Sagging eye syndrome (SES) is an acquired strabismus caused by age-related degeneration of the connective tissue (especially the LR-SR band) between the extraocular muscle pulleys, leading to inferior displacement (sagging) of the lateral rectus (LR) pulley. It was first reported by Rutar and Demer in 2009.
It is characterized by a combination of horizontal strabismus (esotropia) and vertical strabismus, along with bilateral aponeurotic blepharoptosis and deepening of the upper eyelid sulcus. It is distinct from heavy eye syndrome (HES), which presents with esotropia and hypotropia associated with axial high myopia, and the two conditions are clearly differentiated.
It is a common cause of acquired diplopia. In a study by Goseki et al., approximately 31% of 945 patients (mostly aged 60–80 years) with diplopia had sagging eye syndrome, and about 60% were female. The prevalence was only 4.7% in those under 50 years but reached 60.9% in those over 90 years. Onset is most common between ages 60 and 80, with a higher prevalence in women (54%) and in myopic eyes 1). Many cases previously attributed to unexplained trochlear nerve palsy or divergence palsy are now thought to fall under this disease concept.
Sagging eye syndrome is caused by age-related degeneration of the pulley connective tissue, presenting with small-angle esotropia or vertical strabismus. In contrast, heavy eye syndrome is associated with axial high myopia (usually -8D or more, axial length 27 mm or more), causing large-angle esotropia and hypotropia, with marked restriction of eye movement.
Typical presentation is slow or subacute onset of diplopia in elderly patients1).
Neurological examination is normal, and no cranial nerve palsy is observed. There may be a history of eyelid surgery, facelift, or cataract surgery.
The following age-related changes in the ocular adnexa are observed: note the sunken upper eyelid and bulging lower eyelid.
Sagging eye syndrome is classified into two types: age-related distance esotropia (ARDE) and cyclovertical strabismus (CVS), each with distinct clinical features.
Age-related distance esotropia
Incomitant esotropia: worsens at distance and on lateral gaze, with orthophoria or only a small phoria at near.
No vertical deviation: only horizontal deviation without a vertical component.
Normal horizontal eye movements: horizontal range of motion and saccadic velocity are normal.
Cycloverical strabismus
Hypotropia + excyclotorsion: hypotropia and excyclotorsion of the lower eye.
Incomitant vertical strabismus: Horizontal deviation may not be present.
Elevation deficit: Upward eye movement may be limited.
Age-related distance esotropia with cycloverical strabismus
Combined type: Incomitant esotropia with a small unilateral hypotropia.
Cyclotorsion: Present in 65% of patients with sagging eye syndrome.
The deviation in sagging eye syndrome is usually small, at 10 prism diopters (PD) or less. During near vision, fusional ability (the ability to integrate images from both eyes into one) is sufficiently maintained, allowing compensation for small-angle deviations, and patients do not experience diplopia.
The underlying cause of sagging eye syndrome is degeneration of the connective tissue connecting the extraocular muscle pulleys (especially the LR-SR band) associated with aging. The detailed pathogenesis is described in the section “Pathophysiology and Detailed Mechanism”.
The main risk factors are as follows:
Diagnosis is primarily based on clinical findings. The combination of a deviation pattern (large esotropia at distance and small at near) on sensorimotor examination and age-related changes of the ocular adnexa (ptosis, deepening of the superior sulcus) provides diagnostic clues. The deviation pattern in sagging eye syndrome does not match that of cranial nerve palsy or alternating hypertropia. Normal horizontal saccades and horizontal eye movement range are also important differentiating points.
MRI is useful for confirming the diagnosis but is not mandatory. Head MRI shows inferior displacement and lateral tilt of the lateral rectus muscle, and disruption or stretching/thinning of the LR-SR band.
Patel et al. conducted an imaging study of 100 subjects without strabismus and showed that the LR-SR band was visible in 95% of eyes on non-fat-suppressed coronal T1-weighted images and 68% on coronal STIR images. Discontinuous bands were found in 5% and superolateral bowing in 24%, considered evidence of connective tissue degeneration with normal aging.
Because patients with ptosis syndrome are in an age group with risk factors for stroke or tumor, careful differential diagnosis is required1).
| Differential diagnosis | Main differences from ptosis syndrome |
|---|---|
| Abducens nerve (CN VI) palsy | Limited abduction, nystagmus on abduction |
| Trochlear nerve (CN IV) palsy | Superior oblique muscle weakness, positive Bielschowsky test |
| Thyroid eye disease | Positive forced duction test, extraocular muscle hypertrophy |
| Myasthenia gravis | Diurnal variation of symptoms, positive fatigue test |
| Decompensated heterophoria | History of strabismus since childhood |
| Heavy eye syndrome | High myopia (≥ -8D), large angle deviation |
Most patients with heavy eye syndrome have good fusion ability and do not experience diplopia at near. If the deviation is small and does not interfere with daily life, observation without intervention is possible.
Since the deviation in sagging eye syndrome is usually 10 PD or less, prism correction is effective. It is well managed with prisms or strabismus surgery 1).
Because near fusion ability is strong, an advantage is that improving distance diplopia does not induce near diplopia. Surgery is offered to patients who do not use glasses and do not wish to use them in the future.
Patients who do not respond to prisms or do not desire prisms are candidates.
In a 2020 review, strabismus surgery was performed in 50% of all cases of sagging eye syndrome. The mean preoperative distance esotropia was 6.9 ± 0.7Δ, which improved to 0.3 ± 0.3Δ postoperatively, and the mean vertical deviation decreased from 3.0 ± 0.3Δ to 0.7 ± 0.2Δ.
Because sagging eye syndrome is a degenerative disease, connective tissue degeneration may further progress after surgery, and strabismus may recur (in up to 20% of patients). It is important to receive an explanation of this possibility before surgery.
Extraocular muscles are supported by an annular ring of connective tissue (pulley) located near the equator of the globe within Tenon’s capsule. The pulley is attached to the orbital wall, adjacent extraocular muscles, and the equatorial Tenon’s capsule by bands densely woven with collagen, elastin, and smooth muscle.
Each rectus muscle has two muscle layers.
The pulley bends the path of the rectus muscles and the inferior oblique muscle, similar to how the trochlea bends the path of the superior oblique tendon. Dense bands exist between adjacent pulleys.
The LR-SR band vertically supports the lateral rectus pulley against the downward force of the inferior oblique muscle, maintaining its position. With aging, this band degenerates, causing the lateral rectus pulley to shift downward (sagging) and the superior rectus to shift inward 1). When the lateral rectus sags downward, abduction function decreases, leading to esotropia 1).
Age-related distance esotropia
Bilateral symmetric degeneration: The LR pulley on both sides shifts symmetrically downward.
Distance esotropia: Due to reduced abduction, esotropia occurs during distance fixation, while orthophoria is maintained during near fixation.
Horizontal function preserved: The range of horizontal eye movements and saccade velocity remain normal.
Cycloverical Strabismus
Asymmetric degeneration: The downward shift of the LR pulley occurs asymmetrically between the left and right eyes.
Hypotropia + excyclotorsion: The eye on the more degenerated side shows hypotropia and excyclotorsion.
LR-SR band rupture: Ligament rupture is confirmed in 91% of CVS eyes.
It also differs from heavy eye syndrome on imaging; in heavy eye syndrome, the lateral rectus displacement is much larger, with nasal displacement of the superior rectus and superotemporal prolapse of the globe, but in sagging eye syndrome these findings are mild1).
A pulley is a ring-shaped connective tissue structure that controls the path of the extraocular muscles. It is located near the equator of the globe within Tenon’s capsule and is composed of collagen, elastin, and smooth muscle. The orbital layer of the rectus muscle inserts into the pulley, determining the direction of muscle action during eye movement.
