Eye Findings in Cystinosis
Cystinosis causes characteristic corneal cystine crystal deposition beginning in infancy, progressing to photophobia, visual impairment, and retinopathy, requiring lifelong topical cysteamine therapy and multidisciplinary ophthalmologic surveillance.
Primary Ocular Manifestations
Corneal Findings
The hallmark ocular finding is cystine crystal accumulation throughout all corneal layers, which begins asymptomatically in the first years of life and progresses predictably 1. Crystals initially appear in the peripheral corneal epithelium during infancy, then evolve toward the corneal depth and center during the second decade of life 2. By age 10-15 years, crystal deposition becomes severe enough to cause significant symptoms 2.
Corneal thickness is characteristically elevated (median central corneal thickness 579 µm), though peripheral corneal thickness and keratometry remain largely normal 3. Importantly, despite crystal accumulation, frank corneal edema does not typically occur 3.
Visual Symptoms and Function
- Photophobia is the most debilitating symptom, generally beginning by age 10 but becoming severe after age 15 2
- Visual acuity often remains preserved (mean logMAR 0.08) despite extensive crystal deposition 3
- Contrast sensitivity is frequently reduced even when visual acuity appears normal 3
- Corneal sensation progressively declines toward low measurable values, representing one of the most consistent longitudinal changes 3
Retinal Involvement
Retinopathy occurs in approximately 50% of patients 2. Findings include:
- Peripheral retinal pigmentary changes
- Maculopathy (less common)
- Intraretinal hyperreflective dots on OCT consistent with crystalline deposits 3
- Increased central macular thickness (means 280-305 µm) 3
- Electroretinogram flattening in some cases 2
The severity of retinopathy has decreased with modern oral cysteamine therapy, which reaches retinal vasculature and reduces crystal accumulation 2.
Additional Ocular Findings
- Conjunctival crystals present in most patients 3
- Tear hyperosmolarity occurs frequently despite normal Schirmer testing 3
- Band keratopathy (in advanced cases) 1
Recommended Management
Topical Cysteamine Therapy
Topical cysteamine 0.55% (Cystadrops®) is the only therapy that reduces corneal crystal accumulation and must be initiated as soon as corneal crystals are apparent 4, 5. Treatment should begin in infancy (as early as 6 months of age when crystals first appear) rather than waiting for symptoms to develop 5.
- Dosing: Every 2 hours while awake
- Efficacy: Reduces or stabilizes corneal crystal scores and photophobia even in infants at a stage when progression would otherwise be expected 5
- Adherence is critical for long-term outcomes 4
Systemic Cysteamine
Oral cysteamine therapy addresses systemic disease and appears to reduce retinal crystal accumulation by reaching retinal vasculature 2. This has improved the retinopathy prognosis compared to historical cohorts 2.
Structured Ophthalmologic Surveillance
A standardized ophthalmologic assessment protocol should include 6:
At diagnosis:
- Complete history focusing on photophobia and visual symptoms
- Best-corrected visual acuity
- Contrast sensitivity testing (Pelli-Robson)
- Tonometry
- Corneal sensation testing
- Slit-lamp examination with crystal grading
- Fundus photography
- Anterior segment imaging (confocal microscopy preferred; anterior segment OCT as alternative)
- Macular OCT and optic nerve imaging
Ongoing surveillance:
- Annual comprehensive examinations as above
- More frequent visits if complications develop
- Monitor for progressive corneal hypoesthesia 3
- Assess tear osmolarity and dry eye symptoms 3
Management of Inflammatory Component
As patients age, inflammation becomes increasingly significant in disease progression 4. The inflammatory component requires recognition and treatment, though specific anti-inflammatory protocols for cystinosis are not well-established in the literature 4. Consider topical corticosteroids when inflammation is evident, following principles similar to other corneal inflammatory conditions 7, 8.
Surgical Considerations
- Corneal transplantation may be necessary for severe cases with vision-threatening corneal infiltration after age 15 2
- Phototherapeutic keratectomy for superficial deposits
- Rigid gas-permeable contact lenses can improve visual function by creating a smoother refractive surface 1
Critical Pitfalls to Avoid
Delaying topical cysteamine initiation: Treatment must begin when crystals first appear in infancy, not when symptoms develop 5
Assuming normal visual acuity means adequate vision: Contrast sensitivity and glare disability may be severely impaired despite 20/40 or better acuity 1, 3
Overlooking progressive corneal hypoesthesia: This represents neurotrophic changes requiring monitoring and protective measures 3
Inadequate transition planning: As a lifelong condition requiring multidisciplinary care, structured transition from pediatric to adult ophthalmology is essential 9, 10
Focusing only on corneal disease: Retinopathy, though less common with modern therapy, still occurs in ~50% of patients and requires posterior segment surveillance 2