INTRODUCTION
Posterior Polymorphous Dystrophy (PPD) is a disease of the cornea endothelium which the clinical spectrum varied greatly, ranging from presence of posterior corneal vesicles to the formation of peripheral anterior synechiae and cornea edema. Patients can present asymptomatically as an incidental finding or with a certain degree of visual impairment (Teekhasaenee et al. 1991).
PPD also has been reported to be in association with other anterior segment abnormalities such as Iridocorneal Endothelium (ICE) Syndrome and keratoconus (Blair et al. 1992; Kiel 1999). Genetic mutation as the hypothesized pathogenesis of these association has also been studied, which revelaed similar changes in their molecular basis and lead to the characteristic corneal dystrophies (Heon et al. 2002).
We report a case of PPD in a child who presented with poor vision secondary to high astigmatism and amblyopia. This case is interesting since the age of presentation and presenting signs and symptoms were rather unusual. The degree of disease severity also did not correlate well with the typical keratoconus.
CASE REPORT
A 10-year-old girl with a family history of glaucoma presented with blurring of vision in the right eye for few years. Her best corrected vision was 6/9 for both eyes. Slit-lamp examination showed vesicular-like lesions at the level of Descemet membrane and endothelial layers of the cornea in both eyes (OU) (Figure 1). Intraocular pressure (IOP) was 12 and 13 mmHg for the right and left eye, respectively. Both optic discs were non-glaucomatous with cup-to-disc ratio (CDR) of 0.4. Other ocular examinations were unremarkable. Her mother was diagnosed to have glaucoma and underwent filtering surgery on the left eye.
Cycloplegic refraction revealed high astigmatism in the right eye (OD) with cylindrical power of -3.00 D, while the left eye (OS) was -0.50 D. Corneal topography showed normal regular astigmatism in OD but irregular astigmatism with paracentral coning suggestive of keratoconus in OS (Figure 2). Endothelial cell density was reduced in the OD (1745 cells/mm2) compared to the OS (2172 cells/mm2), with no features of polymegathism or pleomorphism (Figure 3).
Patient was diagnosed to have both eyes PPD with moderate amblyopia in the right eye. She was advised to patch the left eye for 2 hours/day and given follow-up with special attention on worsening of visual acuity, refraction, IOP and endothelial cell counts. Serial corneal topography was scheduled to monitor progressive steepening of cornea indicating risk of endothelial dysfunction. Her best corrected vision during follow-up period of 3 months improved to 6/7.5 and 6/6 for right and left eye, respectively
DISCUSSION
PPD is a rare autosomal dominant disorder where there are multi-layered endothelium appearing as vesicles, bands-, or diffuse opacities. Although majority of patients present during adulthood, the presentation age is highly variable due to the broad spectrum of disease severity (Raber et al. 2011). It is usually bilateral, asymptomatic, and non-progressive, with a variable degree of symmetry (Raber et al. 2011). In this case, the patient presented at the age of 10 years with asymmetrical degree of astigmatism, together with incidental findings of PPD which involve both corneas.
While PPD was described in association with keratoconus (Cremona et al. 2009), cases of patients with PPD with non-keratoconic corneas have been reported (Aldave et al. 2013). In these cases, steep corneal curvatures were seen but, no clinical or topographical evidence of keratoconus (Ahn et al. 2017). Interestingly, our patient had both features; keratoconic cornea on the left eye and paracentral vesicular lesions of PPD.
In children, abnormal development of corneal endothelium might affect corneal shape and refractive power, thus decreases their visual acuity (Derespinis et al. 1996). Asymmetric or unilateral involvement of the cornea might risk them to have anisometropic amblyopia associated with greater astigmatism (Derespinis et al. 1996). This is consistent with the findings in our patient where uncorrected asymmetrical astigmatism was detected on both eyes, thus treatment for amblyopia was prescribed which resulted in improvement of visual acuity.
In the present case, the patient was prescribed with patching regimen of her better eye for 2 hours/day and best corrected visual acuity was assessed to monitor for improvement. Both strabismic or anisometropic amblyopia would benefit from occlusion of the sound eye for as few as 2 hours/day, with an average of improvement reported as 0.9 lines compared to patients prescribed with optical corrective glasses (Wallace et al. 2006).
Although 25% of patients with PPD were reported to have peripheral iridocorneal adhesions, only 13% of them developed glaucoma, which explains the slowly progressive or non-progressive pathogenesis of PPD (Rodrigues et al. 1980). Gonioscopy and evaluation of optic disc and visual field should be performed to detect glaucoma, as well as screening of family members for glaucoma (Cibis et al. 1977). In the present case, the patient did not have glaucoma at this stage as she was still young but needs to be followed-up closely. A strong family history of glaucoma on the maternal side put her at risk of glaucoma.
Visual prognosis for patients with unilateral PPD may be related to the position of the lesions, age at diagnosis, severity of astigmatism, and early-childhood corrective spectacle use (Jeon & Hyon 2017). Therefore, practitioners should closely monitor patients with PPD for development of anisometropia and amblyopia. Majority of PPD patients may retain normal vision and remain symptom-free (Cibis et al. 1977), avoiding the need for corneal transplant.
Corneal transplant may be required at a later stage especially in eyes with keratometric value greater than 48.0D, as the degree of endothelial dysfunction is greater in eyes with pronounced corneal steepening (Aldave et al. 2013). This explains the importance of monitoring serial corneal topography in PPD cases. Keratoplasty in simultaneous corneal ectasia and PPD may be unavoidable, but clinician must first decide whether the indication is keratoconus or PPD or both. If the PPD lesions are away from visual axis and endothelial cell count is well over 2000, deep anterior lamellar keratoplasty may be the choice of treatment. Likewise, if the endothelial count is poor, performing penetrating keratoplasty may be the better option in such cases.
Essentially, PPD can present in children with high astigmatism and amblyopia. Careful examination of the corneal endothelium together with the refractive status should be performed in a child complaining of blurring of vision. Corneal topography is a useful adjunct in diagnosis of concurrent keratocnonus.
CONCLUSION
PPD can present at an early age and may be associated with high astigmatism which subsequently leads to amblyopia. Corneal topography helps to identify any early sign of keratoconus. Endothelial cell count should be evaluated during follow-up to anticipate cornea decompensation. Proper corneal evaluation aids in prognostication of the need for future corneal transplant and the type of surgery needed.