Corneal Dystrophy

BASICS


DESCRIPTION


• Macular corneal dystrophy (Groenouw corneal dystrophy Type II, Fehr spotted dystrophy) is an autosomal recessive, progressive, bilateral, noninflammatory condition characterized by multiple opacifications with intervening haze within the corneal stroma.


• Patients present with corneal clouding by ages 3–9 years.


• Opacities are focal, gray-white, ill-defined, and extend to the peripheral cornea. They can present throughout the entire thickness of the stroma and, in advanced cases, extend to Descemet’s membrane and the endothelium producing guttae excrescences and corneal edema. The opacities are typically superficial centrally and more posterior peripherally.


• Compared to other corneal stromal dystrophies (granular and lattice), macular corneal dystrophy is:


– the least common


– has reduced vision at an earlier age


– has thinner central corneal thickness in the early stages of the disease


– has no clear areas between opacities


– extends to the peripheral cornea


– requires corneal transplantation at an earlier age


– has the lowest frequency for corneal transplant replacement; however, recurrence of the opacities from macular dystrophy can still occur in the transplant (1).


• Symptoms include: progressive vision loss (usually severe by second to third decade), glare, photophobia, recurrent erosions.


EPIDEMIOLOGY


Incidence/Prevalence


Uncommon, no reports in literature


RISK FACTORS


Consanguinity (2)


Genetics


• Autosomal Recessive


• Genetic locus: 16q22


• Gene: Carbohydrate sulfotransferase 6 gene—CHST6 (3,4)


PATHOPHYSIOLOGY


• The opacities are glycosaminoglycans (GAGs or mucopolysaccharides) that accumulate intracellularly and extracellularly in the corneal stroma, Descemet’s membrane, and endothelium.


• In macular corneal dystrophy, GAGs accumulate in the endoplasmic reticulum of cells, whereas in systemic mucopolysaccharidoses, GAGs accumulate in lysosomal vacuoles.


• GAGs stain with Alcian blue, Hale colloidal iron, metachromatic dyes, and Periodic Acid-Schiff (PAS).


• Electron microscopy shows that the GAGs stain positively in keratocytes and endothelial cells. They also stain positively in the extracellular matrix fibrillogranular material.


ETIOLOGY


• Autosomal recessive, progressive, bilateral, noninflammatory condition characterized by multiple opacifications with intervening haze within the corneal stroma.


• The opacities are glycosaminoglycans (GAGs or mucopolysaccharides) with corneal clouding by ages 3–9 years.


DIAGNOSIS


HISTORY


• Macular corneal dystrophy is an autosomal recessive, progressive, bilateral, noninflammatory condition characterized by multiple opacifications with intervening haze within the corneal stroma.


• Presents with corneal clouding by ages 3–9 years


• Symptoms include: Progressive vision loss (usually severe by the second to third decade), glare, photophobia, recurrent erosions.


• Possible history for consanguinity in parents


PHYSICAL EXAM


• Full ophthalmic examination including measurement of intraocular pressure and dilated fundus examination


• B-Scan ultrasound to rule out posterior segment pathology if unable to visualize secondary to corneal opacification


• Ultrasound pachymetry to measure central corneal thickness


• Specular microscopy to measure endothelial cell counts if possible


• Slit-lamp examination shows:


– Focal, gray-white opacities that are ill-defined and extend to the peripheral cornea


– Opacities can present throughout the entire thickness of the stroma and, in advanced cases, extend to Descemet’s membrane and the endothelium, producing guttae excrescences and corneal edema.


– The opacities are typically superficial centrally and more posterior peripherally.


– There are no clear areas between opacities.


– Opacities extend to the peripheral cornea.


DIAGNOSTIC TESTS & INTERPRETATION


Lab


Initial lab tests

ELISA may be used to measure sulfated keratan sulfate.


Follow-up & special considerations

• Slit-lamp examination


• Ultrasound pachymetry


• Specular microscopy


Pathological Findings


• The opacities are glycosaminoglycans (GAGs, mucopolysaccharides) that accumulate intra- and extracellularly in the corneal stroma, Descemet’s membrane, and endothelium.


• In macular corneal dystrophy, GAGs accumulate in the endoplasmic reticulum of cells, whereas in systemic mucopolysaccharidoses, GAGs accumulate in lysosomal vacuoles.


• GAGs stain with Alcian blue, Hale colloidal iron, metachromatic dyes, and PAS.


• Electron microscopy shows that the GAGs stain positively in keratocytes and endothelial cells. They also stain positively in the extracellular matrix fibrillogranular material.


• Immunoreactivity of an antibody specific for sulfate epitopes on antigenic keratan sulfate (AgKS) delineates the three variants of macular corneal dystrophy. Clinical presentation is similar between the three types (2)


– Type 1


– AgKS nonreactive to cornea and serum


– Type 1 A


– AgKS reactive to keratocytes


– AgKS nonreactive to extracellular matrix and serum


– Type 2


AgKS reactive to cornea and serum


DIFFERENTIAL DIAGNOSIS


• Granular corneal dystrophy


• Schnyder’s crystalline corneal dystrophy (SCCD)


• Avellino corneal dystrophy


• Lattice corneal dystrophy


TREATMENT


MEDICATION


• Artificial tears for recurrent erosions. No contraindications.


• Topical hypertonic saline (5%) drops (1 drop q.i.d) and ointment (q.h.s). No contraindications.


ADDITIONAL TREATMENT


General Measures


• Tinted contact lenses to reduce photophobia


• Pressure patch of eye to allow healing of epithelial defect


• Therapeutic contact lenses for recurrent corneal erosions with topical antibiotic coverage (1 drop q.i.d.)


• Risks of corneal infection possible with patching and contact lens use. Patient requires frequent follow-up until healed.


Issues for Referral


• Worsening vision


• Nonhealing epithelial defects


SURGERY/OTHER PROCEDURES


• Phototherapeutic keratectomy (PTK):


– Early onset disease with anterior stromal opacities


– Treatment of recurrent erosions (5)


• Keratoplasty (corneal transplantation) for more posterior stromal opacities leading to significant visual loss


– Lamellar keratoplasty (LK)


– Deep anterior lamellar keratoplasty (DALK)


– In cases without opacities in Descemet’s membrane or endothelium


– DALK has a reduced risk of endothelial rejection of the corneal transplant


– Full-thickness penetrating keratoplasty (PKP)


IN-PATIENT CONSIDERATIONS


Discharge Criteria


• Risks of corneal infection possible with patching and contact lens use


• Patients with recurrent erosions should be followed closely until the epithelial defect has healed.


ONGOING CARE


FOLLOW-UP RECOMMENDATIONS


Periodic follow-up to monitor status of opacities and vision


Patient Monitoring


• Timing of outpatient follow-up is dependent on severity of disease.


– Patients who are stable can be followed every 6–12 months.


– Patients with recurrent erosions should be followed every 1–7 days, until healed.


– Patients with pressure patch should be seen every 24–48 hours.


PATIENT EDUCATION


• Patients should be advised to seek medical attention immediately if there are any symptoms of pain, acute visual loss, redness, purulent discharge, or severe photophobia.


• As the disease is progressive, patients may be advised a surgical procedure (PTK or corneal transplantation) if there is significant visual loss.


PROGNOSIS


Patients have progressive vision loss (usually severe by second to third decade), glare, photophobia, and recurrent erosions.


COMPLICATIONS


• Progressive vision loss with glare, photophobia, and recurrent erosions


• Despite successful treatment with PTK and/or corneal transplantation, recurrences can still occur.



REFERENCES


1. Marcon AS, Cohen EJ, Rapuano CJ, Laibson PR. Recurrence of corneal stromal dystrophies after penetrating keratoplasty. Cornea 2003;22:19–21.


2. Pandrowala H, Bansal A, Vemuganti GK, Rao GN. Frequency, distribution, and outcome of keratoplasty for corneal dystrophies at a tertiary eye care center in South India. Cornea 2004;23:541–546.


3. Weiss JS, Moller HU, Lisch W, et al. The IC3D classification of the corneal dystrophies. Cornea 2008;27(Suppl 2):S19–S20.


4. Klintworth GK, Smith CF, Bowling BL. CHST6 mutations in North American subjects with macular corneal dystrophy: A comprehensive molecular genetic review. Mol Vis 2006;12:159–176.


5. Szentmáry N, Seitz B, Langenbucher A, et al. Histologic and ultrastructural changes in corneas with granular and macular dystrophy after excimer laser phototherapeutic keratectomy. Cornea 2006;25:257–263.

Only gold members can continue reading. Log In or Register to continue

Nov 9, 2016 | Posted by in OPHTHALMOLOGY | Comments Off on Corneal Dystrophy
Premium Wordpress Themes by UFO Themes