Haws syndrome in cats

Introduction

Haws syndrome is a distinctive neuro-ophthalmic condition of cats, defined by bilateral protrusion of the third eyelids (nictitating membranes) and ptosis (droopy upper eyelids) in the absence of ocular pain, miosis or enophthalmos (Figure 1) (1). Although the clinical appearance is striking, the condition is benign, self-limiting, and does not threaten vision. For many years the syndrome was regarded as idiopathic, but recent findings suggest a link between gastrointestinal disease, microbial imbalance, and transient dysfunction of ocular sympathetic innervation (1,2). This evolving understanding places haws syndrome within the broader framework of the gut-brain-eye axis, in which gastrointestinal health influences ocular and neurologic function. This article summarizes the historical background of the syndrome, outlines its clinical and epidemiologic features, discusses proposed mechanisms, and provides a practical approach to diagnosis and management.

Figure 1. Haws syndrome in an 8-month-old male Domestic Shorthair cat.

© Modified with permission from (2).

 

Historical background

Haws syndrome was first recognized in 1977, when young cats – often living in multicat households – were described as having acute, bilateral elevation of the third eyelids, which typically recovered spontaneously over a period of weeks to months (3,4). Subsequent work focused on a potential viral etiology. A UK clinical and microbiological study in 1990 examined cats with protruding nictitating membranes and diarrhea, and reported a hemagglutinating torovirus-like agent in feces from many affected animals, proposing an association with the syndrome (5). However, a later survey from New Zealand analyzed fecal samples from 51 cats (cases with haws syndrome, historical cases, and controls) and failed to detect torovirus or torovirus-like particles in any group, concluding that their data did not support a torovirus-associated syndrome (6). Together, these studies suggest that if an infectious agent is involved, it may differ between populations or regions.

Additional cases from South America have broadened the clinical spectrum. One study from 2014 described three cases of haws syndrome in young cats, with or without diarrhea, and highlighted the benign, self-limiting course (7). Another study reported a detailed case with bilateral third eyelid elevation that was responsive to topical phenylephrine, consistent with a transient sympathetic disturbance (8). Other reports have linked the syndrome to giardiasis, with bilateral third eyelid elevation occurring alongside soft feces or diarrhea and resolving after treatment of enteritis (9,10). 

These geographically diverse observations, now complemented by recent clinicopathologic studies (1,2), support a consistent view of haws syndrome as being a benign, self-limiting autonomic disorder in young cats, most likely triggered by one or more contagious gastrointestinal pathogens rather than a single, universal etiologic agent.

Clinical presentation and epidemiology

A recent prospective study provided the most comprehensive clinical characterization of haws syndrome to date (1). Ten cats, all under three years of age (mean ≈ 1.5 years), presented with the following consistent features: 

(i) bilateral, symmetrical elevation of the third eyelids; 

(ii) ptosis of the upper eyelids; 

(iii) normal pupil size and responsiveness; 

(iv) normal globe position without enophthalmos; and 

(v) absence of ocular pain, photophobia, or inflammation.

 

Diarrhea was observed in approximately half the cats, and Giardia duodenalis was identified in several cases. In one household, a newly adopted kitten with diarrhea was diagnosed with haws syndrome, and three resident cats then developed identical signs within 4–11 days, indicating horizontal transmission of a presumed gastrointestinal pathogen (1). Routine hematologic and biochemical parameters were within reference ranges, and serum amyloid A concentrations were normal or minimally elevated, suggesting minimal or no systemic inflammation. Clinical signs resolved spontaneously in all but one cat, typically within 12 to 95 days (mean ≈ 5 weeks). Recurrence occurred in about one-third of cases within six months. Throughout, affected cats remained bright, active, and normorexic, confirming the benign nature of the condition (1).

A later case series assessed dietary management, whereby five cats were transitioned to a gastrointestinal diet without additional medical therapy, with all recovering within 11—39 days (mean ≈ 3.5 weeks), and none relapsed during a one-year follow-up (2). This response supports an underlying gastrointestinal component and a role for nutritional modulation of intestinal health in disease resolution.

Etiopathogenesis

Gastrointestinal disturbance and dysbiosis

The most consistent features across studies include gastrointestinal signs, detection of enteric pathogens in some cases, and frequent occurrence in multicat environments. Together, these findings suggest that haws syndrome represents a neuro-ophthalmic response to gastrointestinal disturbance, rather than a primary ocular disease. While various infectious agents have been detected – ranging from enteric viruses to Giardia duodenalis – none has been universally present. The syndrome may therefore result from diverse gastrointestinal insults that converge on a common mechanism: inflammation-induced alteration of the gut microbiome and subsequent disruption of neural communication along the gut–brain axis.

The negative results reported in torovirus testing (6) reinforce the likelihood that multiple, regionally variable pathogens or dysbiosis patterns can precipitate the same autonomic outcome. This ecological model fits with the variability of reported triggers and the self-limiting course of the condition.

Ocular sympathetic dysfunction

The clinical and pharmacologic features of haws syndrome suggest a partial, postganglionic, sympathetic neuropathy. The third eyelid and upper eyelid receive sympathetic input from the superior cervical ganglion; loss of this tone produces elevation of the third eyelid and ptosis. Topical 1% phenylephrine or 0.05% tetrahydrozoline typically induces rapid, temporary resolution of both signs, confirming adrenergic receptor hypersensitivity secondary to denervation (1).

A notable feature of haws syndrome is the absence of miosis, distinguishing it from classical Horner’s syndrome. This selective dysfunction – affecting sympathetic fibers to the third and upper eyelids but sparing those to the iris dilator – resembles some cases of “atypical Horner’s” as described in humans, where partial sympathetic lesions cause ptosis without miosis (or vice versa) (11). The mechanism remains uncertain, but may involve low-grade neuroinflammation or altered gut–brain signaling that transiently impairs specific neurons within the superior cervical ganglion or modifies receptor sensitivity through circulating microbial metabolites.

The gut–brain–eye axis

Experimental and clinical evidence supports a link between the intestinal microbiome and ocular physiology (12,13). The gut–brain axis describes bidirectional communication between the intestinal microbiota and the nervous system via neural, endocrine and immune pathways. Alterations in the gut microbiota can modify autonomic tone, and conversely, interruption of sympathetic outflow alters microbial composition (14).

Expanding this concept, the gut–eye axis recognizes the influence of gut dysbiosis on ocular homeostasis. Dysbiosis has been implicated in uveitis, dry eye disease, glaucoma, and age-related macular degeneration (12,13). Potential mechanisms include immune cross-reactivity, inflammatory mediator release, and microbial metabolites influencing vascular and neural regulation (15,16). Within this framework, haws syndrome can be viewed as a transient, reversible manifestation of gut-eye axis disruption, in which gastrointestinal imbalance perturbs ocular sympathetic control without structural ocular pathology.

Diagnosis

In most cases, diagnosis can be made confidently based on history and clinical pattern alone. However, third eyelid elevation is a common but non-specific clinical sign, so differentiation from other causes is essential. Differential diagnosis includes;

• Horner’s syndrome; typically presents unilaterally with miosis, ptosis and enophthalmos. Causes include otitis media, nasopharyngeal polyps, or cervical trauma (17). In contrast, haws syndrome is bilateral, pupils are normal, and the globe is in a normal position.
• Feline dysautonomia (Key-Gaskell syndrome); causes diffuse autonomic failure, with third eyelid elevation, mydriasis, dry nose, constipation, and urinary retention (18). Affected cats are systemically ill and have a poor prognosis, unlike those with haws syndrome.
• Ocular pain; uveitis, keratitis, or glaucoma pain can cause reflex third eyelid elevation, but such eyes show blepharospasm, photophobia, and corneal or anterior chamber changes (19).
• Orbital disease (abscess, cellulitis, neoplasia) or enophthalmos from dehydration or cachexia; these conditions may elevate the third eyelid but will be accompanied by systemic or structural abnormalities.
• Third eyelid gland prolapse (“cherry eye”); appears as a pink, irregular mass rather than smooth, symmetrical elevation.

 

Recognizing the clinical pattern of haws syndrome avoids unnecessary diagnostics and ensures appropriate management.

Diagnosis is clinical and based on the characteristic appearance of bilateral third eyelid elevation and ptosis in an otherwise healthy cat with normal pupils and a quiet ocular surface. A complete ophthalmic examination, including tear testing, fluorescein staining and tonometry, is essential to exclude ocular pain or corneal disease. The phenylephrine test is helpful diagnostically: application of 1% phenylephrine normalizes third eyelid position within 5–20 minutes, confirming postganglionic sympathetic dysfunction (Figure 2).

Baseline bloodwork and fecal testing (including Giardia antigen) are recommended, particularly in cats with diarrhea or when multiple cats are affected. Serum amyloid A may help confirm the absence of systemic inflammation. Advanced imaging is reserved for atypical presentations (e.g., unilateral involvement, miosis, neurological deficits or orbital changes).

Figure 2. Haws syndrome in a 2-year-old male Domestic Shorthair cat (a). Note the rapid, transient resolution of third-eyelid elevation and ptosis within 7 minutes after topical administration of 1% phenylephrine in the left eye (b).

© Modified with permission from (1).

 

Management and prognosis

General considerations

Because haws syndrome is self-limiting, management should be supportive. Empirical antibiotic or antiparasitic therapy may be indicated in specific cases, but rarely shortens the duration of disease. The therapeutic focus should be on gastrointestinal stabilization and avoidance of unnecessary interventions that could worsen dysbiosis. Topical ophthalmic therapy is not required, as the ocular surface is unaffected. Phenylephrine or tetrahydrozoline may be used for temporary cosmetic improvement, but has no impact on recovery.

Dietary management

Evidence from clinical series supports dietary management as a practical and effective approach (2,20). Transitioning affected cats to a gastrointestinal diet, formulated for high digestibility and optimal intestinal health, has been associated with faster resolution and reduced recurrence (Figure 3). In a recent case series, cats fed exclusively a gastrointestinal diet for three months all recovered from haws syndrome within six weeks and remained relapse-free for at least one year (2). The mechanism is presumed to involve normalization of gut microbiota and restoration of homeostatic signaling along the gut-brain-eye axis (20). Studies in companion animals show that dietary changes can modify intestinal microbial composition within days, reducing inflammation and improving systemic immune balance (21,22). However, owners should be advised that improvement may take several weeks, and continued feeding of a gastrointestinal diet for several months after recovery appears to minimize relapse risk.

Figure 3. Haws syndrome in two male Domestic Shorthair cats; a 2.5-year-old cat (upper) and a 3-year-old cat (lower), shown before (left) and after (right) initiation of a gastrointestinal diet.

© Modified with permission from (1).

 

Prognosis

The prognosis for haws syndrome is excellent. The condition is non-painful, does not impair vision, and resolves spontaneously or with supportive management within weeks to months. Recurrence is uncommon once gastrointestinal health is stabilized, but owner education is important to prevent overtreatment and anxiety. Explaining the benign nature of the condition, expected duration, and relationship to intestinal health reassures owners and encourages adherence to dietary recommendations.

Future directions

Although clinical recognition of haws syndrome is straightforward, its underlying pathophysiology remains incompletely understood. Key questions include: 

(i) Which specific enteric pathogens or microbiome alterations trigger the condition? 

(ii) How do gut-derived immune or neurochemical signals selectively impair sympathetic neurons supplying the third and upper eyelids? and 

(iii) Can microbiome-targeted therapies, such as specific diets or probiotics, reduce disease duration or prevent recurrence? Future work integrating metagenomic, metabolomic and neurophysiologic analyses may clarify these mechanisms and further establish haws syndrome as a model for gut–eye communication in companion animals.

Conclusion

Haws syndrome exemplifies the complex interaction between the gastrointestinal system and ocular autonomic function. Once considered idiopathic, it is now increasingly viewed as a transient, reversible sympathetic neuropathy linked to gastrointestinal disease and dysbiosis. Recognition of its characteristic presentation and benign course enables veterinarians to manage affected cats conservatively, emphasizing intestinal health and nutritional support rather than pharmacologic intervention. By restoring balance in the gut, clinicians often restore balance in the eye, a concept that continues to refine our understanding of ocular disease in cats.

References

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