Categories
Ocular System

Pterygium

Wing-shaped fibrovascular overgrowth of bulbar conjunctiva across the limbus onto the cornea.

Introduction

Wing-shaped fibrovascular overgrowth of bulbar conjunctiva across the limbus onto the cornea.


Aetiology

Environmental exposure:

  • Sun exposure (UV rays) (M/C cause)
  • Hot, dry & dusty conditions (#2 M/C cause)

Pathophysiology

Limbal stem cells:

A healthy corneal surface is maintained by self-renewing, lineage-specific stem cells (SCs) that reside in the limbus, a narrow annular transition zone that circumscribes the cornea. This regenerative capacity is regulated by exquisite programs that govern stem cell quiescence, proliferation, migration, and differentiation. Failure to maintain a normal microenvironment as a result of extrinsic (eg, UV radiation) or intrinsic (eg, cytokines) signals can result in the development of ocular disorders.

UV rays cause the insufficiency of the limbal stem cells of the cornea. It causes activation of the tissue growth factors, which further lead to angiogenesis and cell proliferation. The limbal stem cells are damaged by the UV rays that cause conjunctivalization of the cornea, and the cornea is invaded by aggressive fibroblasts. UV radiation may cause mutations in the p53 tumor suppressor gene, resulting in the abnormal pterygial epithelium.

The role of cumulative UV radiation exposure in pterygium development. A: Model for the pathogenesis of pterygium: focal limbal damage from UV radiation triggers migration of altered LSCs toward the central cornea. B: In total LSC deficiency, damage to the limbal niche or depletion of stem cell reserves results in conjunctivalization of the cornea from all directions. C: Model of how ocular surface squamous neoplasia and melanoma might arise from pterygia. Question marks with pathways indicate absence of direct supporting clinical or experimental evidence. D: Bisection and orientation of pterygium specimens as assessed in the current study. | Chui, J., Coroneo, M. T., Tat, L. T., Crouch, R., Wakefield, D., & Di Girolamo, N. (2011). Ophthalmic pterygium: a stem cell disorder with premalignant features. The American journal of pathology, 178(2), 817–827. https://doi.org/10.1016/j.ajpath.2010.10.037

Recurrent pterygium:

Reactivation of inflammatory process: Proliferative cytokines and growth factors (including VEGF) can increase after surgery if limbal stem cells remain activated, and fibroelastic tissue is also involved. Because of this, there is an acceleration of fibrovascular proliferation and an increase in metalloproteinase synthesis that destroys the Bowman membrane and the stromal collagen that may increase the progress of pterygium.

Histopathology:

Microscopically, pterygium is considered to be composed of elastotic fibro-vascular tissue. Leaving the top, mostly, the pterygium is covered by conjunctival epithelium. Extensions of fibrous tissue are seen on the top of pterygium, and as the head encroaches on to the cornea, the Bowman’s layer gets involved and is fragmented. The fibrous connective tissue fills these cavities.
  • Hyperplastic, centripetally directed growth of altered limbal epithelial cells
  • Bowman’s layer dissolution
  • Epithelial-mesenchymal transition
  • Activated fibroblastic stroma with inflammation, neovascularization, and matrix remodeling, mediated through the concerted actions of cytokines, growth factors, and matrix metalloproteinases
Typical histological features of pterygia. A: In the advancing head of a pterygium, conjunctival-like epithelium (Conj) merges abruptly into corneal epithelium (Corn). The underlying Bowman’s layer (arrows) is fragmented and precedes a fibrovascular stroma (asterisk). B, C: Goblet cell hyperplasia is apparent in pterygium (B), compared with donor-matched conjunctiva (C). Note the thickness of the epithelial layer (double-headed arrows in B and C). D: Prominent central feeder vessel; inset shows dilated subepithelial vessels. E: Elastotic changes (double asterisk) in pterygium stroma. F: Inflammatory infiltrates in the epithelium. G: Stromal vessels loaded with polymorphonuclear leukocytes. All sections were stained with H&E. Original magnification: ×200 (A and D); ×400 (B, C, D inset, and E); ×1000 oil emersion (F and G). | Chui, J., Coroneo, M. T., Tat, L. T., Crouch, R., Wakefield, D., & Di Girolamo, N. (2011). Ophthalmic pterygium: a stem cell disorder with premalignant features. The American journal of pathology, 178(2), 817–827. https://doi.org/10.1016/j.ajpath.2010.10.037

Clinical features

  • Irritation in the eye
  • Lacrimation
  • Foreign body sensation
  • Cosmetic blemish
  • Defective vision
  • Diplopia
(A) Nasal bilateral pterygium. (B and C) The extent of advancement of the lesions on the corneal surface of the right and left eye is shown on abduction. | Chalkia K., A., Spandidos A., D., & Detorakis T., E. (2013). Viral involvement in the pathogenesis and clinical features of ophthalmic pterygium (Review). Int J Mol Med, 32(3), 539–543. https://doi.org/10.3892/ijmm.2013.1438

Pterygium description:

Triangular fold of conjunctiva encroaching the eye
  • Morphology:
    • Cap: At the leading edge, distinguished by a halo-like avascular zone
    • Head: Peripheral to the cap
    • Body: Main part of pterygium communicating with bulbar conjunctiva
  • Types:
    • Progressive type: Thick, fleshy, vascular, progressively encroaching towards the center of the cornea. “Fuck’s spots or Islets of Vogt”
    • Atrophic type: Thin, attenuated, poor vascularity, stationary
    • Regressive type:”Stocker’s line” (line of iron deposition)
Clinical appearance of Fuchs’ flecks in pterygia. A: Original illustrations by Ernst Fuchs show small spots or fleckchen in the cap region at the head of pterygia. B–E: Pterygia with Fuchs’ flecks (arrows) under slit lamp (B and C) and in vivo confocal microscopy (D and E). | A: Fuchs E. Ueber der Pterygium. Graefes Archiv Ophthalmol 1892, 38:1–89). | B-E: Chui, J., Coroneo, M. T., Tat, L. T., Crouch, R., Wakefield, D., & Di Girolamo, N. (2011). Ophthalmic pterygium: a stem cell disorder with premalignant features. The American journal of pathology, 178(2), 817–827. https://doi.org/10.1016/j.ajpath.2010.10.037

Diagnosis

Differential diagnosis:

  • Pseudopterygium: Fold of bulbar conjunctiva attached to cornea
 PterygiumPseudopterygium
EtiologyDegenerative processInflammatory process
AgeElderlyAny age
SiteAlways in palpebral apertureAny site
StagesProgressive, regressive, stationaryAlways stationary
Probe testCannot be passed underneathCan be passed under the neck

Management

Medical management:

Medical care is given to relieve the patient from the inflammatory symptoms and reduce the persistent discomfort that persists.
  • Lubrication with artificial tear drops or decongestants
  • Topical NSAIDs
  • Eye drop loteprednol
  • Vasoconstrictive agents minimize redness and enhance the appearance and add antihistamines to the decongestant drops to help prevent the effect of histamine associated edema and itching.

Surgical management:

Reasons for surgery are decreased vision due to visual axis encroachment, chronic pain, persistent inflammation, abnormal astigmatism, restrictive ocular motility, and cosmesis.

Leave a Reply