General characteristics are summarized in for the seven male and six female subjects. Ten of them met clinical criteria for CFEOM3 and were TUBB3-mutation positive, whereas subjects 11 and 12 did not have CFEOM3 but were TUBB3-mutation positive, and subject 13 did not have CFEOM3 and was TUBB3-mutation negative. Subject 13 was included as an immediate family member of affected, mutation-positive subjects, to provide insight into the effects of family genetic background. The mean age of subjects with the CFEOM3 phenotype was 45 ± 6 years (mean ± SEM, range, 17–74), whereas clinically unaffected subjects had an average age of 18 ± 3.2 years (range 14 – 24). Although not tested formally, the subjects had generally normal intellectual function, although several reported having had developmental delay as children.
Characteristics of Subjects in Pedigrees with CFEOM3
Comparisons are provided here with previously published rectus EOM data from 21 normal volunteers, 10 men and 11 women, who underwent MRI with the current technique with an 8-cm quasicoronal FOV.24
Six normal volunteers underwent MRI of the CNs in the skull base. Ten control subjects who contributed rectus and superior oblique (SO) EOM data had an average age of 20 ± 1 years (mean ± SEM; range, 14–28). An additional 13 control subjects of average age 23 ± 1 years (range, 14–33) underwent higher resolution MRI of the optic nerves (ONs) in quasicoronal planes with a 6-cm FOV, and 10 subjects underwent MRI of the IO muscles in the quasisagittal planes. All control subjects had normal ocular and lid motility and visual acuity in each eye correctable to 0 logarithm of the minimum angle resolvable in arcmin (logMAR, 20/20), or better.
Clinical Findings in CFEOM3
Overall, subjects with CFEOM3 had slightly subnormal visual acuities. The mean corrected visual acuity of the subjects exhibiting the CFEOM3 phenotype was 0.29 ± 0.08 averaged over the two eyes (). The mean corrected visual acuity of the two eyes of the three clinically unaffected subjects was normal at −0.03 ± 0.02 logMAR.
All subjects exhibiting the CFEOM3 phenotype had symmetrical pupils ranging in diameter from 5 to 8 mm and normal pupillary reactions, without afferent pupillary defect or light-near dissociation. The ophthalmoscopic appearance of the ON head was normal in all subjects with CFEOM3 except for subject 3, who had unilateral, and subject 4, who had bilateral ON hypoplasia. Unaffected, mutation-negative subject 13 had unilateral ON hypoplasia.
Subjects with CFEOM3 had unilateral or mild bilateral blepharoptosis. Four had unilateral blepharoptosis, and six had bilateral blepharoptosis. Seven subjects who exhibited the CFEOM3 phenotype had undergone one to two surgeries each for blepharoptosis.
All subjects who exhibited the CFEOM3 phenotype had undergone 1 to 15 strabismus surgeries. Even after strabismus surgeries, all subjects exhibiting the CFEOM3 phenotype had limited supraduction and were exotropic in some gaze positions. Although subjects 1, 4, 5, 7, 8, 9, and 10 had normal vertical binocular alignment, subjects 2, 3, and 6 had hypotropia due to asymmetric limitation of supraduction. Affected subjects 4, 5, 7, 9, and 10 exhibited abduction of one eye in deorsumversion (binocular downward gaze), and subjects 1 to 3 exhibited increased exotropia in deorsumversion, constituting a λ- or A-pattern incomitance. Bell's phenomenon was absent in all orbits of affected subjects, with the exception of subject 5, who exhibited normal Bell's phenomenon in her externally unaffected right eye.
Because of the heterogeneity of the CFEOM3 phenotype within pedigrees, informative features are described for each affected subject.
Ocular Motility in Subjects Manifesting the CFEOM3 Phenotype
D417N Amino Acid Substitution.
Subject 1 from pedigree D was a 26-year-old woman who harbored the D417N TUBB3 amino acid substitution and had CFEOM3 and a progressive sensorimotor axonal neuropathy that is common to this and several other specific TUBB3
She had undergone surgery for left-side blepharoptosis at 8 months of age and strabismus surgeries of the left eye at 9 and 11 years. Left eye supraduction and adduction were markedly limited, right eye adduction was mildly limited, and the both eyes abducted markedly during deorsumversion (binocular downward gaze, ). Levator function was decreased to 4 mm on the left and was normal at 16 mm on the right.
Figure 1. Subject 1 with the CFEOM3 phenotype, exhibiting left-side blepharoptosis, limited supraduction and adduction, and λ-pattern exotropia. Ductions were are normal for the right eye. The eyelids were manually elevated for photography in deorsumversion. (more ...)
Subject 2, also from pedigree D, was a 57-year-old woman and the mother of patient 1. She also harbored the D417N amino acid substitution and had both CFEOM3 and later-onset upper and lower extremity weakness and sensory loss. She was born with exotropia, limited supraduction, and blepharoptosis greater on the right side than on the left. She underwent multiple eyelid and numerous strabismus surgeries in childhood and bilateral frontalis suspension surgery for eyelid elevation at 27 years of age. The left but not right eye exhibited high myopia and astigmatism, but vision in both eyes was correctable with spectacles to 0.1 logMAR. There was fine, horizontal, spontaneous nystagmus in central gaze and convergence nystagmus in levoversion. Neither eye supraducted above horizontal midposition. The left eye adducted markedly in attempted supraversion and abducted markedly in attempted deorsumversion. Levator function was absent on the right and mildly subnormal at 10 mm on the left.
Subject 12 from pedigree D was the 24-year-old son of subject 2 and was clinically unaffected, despite harboring the D417N amino acid substitution. Visual acuity in each eye was normal after correction of low myopia. Lid position and ocular motility were normal as was stereopsis when tested by the Titmus method at 40 arcsec. The ONs also appeared normal. The subject had no symptoms of peripheral neuropathy.
R262C Amino Acid Substitution.
Subject 3 from pedigree AT was a 17-year-old boy who harbored the R262C substitution and had a mild intellectual deficit. He had A-pattern horizontal strabismus manifested by esotropia in supraversion and exotropia in infraversion (). In his right eye, he had blepharoptosis with limited adduction, supraduction, and infraduction. Lid position and ductions of the left eye were normal. The right ON was clinically hypoplastic, exhibiting the double-ring sign of a bare scleral annulus encircling an attenuated central ON head.
Figure 2. Subject 3 with the CFEOM3 phenotype limited to the right eye, which exhibited blepharoptosis and limitation of supraduction, infraduction, and adduction. The subject had A-pattern strabismus, with esotropia in supraversion, and exotropia in infraversion. (more ...)
Subject 4, also from AT and harboring the R262C substitution, was a 32-year-old man with bilateral congenital blepharoptosis, absence of vertical versions, exotropia, bilaterally limited adduction, and conjugate horizontal nystagmus. Although both ONs were ophthalmoscopically hypoplastic, visual acuity was 0.8 logMAR in the right eye and was essentially normal at 0.05 logMAR in the left eye. The right eye abducted in deorsumversion, whereas the left eye abducted poorly under all conditions.
Subject 5, also from AT and harboring R262C, was a 39-year-old woman who had congenital left blepharoptosis and limitation of abduction, supraduction, and infraduction, with aberrant abduction during both infraversion and attempted lid closure during examination to evaluate Bell's phenomenon. Right eye motility was normal, and she was exotropic in central gaze (). Visual acuity was 0.4 logMAR in the affected left eye.
Figure 3. Subject 5 from pedigree AT with the CFEOM3 phenotype exhibiting left-side congenital blepharoptosis and limitation of abduction, supraduction, and infraduction, with synkinetic abduction in both infraversion and lid closure. Right eye motility was normal. (more ...)
Subject 11 from pedigree AT was a 14-year-old boy who harbored the R262C mutation and was clinically unaffected. Visual acuity in each eye was normal after correction of low myopia. Lid position and ocular motility were normal, but stereopsis determined by the Titmus method was slightly subnormal at 80 arcsec. The ONs appeared normal.
Subject 13 from pedigree AT was a 15-year-old boy who was mutation negative and clinically unaffected. Visual acuity in each eye was at least 0.0 logMAR after correction of low myopia. Lid position and ocular motility were normal, as well as stereopsis by the Titmus method at 40 arcsec. The left ON exhibited a double-ring sign suggestive of mild ON hypoplasia.
Subject 6 was a 48-year-old woman from pedigree BT, who harbored R262C (). She had right blepharoptosis that had not been treated surgically. Although both eyes had limited supraduction, the limitation was greater in the right eye, creating right hypotropia. The left eye abducted and, paradoxically, supraducted on attempted deorsumversion, whereas the left eye adducted in attempted supraduction.
Figure 4. Subject 6 from pedigree BT with the CFEOM3 phenotype who had right blepharoptosis and right hypotropia, A-pattern strabismus, and paradoxical supraduction and abduction of the left eye on attempted deorsumversion. Both eyes had limited supraduction. Unable, (more ...)
Subject 7, also from pedigree BT and R262C positive, was a 67-year-old woman who had bilateral blepharoptosis and complete ophthalmoplegia except for adduction of the left eye and abduction of the right eye on attempted infraduction. Convergence was absent. Visual acuity was 0.25 and 0.40 logMAR in the right and left eyes, respectively. The subject had undergone bilateral surgery for blepharoptosis and exotropia and bilateral IR tenotomy, to mitigate severe bilateral limitation of vertical gaze to deorsumversion only.
Subject 8 from pedigree QX harbors the 262C substitution and was a 33-year-old man with bilateral congenital blepharoptosis, large angle exotropia, and bilaterally fixed deorsumversion. He had nearly complete ophthalmoplegia, except for abduction of both eyes and for the transient ability to align the eyes during proximal convergence. Visual acuity was 0.2 and 0.1 logMAR for the right and left eyes, respectively. He exhibited disconjugate, jerky horizontal nystagmus. Both IR muscles had been surgically transected before examination.
Subject 9 from pedigree QX harbored the R262C substitution and was a 74-year-old woman with bilateral congenital blepharoptosis, large angle exotropia, and bilaterally fixed deorsumversion. She had undergone surgeries for blepharoptosis and strabismus. Visual acuity was counting fingers in the right eye and 0.2 logMAR in the left eye. She had nearly complete ophthalmoplegia, except for abduction of the right eye in attempted infraduction. Both eyes incycloducted in attempted infraduction, suggesting bilateral SO function. Both IR muscles had been surgically transected before her examination.
Subject 10 from pedigree QX harbored the R262C substitution and was a 53-year-old man with bilateral congenital blepharoptosis, large angle exotropia, and bilaterally fixed deorsumversion. He had undergone surgeries for blepharoptosis and strabismus. Visual acuity was 0.2 in the right eye and 0.4 logMAR in the left eye. He had nearly complete ophthalmoplegia, except for abduction of the left eye in attempted infraduction, and limited adduction with slow adducting saccades bilaterally. Both eyes incycloducted in attempted infraduction, suggesting bilateral SO function. Claustrophobia precluded MRI in this subject.
MRI Findings in CFEOM3
All except subject 10 underwent MRI. The three affected subjects (8, 9, and 10) in pedigree QX harbored the R262C substitution and exhibited the most severe ocular findings, with exotropia and infraduction and almost total external ophthalmoplegia, except for residual abduction and limited incycloduction on attempted infraduction. Subject 8 could intermittently achieve binocular alignment by proximal convergence. MRI findings in severely affected subjects 8 and 9 revealed profound bilateral hypoplasia of the SR, LPS, and MR muscles ( and ). Both subjects also exhibited highly aspheric globes (), a feature that had been observed in members of a large CFEOM3 pedigree25
now known to harbor the R262C substitution.16
Figure 5. Quasicoronal T2 FSE MRI in subject 9 with a severe CFEOM3 phenotype. Image planes are 2 mm thick with a 4-mm gap between them, arranged from posterior at top to anterior at bottom. There was marked bilateral hypoplasia of the LPS, SR, and MR. The IR was (more ...)
Figure 6. Quasi-sagittal T2 FSE MRI in subject 9 with a severe CFEOM3 phenotype, exhibiting severe bilateral hypoplasia of the LPS and SR muscles, as well as bilateral absence of the IO muscle. An epithelial inclusion cyst and artificial IOL were present in the (more ...)
Other subjects exhibited a less severe, asymmetrical phenotype. For example, EOMs in the right orbit of subject 1 from pedigree D appeared normal on quasicoronal () and quasisagittal () MRIs, yet in the left obit, there was marked hypoplasia of the LPS and the deep portions of the SR, MR, and IO muscles. Thus, MRI findings in the left but not right orbit of subject 1 were compatible with the CFEOM1 phenotype.
Figure 7. Quasicoronal T1 MRI in phenotypically less affected subject 1, with asymmetric hypoplasia of the left LPS and milder hypoplasia of the deep portion of the left MR and SR muscles. The inferior division of the left oculomotor nerve (CN3) was in contact (more ...)
Figure 8. Quasisagittal T1 MRI in less affected subject 1, in whom only the left eye was phenotypically involved. The subject exhibited hypoplasia of the involved left LPS and SR muscles, as well as severe hypoplasia of the left IO muscle in this image plane. The (more ...)
Quantitative Features of EOMs
EOM volumes in affected subjects with CFEOM3 were subnormal for the SR, MR, and IR (). This effect was significant at the 0.0002 level for the SR and at the 0.02 level for the MR and IR. IO volume was slightly but not significantly subnormal, and LR volume was slightly but not significantly greater than normal. Subjects with CFEOM3 who had evidence of surgical IR disinsertion had displacement of the IO belly without significant change in IO volume. Such an IO path change would not have been expected to change apparent IO volume. On average, externally unaffected members of families with CFEOM3 had normal EOM volumes. However, the total number of unaffected family members who were studied was small, and externally unaffected subject 12, who carried the D417N substitution, exhibited in his left orbit volume reductions of the SR (220 mm3), MR (278 mm3), and IR (246 mm3) that were below the 2.5 percentile for normal EOM volumes. Subject 12 had no other subnormal EOM volumes, and subjects 11 and 13 did not have any subnormal EOM volumes. Subject 12 was thus regarded as carrying the endophenotype of CFEOM3.
Muscle Volumes in Control Subjects and Subjects with the CFEOM3 Phenotype
Extraocular Muscle Dysplasia
In externally affected subjects 4, 5, 7, 8, and 9, the LR exhibited a longitudinal fissure separating it into distinct superior and inferior zones. Such fissuring was also evident in externally unaffected subjects 11 and 12, who carried the R262C and D417N substitutions, respectively. In addition, in the left orbit of subject 12, CN3 was in continuity with the inferior zone of the LR, whereas CN6 entered the superior zone. All other EOMs were free of dysplasia in the remaining subjects with CFEOM3 who underwent MRI.
Globe Position and EOM Paths
Coordinates of the LR, MR, and SR pulleys in subjects exhibiting the CFEOM3 phenotype were not significantly different from normal (P > 0.05), and the lateral coordinate of the IR pulley was minimally abnormal, as a likely result of IR disinsertion surgeries that had been performed in nearly all affected orbits.
Imaging of Intraorbital Motor Nerves
Orbits affected by CFEOM3 exhibited abnormal motor innervation, in approximate proportion to the degree of clinical motility restrictions. It was possible to visualize the inferior but not the superior division of CN3 in the subjects with CFEOM3 who were imaged. The superior division was seen, however, only in a subset of normal subjects. In some subjects with CFEOM3, the inferior division of CN3 was too small to trace its branches.
Image resolution was insufficient for quantitative analysis of intraorbital motor nerve size.24
When the nerve was of sufficient size to trace, however, MRI demonstrated misinnervation of EOMs in some subjects with CFEOM3. The inferior division of CN3 failed to innervate the MR in subjects 2, 3, 6, and 7 and was in intimate continuity with the inferior zone of the LR as well its normal target EOMs in subjects 2, 6, 7, and 9 (). In subjects 1, 2, 4, 8, 9, and 10, CN6 entered the superior zone of the LR, whereas a branch of CN3 was in continuity with the inferior zone (). Contraction of the LR in infraduction would explain exotropia in that gaze position, with relaxation in supraduction accounting for the associated esotropia in that gaze position.
Functional imaging in subject 1 was also consistent with LR misinnervation. In subjects 1 and 2 from pedigree D, one LR exhibited contractile thickening in attempted infraduction (). Although subjects 4, 5, 7, 9, and 10 also exhibited abduction on attempted infraduction, MRI could not be performed in this situation because infraduction to a target could not be maintained in the scanner. Misinnervation of the LR by a CN3 branch normally destined for the IR appears to account for the A- and λ-pattern strabismus in pedigrees D and AT and for the anomalous abduction in attempted infraduction in pedigrees BT and QX.
Figure 9. Coronal MRI of left orbit of subject 2 with CFEOM3, illustrating anomalous contractile thickening of LR with the fellow right eye fixating in infraduction. The subject had hypoplasia of the MR and superior rectus/levator (SR/LPS) muscles. SOV, superior (more ...)
Imaging of Intracranial Motor Nerves
-weighted imaging of the skull base region has sufficient resolution to demonstrate easily and consistently the course of CN3 of normal subjects.26
CN3s were strikingly hypoplastic ipsilateral to all affected orbits, except for the nearly normal left CN3 of subject 5. CN3 was of normal size in subject 1's unaffected right orbit and was of normal size bilaterally in the clinically unaffected family members, regardless of mutation status (). No orbit was affected by the clinical CFEOM3 phenotype when the subarachnoid oculomotor nerve ipsilateral to that orbit had a width of at least 1.9 mm. For comparison, normal CN3 width measured using this technique is 2.01 ± 0.36 mm.26
Asymmetry of subarachnoid CN3 size is illustrated in for subject 1. The left CN3 was affected with a width of 1.05 mm, whereas on the right side, CN3 was normal, with a width of 2.01 mm.
Duction Abnormalities and Oculomotor Nerve Width in Members of Families Affected by CFEOM3
Heavily T2-weighted MRI of the subarachnoid oculomotor nerve (CN3) in subject 1 with a unilateral left CFEOM3 phenotype. The right CN3 was normal at 2.0 mm wide, whereas the left CN3 was subnormal at 1.0 mm wide.
In normal subjects, the heavily T2
-weighted imaging technique also demonstrates the course of CN6 after it exits the pons.27,28
The CN6 was unilaterally or bilaterally hypoplastic in subjects 7, 8, and 9 with the CFEOM3 phenotype; abnormalities of CN6 were not evident in the remaining subjects.
ON cross sections normally decrease anteriorly to posteriorly, because of the reduction of connective tissues surrounding axon bundles.29
Thus, ON cross section was analyzed as closely as possible posterior to the globe-ON junction. Subjects with the CFEOM3 phenotype exhibited mean ON cross sections of 9.19 ± 0.60 mm2
, which was a 35% reduction and significantly smaller than the mean of 14.1 ± 0.77 mm2
for 17 control ONs (P
< 0.00005). All ophthalmoscopically hypoplastic ONs exhibited reduced MRI cross sections, yet not all ONs with reduced MRI cross sections were ophthalmoscopically hypoplastic. The ophthalmoscopic finding of ON hypoplasia was concordant with MRI in subject 4, whose right ON had a cross section of 4.3 and left ON had cross section of 4.8 mm2
. The unilateral ophthalmoscopic finding of the double-ring sign indicative of right ON hypoplasia in subject 3 also correlated with reduction in MRI cross section to 7.5 mm2
, compared with 13.1 mm2
on the ophthalmoscopically left side. Subject 3 also had a dysplastic corpus callosum on sagittal MRI. The ophthalmoscopically hypoplastic left ON of CFEOM3-unaffected, mutation-negative subject 13 had a subnormal cross section of 8.0 mm2
, compared with 10.0 for his ophthalmoscopically normal right ON. However, ONs were ophthalmoscopically normal in on the right-affected subject 8, whose right ON cross section was 7.0 mm2
, and on the left in affected subject 1, whose left ON cross section was 6.7 mm2
The facial nerve was bilaterally normal in all subjects imaged. Consistent with this, no subject exhibited clinical signs of facial weakness, and we have not found facial weakness to cosegregate with either the R262C or D417N substitutions.16