete, right homonymous hemianopia that is densely scotomatous in right eye. — homonymous hemianopia (Fig 11). Pupils equal, but there was a marked left afferent pupillary defect. Optokinetic test¬ ing demonstrated symmetric, normal responses to horizontal stimuli. Ophthal¬ moscopy revealed hemianopic nerve fiber layer and optic atrophy. were Although the patient's tumor undoubtedly involved the optic radia¬ tion, the finding of a contralateral afferent pupillary defect and hemia¬ nopic atrophy suggests that either the tumor extended to involve the right optic tract or the right optic tract was damaged at the time of surgery. Case 9.—A 55-year-old man was ad¬ mitted to the hospital with a two-year history of personality change and one month of difficulty seeing to the right side. Neuroradiologic evaluation, including CT scan and cerebral arteriography, revealed deep, left-sided mass involving the tem¬ poral and parietal lobes. The patient had normal neurologic findings, except for some degree of confusion and disorienta¬ tion. Visual acuity and color vision were normal. There was a complete right hom¬ onymous hemianopia (Fig 12). Pupils were equal, and there was a mild right afferent defect. Optokinetic testing demonstrated an asymmetric response, with saccades to the right being markedly decreased. Oph¬ thalmoscopy showed no abnormality. A left craniotomy was performed; a grade 3 astrocytoma was encountered and subtotally removed. The anterior 5 cm of the left temporal lobe was also removed. Postoperatively, the patient was treated with tapering doses of systemic decadron and radiotherapy (5,100 rad). Three months later the patient was reexamined. Visual acuity and color vision a remained normal. Visual fields showed appreciable improvement, with an Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/07/2015 ex- tremely incongruous, right homonymous hemianopia that was localized to the supe¬ rior quadrant in the right eye (Fig 13). Pupillary reactions were normal, and the afferent pupillary defect that had previ¬ ously been noted had now disappeared. Ophthalmoscopic results remained nor¬ mal. It is likely that this patient's optic tract syndrome occurred from either direct tomor compression of the left optic tract or secondary edema involv¬ ing the tract. Decompression and radiotherapy subsequently restored tract function. As the patient's visual field improved, his afferent pupillary defect disappeared, while visual acu¬ ity and color vision remained unchanged and normal. The residual visual field defect probably represents damage to the optic radiation in the Fig 9.—Visual fields in patient 6 two weeks after craniotomy with incision and drainage of cystic craniopharyngioma. Visual fields have returned to normal. Fig 10.—Visual fields in patient 7. There is complete, right homonymous hemianopia. left temporal lobe, thus explaining the continued lack of optic atrophy. Case 10.—A 58-year-old man noted pro¬ gressive loss of visual acuity in his right eye. Visual acuity OS was 20/600 and he was unable to identify any of the pseudoisochromatic plates. Visual acuity ÒD was 20/20 and color vision was normal. Visual fields demonstrated an incongruous, right homonymous hemianopia that was denser in the lower portion of the left eye (Fig 14). Pupils were equal, but there was a marked right afferent defect. Ophthalmoscopy re¬ vealed hemianopic atrophy, and a CT scan revealed an enhancing, suprasellar lesion. A frontotemporal craniotomy was per¬ formed, and a large meningioma, presum¬ ably arising from the planum sphenoidale, was identified. It compressed the right optic nerve and chiasm, and extended pos¬ teriorly to compress the left optic tract. The patient was not examined postopera¬ tively. In this patient, a right homonymous hemianopia associated with hemia¬ nopic optic atrophy indicated a left optic tract lesion; however, loss of visual acuity and color vision contralateral to the lesion suggested involve¬ ment of the contralateral optic nerve. This phenomenon was demonstrated at the time of surgery. Parasellar masses often give a combined picture of nerve, chiasm, and tract defects. RESULTS All patients in this series were examined by one of us (N.R.M.). Visual acuity testing was performed with standard Snellen's letters at dis- Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/07/2015 tance and Jaeger's cards at near. The results were recorded as best cor¬ rected if the acuity was less than 20/25. Color vision screening was per¬ formed using the Hardy-Rand-Rittler pseudoisochromatic plates. Visual field testing included confrontation technique, Bjerrum's (tangent) screen using both white and red targets, and kinetic perimetry with Goldmann's perimeter. Pupillary reactions were evaluated with an indirect ophthal¬ moscope as a light source. Ophthal¬ moscopy was performed with both direct and indirect ophthalmoscopes, and both color and red-free photo¬ graphs were obtained for most patients. The results of our examina¬ tions are seen in the Table and Figs 1 through 4. Fig 11.—Visual fields in patient 8. There is complete, left homonymous hemianopia. Fig 12.—Initial visual fields in patient 9. There is complete, right homonymous hemianopia. There were six men and four women in our series. The mean age at diagno¬ sis was 33 years (range, 9 to 58 years). All patients underwent CT scanning and cerebral angiography. Seven patients had lumbar puncture with CSF analysis. Optic tract abnormali¬ ties involved the right side in five cases and the left side in five cases. Eight of the ten patients ultimately underwent craniotomy with visualiza¬ tion of the optic tract abnormalities in all cases. Five patients had an underlying neoplasm, although in one of these patients (case 8), a subsequent com¬ plete tract lesion was believed to have been surgically induced. Two patients had tract lesions that were clearly surgically induced. In one patient (case 7), removal of an arteriovenous malformation resulted in a complete homonymous hemianopia. In a second patient (case 2), a hemispherectomy was performed for intractable sei¬ zures. Of the remaining three patients, one had an arteriovenous malformation, a second had demyelinating disease, and in a third patient the origin of the optic tract syndrome remains unknown. Six patients complained of hemia¬ nopic visual field difficulties; only one patient complained of decreased vision. Visual acuity and color vision were completely normal in all but one patient. When first examined, six patients had complete homonymous hemianopias and four patients had incomplete, incongruous hemianopias. In one of the patients (case 9), an initially complete defect partially resolved; in a second patient (case 6), an incomplete hemianopia completely Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/07/2015 resolved; and in the third patient (case 1), an incomplete defect gradual¬ ly progressed to become complete. A relative afferent pupillary defect present in eight of the patients at some stage of their disease. In one of these patients (case 9), the afferent defect subsequently resolved as the visual field defect improved. In anoth¬ er patient (case 1), the pupillary defect developed as the patient's visual field defect progressed. Both patients maintained normal visual acuity and color vision. None of the patients demonstrated anisocoria. Six of the patients demonstrated hemianopic retinal fiber and optic nerve atrophy with band or "bow tie" atrophy in the eye opposite the lesion. In addition to ophthalmologic signs, five patients had neurologic signs, was Fig 13.—Visual fields in patient 9 three months following subtotal resection of left temporal lobe astrocytoma and postoperative radiotherapy. There is incomplete, incongruous, right homonymous hemianopia that is localized to superior quadrant in right eye. Fig 14.—Visual fields in patient 10. There is incongruous, right homonymous hemianopia, denser below, in left eye. including seizures in three and hemi¬ paresis ipsilateral to the lesion in two. Two additional patients experienced hemiparesis after craniotomy, and one patient had a mild dysphasia. COMMENT Our experience with the optic tract syndrome suggests that several gen¬ eralizations may be made regarding various visual findings in such patients. Visual Acuity Cogan5 emphasized that lesions of the retrochiasmal visual system do not produce loss of visual acuity unless they are bilateral. Neverthe¬ less, two reports describing the oph¬ thalmic features of patients with optic tract lesions found a high preva¬ lence of monocular or binocular visual loss (82% ).3·4 Although this finding would seem to contradict Cogan's statements, Savino et al3 suggested that most of the patients in their series had extension to involve the chiasm or optic nerve, thereby result¬ ing in decreased visual acuity. The work of Frisen6 seems to support this contention. In fact, Frisen stated the following: Until evidence to the contrary is accumu¬ lated, it appears more rational to localize anterior visual pathway lesions with impaired acuity in one or both eyes to optic nerve(s) or the chiasm rather than to the optic tract. All of Frisén's patients with optic tract lesions reportedly had normal Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/07/2015 acuity. Of our patients, only one (case 10) had reduced central vision contralateral to the lesion. In this patient, a meningioma involved the optic nerve on one side and the optic chiasm and optic tract on the other side. Visual Field Defects It would seem that nonsurgical lesions involving the optic tract gen¬ erally produce incomplete homony¬ mous hemianopia.3'4·6 Savino et al described only one patient with a com¬ plete homonymous hemianopia, and Bender and Bodis-Wollner4 also reported that only one of their patients had a complete homonymous hemianopia that was traumatic in ori¬ gin. Bell and Thompson7 found only four of 24 patients with complete field Clinical Findings in Patients With Optic Tract Syndrome* Initial Examination Case/ Age, yr/Sex VA VF Pupil 1/9/F 20/20 OU 2/12/M 20/20 OU NL NL 3/17/M 20/25 OU 4/22/F 20/20 OU CLHH CLHH LAPD LAPD 5/29/F 6/33/M 20/20 OU IRHH NL NL Fundi PAP Final Examination Clinico¬ pathologic Findings Spongioblastoma VA VF 20/20 OU ILHH, CLHH Seizures 20/20 OU CLHH LAPD HA 20/20 OU CLHH LAPD HA Right OTS probably due to optic tract infarction 20/25 OU IRHH NL HA 20/20 OU NL Cause unknown No afferent pupillary defect with NL Multiple sclerosis HA AVM Cystic craniopharyngioma Pupil Fundi NL, LAPD HA Comment Development of LAPD with development of CLHH Right OTS after hemispherectomy scotomatous 7/35/M 20/20 OU NL NL NL AVM 20/20 OU CRHH RAPD NL hemianopia Complete OTS after Tempoparietal 20/20 OU CLHH LAPD HA Questionable extension of removal of AVM 8/50/F tumor to optic tract astrocytoma 9/55/M 20/20 OU CRHH RAPD NL Temporoparietal 20/20 OU IRHH astrocytoma 10/58/M 20/20 OD, 20/600 OS IRHH RAPD HA Meningioma NL NL surgical damage Disappearance of afferent pupillary defect with partial resolution of hemianopia Optic nerve, chiasm, and tract involved 'Abbreviations and symbols are as follows: VA, visual acuity; VF, visual field; NL, normal; CRHH, complete right homonymous hemianopia; CLHH, complete left homonymous hemianopia; IRHH, incomplete right homonymous hemianopia; ILHH, incomplete left homonymous hemianopia; PAP, papilledema; AVM, arteriovenous malformation; OTS, optic tract syndrome; APD, afferent pupillary defect; ellipses, no examination. defects and normal visual acuity. Con¬ versely, Frisen suggested that visual field defects due to optic tract lesions are usually complete. He attributed his findings to the small size of the tract. Five of our patients had com¬ plete homonymous hemianopias, two of which (cases 2 and 7) were surgical¬ ly induced. One additional patient (case 9) had a transiently complete hemianopia, and in another patient (case 1) the initially incomplete defect gradually completed. It seems clear that when visual field defects from optic tract lesions are incomplete, they tend to be incongru¬ ous. The value of incongruity in differ¬ entiating an optic tract lesion from a lesion of the lateral geniculate body or optic irradiation seems less clear. Savino et al3 suggested that "the pres¬ ence of gross incongruity is almost certainly a sign of optic tract involve¬ ment." Although our patients with incomplete homonymous field defects had obvious incongruity, the degree of incongruity present did not seem to be useful in distinguishing optic tract abnormalities from abnormalities of the lateral geniculate body or optic irradiation. Pupillary Abnormalities Pupillary defects associated with homonymous hemianopias have been recognized since 1883, when Wernicke8 summarized his own findings and those of earlier observers and sug- gested that stimulation of the nonseeing portion of the retina resulted in less reaction than that seen when the seeing portion was illuminated. This pupillary hemikinesia has always been extremely difficult to observe because of the tendency for light scat¬ ter, and many investigators have questioned its existence. In addition, Cibis et al9 used infrared pupillography and demonstrated hemihypokinesia in five patients with postgeniculate lesions, all of whom had normal visual acuity and ophthalmoscopic examination results. This finding would seem to greatly limit the diag¬ nostic usefulness of "Wernicke's pupil" in the diagnosis of pregeniculate lesions. A second pupillary sign associated with hemianopia was described by Behr,10 who noted that the pupil ipsi¬ lateral to the homonymous field defect tended to be slightly larger than that contralateral to the field defect. Although three of the patients in the series reported by Savino et al3 had slightly enlarged pupils on the side of the hemianopia, none of the patients reported by Bender and Bod¬ is-Wollner4 had such abnormalities, and we found no such abnormalities in patients. The most useful pupillary abnor¬ mality that is seen in patients with optic tract lesions seems to be a rela¬ tive afferent pupillary defect contraour lateral to the lesion. The presence of Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/07/2015 such a defect seems to relate directly to the degree of difference in the amount of visual field loss between the two eyes. Although approximately 65% of visual fibers cross in the optic chiasm of the cat, the percentage is substan¬ tially lower in primates. Ramon y Cajal" estimated that the ratio of crossing to noncrossing fibers was 2:1, but more recent studies suggest a ratio of 53:47.12 These findings corre¬ late well with observations of more receptor density on the nasal aspect of the retina than on the temporal aspect1314 and are in keeping with the larger size of the temporal field, which is 60% to 70% larger than the nasal field. This asymmetry led Bür¬ de15 to predict the occurrence of a relative afferent pupillary defect con¬ tralateral to an optic tract lesion. When Bell and Thompson7 reexamined their four patients with complete optic tract lesions and normal visual acuities, all four were found to have relative afferent defects. Previous series34 have found afferent pupillary defects in patients with ipsilaterally decreased visual acuity; however, as has already been noted, these patients undoubtedly had involvement of the ipsilateral optic nerve. It is the affer¬ ent pupillary defect that occurs in patients with complete or extensive homonymous hemianopia but without evidence of optic neuropathy that establishes the diagnosis of an optic tract syndrome without question. All of the patients in our study who had normal visual acuities and a com¬ plete homonymous hemianopia dem¬ onstrated a relative, contralateral afferent pupillary defect. Similarly, those patients with incongruous, incomplete field defects were all free of afferent defects except the patient with decreased acuity. The presence of a contralateral afferent pupillary defect in the setting of a complete homonymous hemianopia distin¬ guishes a tract lesion from involve¬ ment of the radiations. In addition, we have produced contralateral afferent pupillary defects in two monkeys in which the optic tract was sectioned without damage to the optic nerve. Similar studies have been reported by O'Connor et al.16 That the afferent pupillary defect seems to be depen¬ dent solely on the degree of visual field abnormality can be seen by the fact that an afferent pupillary defect developed in patient 1 in our series only after an incomplete homonymous hemianopia progressed to become complete, and patient 9 showed disap¬ pearance of an afferent pupillary defect as a complete homonymous hemianopia resolved into an incom¬ plete defect. In both patients, visual acuity and color vision remained nor¬ mal in both eyes, despite the changes in pupillary reactivity. These findings are also in keeping with recent studies by Thompson et al,17 suggesting that afferent pupillary defects correlate more closely with visual field defects than with visual acuity loss. Ophthalmoscopic Appearance The earliest recognition of retro¬ grade degeneration and resultant hemianopic nerve fiber layer and optic atrophy has been attributed by Hoyt and Kommerell18 to Lauber.19 The period necessary for retrograde degeneration following a pregenicu- late lesion is about six weeks. When such hemianopic changes are present, they signify a pregeniculate lesion or one that developed early in infancy. There is good evidence that transsynaptic degeneration does not occur in adults.20 Conclusions Our series reemphasizes the ten¬ dency for optic tract syndromes to occur in man. The study suggests that visual acuity is normal in such patients unless the optic nerves are also involved. Visual field defects are homonymous, often incomplete, and usually incongruous. When complete, they invariably are associated with an afferent pupillary defect contralater¬ al to the lesion. Hemianopic retinal and optic atrophy may occur six weeks following damage to the tract. References 1. Smith JL: Homonymous hemianopia: A review of 100 cases. Am J Ophthalmol 1962;54:616-622. 2. Trobe JD, Lorber ML, Schlezinger NS: Isolated homonymous hemianopia: A review of 104 cases. Arch Ophthalmol 1973;89:377-381. 3. Savino PJ, Paris M, Schatz NJ, et al: Optic tract syndrome: Review of 21 patients. Arch Ophthalmol 1978;96:656-663. 4. Bender MB, Bodis-Wollner I: Visual dys- function in optic tract lesions. Ann Neurol 1978;3:187-193. 5. Cogan DG: Neurology of the Visual System. Springfield, Ill, Charles C Thomas Publisher, 1967, p 250. 6. Frisen L: The neurology of visual acuity. Brain 1980;103:639-670. 7. Bell RA, Thompson HS: Relative afferent pupillary defect in optic tract hemianopias. Am J Ophthalmol 1978;85:538-540. 8. Wernicke C: Ueber hemiopische pupillen- reaction. Fortschr Med 1883;1:49-53. 9. Cibis GW, Campos EC, Aulhorn E: Pupillary hemiakinesia in suprageniculate lesions. Arch Ophthalmol 1975;93:1322-1327. 10. Behr C: Die Untersuchungsmethoden: II. Die Lehre von Pupillenbewegungen, in Graefe A, Saemische I (eds): Handbuch der gesamtem Augenheilkunde. Leipzig, East Germany, W Engelmann, 1924, vol 2, pp 115-117. 11. Ramon y Cajal S: Die Structur des Chiasma opticum, nebst einer allgemeinen Theorie der Kreuzung der Nervenbahnen. Leipzig, East Germany, Johann Ambrosius Barth, 1899. 12. Kupfer C, Chumbley L, Downer J: Quantitative histology of optic nerve, optic tract and lateral geniculate nucleus in man. J Anat 1967;101:393-401. 13. Osterberg G: Topography of the layer of rods and cones in the human retina. Acta Ophthalmol 1935;6(suppl):8. 14. Van Buren JM: The Retinal Ganglion Cell Layer. Springfield, Ill, Charles C Thomas Publisher, 1963, p 130. Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/07/2015 15. Burde RM: The pupil. Int Ophthalmol Clin 1967;7:849. 16. O'Connor PS, Kasdon D, Tredici TJ, et al: The Marcus Gunn pupil in experimental optic tract lesions. Ophthalmology 1982;89:160-164. 17. Thompson HS, Montague P, Cox TA, et al: The relationship between visual acuity, pupillary defect, and visual field defect. Am J Ophthalmol 1982;93:681-688. 18. Hoyt WF, Kommerell G: Der fundus oculi bei homonymer hemianopie. Klin Monatsbl Augenheilkd 1973;162:456-464. 19. Lauber H: Die ophthalmoskopische Differentraldiasnose der infra-und supranuclearen Hemianopsie, zugleich ein Beitrag zur Topographie des Faserverteilung in der Netzaut. Berud Versammml Deutsch Ophth Gesellsch 1927;46:89\x=req-\ 94. 20. Miller NR, Newman SA: Transsynaptic degeneration. Arch Ophthalmol 1981;99:1654.