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 Table of Contents  
ORIGINAL ARTICLE
Year : 2011  |  Volume : 1  |  Issue : 1  |  Page : 16-20

Optical coherence tomography (OCT) findings in patients with optic tract syndrome


1 Department of Ophthalmology, Kaohsiung Medical University, Kaohsiung, Taiwan
2 Department of Ophthalmology; Graduate Institute of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan
3 Department of Ophthalmology, Buddhist Tzu Chi General Hospital; Department of Ophthalmology and Visual Science, Tzu Chi University, Hualien, Taiwan
4 Department of Ophthalmology, Buddhist Tzu Chi General Hospital, Hualien, Taiwan

Date of Web Publication1-Dec-2011

Correspondence Address:
Rong Kung Tsai
Department of Ophthalmology, Buddhist Tzu Chi General Hospital, Tzu Chi University, 707, Section 3, Chung-Yung Road, Hualien 970
Taiwan
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Source of Support: None, Conflict of Interest: None


DOI: 10.1016/j.tjo.2011.08.003

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  Abstract 


Purpose: To analyze retinal nerve fiber layer (RNFL) thickness in eyes with optic tract syndrome (OTS) by using optical coherence tomography (OCT) and to evaluate the capability of OCT to detect the characteristic pattern of RNFL loss.
Methods: Eight patients (4 males and 4 females) with optic tract syndrome were enrolled in this retrospective collection of medical records. Characteristics including age, sex, etiology of optic tract lesion, visual acuity, visual field defect type were recorded. The diagnosis of optic tract syndrome were made by clinical history and typical optic disc findings, visual field defect and neuro-imaging findings including brain MRI and/or CT. The average of RNFL thickness of optic disc, four quadrants, specific four o’clock meridians and related parameters were analyzed and compared between both eyes.
Results: The nasal segment average of RNFL thickness was significantly lower in contralateral eyes than that of ipsilateral eyes (37.5 ± 6.7 μm and 67.9 ± 10.3 μm respectively; p < 0.001). The average RNFL thickness and mean thickness of other three quadrants were not significantly different between both eyes. The ratio of superior maximum to nasal segment (Smax/Navg), superior maximum to temporal segment (Smax/Tavg) and inferior maximum to temporal segment (Imax/Tavg) of were significantly different between both eyes (p < 0.001 in all comparisons). The RNFL thickness at nasal, temporal sectors of the contralateral and those at superior, inferior sectors of the ipsilateral eyes were significantly thinner than those of fellow eyes.
Conclusion: The RNFL thickness measured by OCT demonstrated a characteristic pattern of optic atrophies in OTS. The difference of nasal average, Smax/Navg, Smax/Tavg, Imax/Tavg values and specific radians between both eyes can provide useful information in the diagnosis of optic tract syndrome.

Keywords: nerve fiber layer thickness, optic tract syndrome, optic coherence tomography


How to cite this article:
Hsu CY, Lai YH, Hsu SY, Lin YC, Tsai RK. Optical coherence tomography (OCT) findings in patients with optic tract syndrome. Taiwan J Ophthalmol 2011;1:16-20

How to cite this URL:
Hsu CY, Lai YH, Hsu SY, Lin YC, Tsai RK. Optical coherence tomography (OCT) findings in patients with optic tract syndrome. Taiwan J Ophthalmol [serial online] 2011 [cited 2023 Mar 28];1:16-20. Available from: https://www.e-tjo.org/text.asp?2011/1/1/16/203092




  1. Introduction Top


Optic tract syndrome (OTS) is characterized by incongruous contralateral homonymous hemianopia, contralateral relative afferent pupillary defect (RAPD), and perpendicular pattern of optic atrophy in both eyes by a optic tract lesion.[1],[2] The diagnosis of OTS is made from clinical findings rather than radiological detection because the lesion is usually too small to be noted by neuro-imaging studies.

Optical coherence tomography (OCT) provides a reliable and reproducible retinal nerve fiber layer (RNFL) thickness measurements of the human eye and it has been used for estimation of reduction of RNFL thickness in glaucoma.[3],[4] OCT has been studied in several neuro-ophthalmic conditions, including anterior ischemic optic neuropathy, optic neuritis/multiple sclerosis, neu-romyelitis optica, migraine, pseudotumor cerebri, optic nerve head drusen, compressive optic neuropathy, Leber’s hereditary optic neuropathy and homonymous hemianopia.[5],[6] However, the reduction of the RNFL thickness in OTS has been seldom quantitatively assessed.[7],[8]

The purpose of this study was to demonstrate the unique pattern of RNFL thickness measured by OCT in patients with OTS. In addition, we will investigate the useful parameters of NFL thickness to contribute making a diagnosis of OTS.


  2. Material and methods Top


We retrospectively reviewed the medical records of patients with OTS diagnosed in the Department of Ophthalmology, Kaoh-siung Medical University Chung-Ho Memorial Hospital and the Department of Ophthalmology, Buddhist Tzu Chi Medical Center, between May 2006 and March 2010. This study has been approved by the Institutional Review Board (IRB) at Tzu Chi Medical Center. The duration between the ophthalmologic examinations (including OCT) and the time of optic tract injury longer than three months was inclusive to get stable data. The reason was based upon previous reports of OCT[9] and scanning laser polarimetry[10] findings in traumatic optic neuropathy that RNFL thickness decreased at 20 days after traumatic optic neuropathy and severe loss of RNFL was observed at day 90 and then ceased. Subject had a medical history of retinal disease or glaucoma was excluded. A total of 11 patients (6 males and 5 females) were enrolled. Among the 11 patients, one had a left optic tract syndrome concomitant with a left traumatic optic neuropathy and two others with OTS without OCT study were excluded. Therefore, OCT results from eight patients with pure optic tract lesion were analyzed. All patients had ophthalmologic examinations including the best corrected visual acuity (BCVA), pupil light reflex, funduscopy, disc photographs, Humphrey automated perimetry (central-30II program; Carl Zeiss Meditec, Inc., Dublin, CA), and neuro-imaging studies of MR imaging and/or computed tomography (CT) of brain. The peri-papillary RNFL thickness was evaluated by OCT (Carl Zeiss Meditec, Inc.) without pupil dilatation. The normal database was obtained from our previous study.[11]

The RNFL thickness was defined as the number of pixels between the anterior and posterior edges of the RNFL measured by means of OCT. Three circular scans, each 3.4 mm in diameter, centered on the optic disc were obtained, which were averaged by the average program inherent to the OCT software. Each OCT scan starts from the 9-o’clock position, which was reset as 0 degrees and succeeding scans were performed clockwise. In addition to average RNFL thickness of the entire circumference of the optic disc, 4 quadrants thickness including of superior (46 ~ 135 degrees), nasal (136 ~ 225 degrees for the right eye and 316 ~ 45 degrees for the left eye), inferior (226 ~ 315 degrees), temporal (316 ~ 45 degrees for the right eye and 136~225 degrees for the left eye) and ratio of superior to nasal, superior to temporal quadrant RNFL thickness were also recorded, which was the first parameter.[4],[11] The second parameter was specific thickness per 30 degree radian (superior sector: 75~105 degrees, nasal sector: 165~195 degrees for the right eye and 245 ~15 degrees for the left eye, inferior sector: 255 ~ 285 degrees, temporal sector: 245 ~ 15 degrees for the right eye and 165~195 degrees for the left eye). All parameters of RNFL thickness measurements taken from contralateral eyes were compared with the fellow eyes with paired t test. And the RNFL thickness in contralateral eyes was compared with those of normal Taiwanese database with unpaired t test. A P value less than 0.05 was accepted as statistically significant in all analyses.


  3. Results Top


A total of 8 patients (4 males and 4 females) with OTS were studied. The mean age at the time of OCT test was 38.1 ± 13.7 y/o ranging from 18.2 to 58 years. Descriptive data of these patients are summarized in [Table 1]. Etiology of OTS was trauma in 7 patients and periventricular leukomalacia in one patient. The mean peri-papillary RNFL thickness of the contralateral eyes was 91.4 ± 17.5 μm, 37.5 ± 6.7 μm, 101.5 ± 13.7 μm, and 45.0 ± 9.3 μmat the superior, nasal, inferior, and temporal quadrants, respectively. The total average thickness was 68.9 ± 9.5 μm. In the ipsilateral eye group, the mean RNFL thickness measured 80.5 ± 26.8 μm, 67.9 ± 10.3 μm, 93.3 ± 18.5 μm, and 50.5 ± 14.9 μm at the superior, nasal, inferior, and temporal quadrants, respectively. The total average measured 73.1 ± 15.1 μm [Table 2]. The nasal average of RNFL thickness was found to be significantly thinner in contralateral eyes than that of ipsilateral eyes (p < 0.001, [Table 2] and [Figure 1]. Actually, the RNFL thickness in total average and in 4 quadrants was all decreased in patients with OTS in both eyes as compared with that of normal Taiwanese people [Table 2]. The total average, as well as in other three quadrants, of RNFL thickness was not significantly different between both eyes. In 30 degree measurements, the mean RNFL thickness in contralateral eyes was 104.6 ± 27.4 μm, 34.3 ± 8.3 μm, 120.0 ± 17.2 μm, 29.8 ± 7.3 μmat the superior, nasal, inferior, and temporal sectors, respectively; and the mean RNFL thickness in the ipsilateral eyes measured 82.8 ± 31.1 μm, 63.0 ± 13.0 μm, 99.4 ± 22.3 μm, 49.6 ± 10.8 μmat the superior, nasal, inferior, and temporal sectors, respectively [Table 3]. The RNFL thickness at nasal, and temporal sectors in contralateral eyes was significantly thinner than those in ipsilateral eyes (p < 0.001). Comparing with those of normal Taiwanese, the specific RNFL thickness of all 4 directions (superior, nasal, inferior, and temporal sectors) in contralateral eyes as well as the superior, inferior and temporal sectors in ipsilateral eyes was also significantly thinner (all p < 0.05, [Table 3]. The parameter of the ratio of superior maximum to nasal quadrant average (Smax/Navg) values in the contralateral eyes and ipsilateral eyes was 3.8 ± 0.6 and 1.5 ± 0.4 respectively, which had statistically significant difference (p < 0.001, [Table 4]. Also, the ratio of superior maximum to temporal quadrant average (Smax/Tavg) and inferior maximum to temporal quadrant (Imax/Tavg) was statistically different between contralateral and ipsilateral eyes (Smax/Tavg 3.2 ± 0.4 v.s. 2.1 ± 0.3, Imax/Tavg 3.4 ± 0.6 v.s. 2.4 ± 0.4, respectively; p < 0.001, [Table 4]. Other parameters such as Imax/Smax and Smax/Imax between both eyes were not significant difference [Table 4].
Table 1: Demography of patients with optic tract syndrome

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Table 2: Retinal nerve fiber layer thickness in each quadrant of patients with optic tract syndrome (N = 8)

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Table 3: Retinal nerve fiber layer thickness in definite sectors of patients with optic tract syndrome (N = 8)

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Table 4: Comparison of parameters in OCT between both eyes of patients with optic tract syndrome (N = 8)

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Figure 1: Box plot chart of RNFL thickness in average and four quadrants between both eyes. The nasal quadrant of RNFL thickness in contralateral eyes (shaded box) was significantly less than that of ipsilateral eyes (open box). *P < 0.05 (paired t test) (C: contralateral eyes; I: ipsilateral to the optic tract lesion side).

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  4. Case description (Case 1) Top


A 48-year-old woman complained of blurred vision in the right side after a traffic accident 4 months ago. The BCVA was 1.0 in right eye and 0.8 in left eye respectively. There was no apparent RAPD between both eyes. Fundoscopy demonstrated a temporal pale appearance of disc in right eye and a band atrophy of disc in left eye. The axis of cupping was different between both eyes. Humphrey automated perimetry revealed a left homonymous hemianopia. A diagnosis of right optic tract syndrome was made. Brain MR-imaging study showed no space occupying lesion in the area of right optic tract.OCT examinations disclosed the RNFL thickness at temporal and superior quadrant in right eye were thinner than that of left eye. The nasal quadrant of RNFL thickness was decreased in left eye, as expected in patients with right optic tract syndrome [Figure 2].
Figure 2: Representative of patients with optic tract syndrome. A 48-year-old woman was diagnosed as right optic tract syndrome caused by brain contusion in a motor vehicle crash. A. Optic disc findings showed pale appearance in the inferior to temporal disc in right eye and band atrophy appearance in left disc at 4 months after injury. The axis of cupping was different between both eyes. B. Simultaneous OCT analysis revealed a reduction of RNFL thickness at superior and inferior segment in right eye as well as a reduction of RNFL thickness at nasal and temporal segment in left eye. C. Humphrey automatic perimetry showed a left-sided incongruous homonymous hemianopia.

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  5. Discussion Top


OTS is diagnosed as contralateral incongruous homonymous hemianopia, contralateral RAPD, and a characteristic pattern of optic atrophy in each eye due to retrograde axonal degeneration. In the eye ipsilateral to the optic tract lesion, damage of the nerve fiber only involves the uncrossed, arcuate temporal bundles, which enter the disc at the superior and inferior poles. Subsequently, the ipsi-lateral optic disc shows a temporal pale appearance after an optic tract lesion. In contralateral eyes, the corresponding damage of crossed retinal fibers involves the papillomacular fibers and the nasal radiating fibers, which result in atrophy in the nasal and temporal horizontal portions of the disc, so-called the band or bow-tie atrophy.[2]

Indeed, our results clearly demonstrated that OCT can successfully quantitate the RNFL thickness reduction corresponding to the characteristic ophthalmoscopic findings of optic atrophy in OTS. This is the first case series report to demonstrate the RNFL thickness decrease by OCT in eyes with OTS by PubMed searching in the English literature. In contralateral eyes, the nasal quadrant average values of RNFL thickness were significantly thinner than that of ipsilateral eye. Consistent with previous case reports, the thinner RNFL in the nasal quadrant of contralateral eye is indicative of RNFL loss in nasal radiation and respects the visual field defect of temporal henianopia.[7],[8] The average of RNFL thickness in temporal quadrant was also thinner in contralateral eyes than in ipsilateral eyes but without statistically significant difference. With preserving the superior and inferior arcuate of nerve fiber in the contralateral eyes in OTS, the mean ratio of Smax/Navg, Smax/Tavg and Imax/Tavg is significantly higher in contralateral eyes than in ipsilateral eyes (p < 0.001). In the ipsilateral eyes, temporal pale of optic disc for uncrossed, arcuate temporal bundles damage is characteristic. The superior quadrant of RNFL thickness was thinner in the ipsilateral eyes than that of the contralateral eyes. Inferior average of RNFL thickness was also thinner than that in contralat-eral eyes. However, both of them were not statistically significant. Measuring the RNFL around the disc into 30 degrees’ radians, the RNFL thickness at nasal, temporal sectors of contralateral eyes and those at superior, inferior sectors of ipsilateral eyes were significantly thinner than those of corresponding areas of fellow eyes. This observation implies that measurement of RNFL thickness with 30 degrees’ radians has stronger correlations with visual field defect patterns than four-quadrant divisions in patients with OTS. Surprisingly, our results demonstrated that RNFL thickness in total average, in four separate quadrants, even at superior, nasal, inferior and temporal sectors in the contralateral eyes of patients with OTS were decreased as compared with those of normal Taiwanese database.[11] This finding is consistent with several reports in patients with OTS and in patients with bilateral band atrophy caused by chiasmal lesions.[7],[12],[13] It has been suggested that the loss of RNFL in contralateral eyes occurs predominantly in the nasal and temporal quadrants, the superior and inferior area of the disc also lost approximately about 50% of their fibers, as axons originating from the nasal retina also penetrate in the superior and inferior part of optic disc.[13] Further studies are required to dissect this general thinning of NRNFL thickness in contralateral eyes of patients with OTS. In the ipsilateral eyes, as expected, the RNFL thickness decreased at superior and inferior sectors but preserving nasal sector as compared to those of normal. At temporal sector in the ipsilateral eyes, the RNFL thickness is still significant thinner than that of normal. This observation is explained that papillomacular bundle fibers entering optic disc at temporal sector contains both fibers originating from nasal retinas and temporal retinas.

Limitations of our study are small case number and retrospective observation. The severity of visual field defects and variable durations after injury among individuals with OTS will affect the value of RNFL thickness measurement. However, OCT is a promising instrument for the evaluation of the RNFL in patients with OTS. Using 30 degrees division around the disc, the RNFL thickness loss pattern respects the specific type of visual field defect in each eye. In conclusion, our results demonstrated that OCT can detect RNFL reduction with site-dependent optic nerve degeneration in patients with OTS. The useful information is helpful in diagnosing and management of optic tract syndrome.

 
  References Top

1.
Miller NR, Newman NJ. Chapter 8. Topical diagnosis of lesions in the visual sensory pathway. In: Miller NR, Newman NJ, editors. Clinical neuro-ophthalmology. 5th ed. Baltimore: William & Wilkins; 1998. p. 237-386.  Back to cited text no. 1
    
2.
Savino PJ, Norman J, Schatz NJ, Orr LS, Corbett JJ. Optic tract syndrome. Arch Ophthalmol 1978;96:656-63.  Back to cited text no. 2
    
3.
Guedes V, Schuman JS, Hertzmark E, Wollstein G, Correnti A, Mancini R, et al. Optical coherence tomography measurement of macular and nerve fiber layer thickness in normal and glaucomatous human eyes. Ophthalmol 2003;110:177-89.  Back to cited text no. 3
    
4.
Kanamori A, Nakamura M, Escano MF, Seya R, Maeda H, Negi A. Evaluation of the glaucomatous damage on retinal nerve fiber layer thickness measured by optical coherence tomography. Am J Ophthalmol 2003;135:513-20.  Back to cited text no. 4
    
5.
Subei AM, Eggenberger ER. Optical coherence tomography: another useful tool in a neuro-ophthalmologist’s armamentarium. Curr Opin Ophthalmol 2009;20:462-6.  Back to cited text no. 5
    
6.
Mehta JS, Plant GT. Optical coherence tomography (OCT) findings in congenital/ long-standing homonymous hemianopia. Am J Ophthalmol 2005;140:727-9.  Back to cited text no. 6
    
7.
Tatsumi Y, Kanamori A, Kusuhara A, Nakanishi Y, Kusuhara S, Nakamura M. Retinal nerve fiber layer thickness in optic tract syndrome. Jpn J Ophthalmol 2005;49:294-6.  Back to cited text no. 7
    
8.
Monteiro MLR, Hokazone K. Retinal nerve fiber layer loss documented by optical coherence tomography in patients with optic tract lesions. Rev Bras Oftalmol 2008;68:48-52.  Back to cited text no. 8
    
9.
Medeiros FA, Moura FC, Vessani RM, Susanna Jr R. Axonal loss after traumatic optic neuropathy documented by optical coherence tomography. Am J Oph-thalmol 2003;135:406-8.  Back to cited text no. 9
    
10.
Miyahara T, Kurimoto Y, Kurokawa T, Kuroda T, Yoshimura N. Alterations in retinal nerve fiber layer thickness following indirect traumatic optic neuropathy detected by nerve fiber analyzer, GDx-N. Am J Ophthalmol 2003;136:361 -4.  Back to cited text no. 10
    
11.
Hsu SY, Tsai RK. Analysis of retinal nerve fiber layer and macular thickness measurements in healthy Taiwanese individuals using optical coherence tomography (Stratus OCT). J Glaucoma 2008;17:30-5.  Back to cited text no. 11
    
12.
Kanamori A, Nakamura M, Matsui N, Nagai A, Nakanishi Y, Kusuhara S. Optical coherence tomography detects characteristic retinal nerve fiber layer thickness corresponding to band atrophy of the optic discs. Ophthalmol 2004;111:2278-83.  Back to cited text no. 12
    
13.
Monteiro ML, Leal BC, Rosa AA, Bronstein MD. Optical coherence tomography analysis of axonal loss in band atrophy of the optic nerve. Br J Ophthalmol 2004;88:896-9.  Back to cited text no. 13
    


    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]


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