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Ocular System

Keratoconus (KCN)

Progressive bilateral corneal ectatic disorder with characteristic cone-like steepening of the cornea associated with irregular stromal thinning, resulting in a cone-like bulge (protrusion) and significant loss of vision.

Progressive bilateral corneal ectatic disorder with characteristic cone-like steepening of the cornea associated with irregular stromal thinning, resulting in a cone-like bulge (protrusion) and significant loss of vision.

Etiology

Risk factors:

  • Rigid gas permeable (RGP) contact lens wear
  • Chronic eye rubbing
  • Down syndrome
  • Atopic disease
  • Leber congenital amaurosis
  • Connective tissue disease
  • Tapetoretinal degeneration
  • Family history

Presentation

Initial presentation typically occurs during adolescence followed by 10–20 years of progression before a stable phase is reached in the third or fourth decade of life. In general, the progression of KC is very heterogeneous but ultimately 15–20% of patients will require a corneal transplant.

  • Significant and variable reduction in visual acuity ((having to change glasses frequently due to changes in refractive error)
  • Image distortion
  • Increased sensitivity to glare & light

Significant asymmetry reduces the ability of spherocylindrical spectacle lenses to adequately correct vision.

Diagnosis

KC should be suspected in patients with higher degrees of astigmatism, astigmatism with oblique axis, as well as when progression in astigmatism and/or spherical refraction occurs. Steep corneal curvature and a lack of 20/20 visual acuity in a non-amblyopic eye with optimal refraction, should also raise suspicion.

Slit lamp examination:

Absence of slit lamp signs of KC does not exclude absence of the disease
  • Stromal thinning at cone apex
  • Munson’s sign: V-shaped conformation of the lower eyelid produced by the ectatic cornea in downgaze
  • Paracentral stromal scars
  • Fleischer’s ring: iron deposits partially/completely surrounding the corneal cone
  • Vogt’s striae: Fine vertical lines in deep stroma and Descemet’s membrane that parallel the axis of the cone
  • Rizzuti’s sign: Conical reflection on the nasal cornea when a penlight is shone from the temporal side
  • Corneal hydrops (severe cases): Breaks in Descemet’s membrane with stromal permeation of aqueous through these breaks
Slit lamp images of KC signs
Slit lamp images of KC signs. A: Corneal thinning at the apex of the cone. B: Corneal ectasia, with indentation of the inferior eyelid upon down gazing C: Paracentral stromal scars. D: Fleischer’s ring, a pigmented, often incomplete line of iron deposits running around the base of the cone. E: Vogt’s stria: fine vertical lines, which are breaks in the deep stroma and Descemet’s membrane. F: Corneal hydrops, the most acute presentation of KC. Diffuse stromal opacity and edema, caused by breaks in the Descemet’s membrane leading to influx of fluid in the stroma. | Sharif, R., Bak-Nielsen, S., Hjortdal, J., & Karamichos, D. (2018). Pathogenesis of Keratoconus: The intriguing therapeutic potential of Prolactin-inducible protein. Progress in retinal and eye research, 67, 150–167. https://doi.org/10.1016/j.preteyeres.2018.05.002

Retinoscopy:

  • Irregular myopic astigmatism
  • Scissoring reflex
  • Charleux sign: “Oil-droplet” reflex

Anterior segment optical coherence tomography (OCT):

3D re-creation of the anterior segment including: anterior and posterior cornea surfaces, corneal thickness analysis, anterior iris and len
Anterior cross-section Optical Coherence Tomography (OCT)
Anterior cross-section Optical Coherence Tomography (OCT). A1 and B1 show the scan location on the cornea. A2 and B2 show the cross-section view of the cornea. A: Healthy cornea. B: Severe KC cornea, characteristic protrusion and thinning as well as scarring at the top of the cone. | Sharif, R., Bak-Nielsen, S., Hjortdal, J., & Karamichos, D. (2018). Pathogenesis of Keratoconus: The intriguing therapeutic potential of Prolactin-inducible protein. Progress in retinal and eye research, 67, 150–167. https://doi.org/10.1016/j.preteyeres.2018.05.002

Corneal topography:

Restricted to measuring only the anterior corneal surface
Four image tomography map from Pentacam® HR
Four image tomography map from Pentacam® HR. A: Healthy cornea B: KC with severe ectasia and thinning, sagittal curvature (upper right), anterior elevation subtraction maps (upper left), corneal thickness (lower right) and posterior elevation subtraction map (lower left) are shown. | Sharif, R., Bak-Nielsen, S., Hjortdal, J., & Karamichos, D. (2018). Pathogenesis of Keratoconus: The intriguing therapeutic potential of Prolactin-inducible protein. Progress in retinal and eye research, 67, 150–167. https://doi.org/10.1016/j.preteyeres.2018.05.002

Keratometry:

  • Manual keratometry: Steep cornea, high astigmatism, and/or distorted mires in keratoconus
  • Computerized videokeratography: Zone of increased corneal power surrounded by zones of decreasing corneal power, inferior-superior asymmetry in corneal power, and skewing of the steepest radial axes above and below the horizontal meridian

Management

The treatment of KC depends on the severity and the rate of progression.

Keratoconus treatment algorithm
Keratoconus treatment algorithm. | VA visual acuity, RGP rigid gas-permeable lens, DALK deep anterior lamellar keratoplasty, PK penetrating keratoplasty, CL contact lens, Sp spectacle, CXL cornea cross-linking, PRK photorefractive keratectomy, RLE refractive lens exchange | Andreanos, K. D., Hashemi, K., Petrelli, M., Droutsas, K., Georgalas, I., & Kymionis, G. D. (2017). Keratoconus Treatment Algorithm. Ophthalmology and therapy, 6(2), 245–262. https://doi.org/10.1007/s40123-017-0099-1

Spectacles (initial treatment):

With progressive disease spectacles rapidly become insufficient.

Contact lenses:

Right choice and correct fitting contact lenses can often provide good visual acuity in the early stages before central scarring
  • Rigid Gas-Permeable (RGP) contact lenses (M/C)
  • Hybrid contact lenses (rigid center and a softer periphery)
  • Scleral contact lenses
  • Soft contact lenses designed specifically for KC
Contact lenses and Intra-corneal ring segments (ICRS)
Contact lenses and Intra-corneal ring segments (ICRS). A: Rigid-gas permeable lens B: Hybrid lens with rigid center and soft periphery. Notice transition between rigid and soft (arrow) C: Scleral contact lens. D: Lenses A-C out of eye. E: ICRS. Notice deposit on inner arc (arrow). | Sharif, R., Bak-Nielsen, S., Hjortdal, J., & Karamichos, D. (2018). Pathogenesis of Keratoconus: The intriguing therapeutic potential of Prolactin-inducible protein. Progress in retinal and eye research, 67, 150–167. https://doi.org/10.1016/j.preteyeres.2018.05.002

Intracorneal ring segments (ICRS):

ICRS consists of one or two semi-circle segments, operated into a surgically created tunnel in the mid corneal stroma. The ICRS are typically placed at the site of the steepest curvature and are designed to take up space in the stroma, thereby contributing to a decrease in curvature

Topography Supported Custom Ablation Photo-refractive keratotectomy (TOSCA PRK)

Used in contact lenses intolerant patients, TOSCA PRK has been successfully combined with collagen cross-linking (CXL) to treat both progression and refractive error

Collagen cross-linking (CXL):

Photochemical treatment of KC, consisting of loading of the corneal tissue with the photosensitizer riboflavin followed by irradiation with UVA-light. CXL has been shown to stiffen the cornea and halt the progression of KC.

Keratoplasty:

Generally accepted indications for keratoplasty in kerato-conus are poor visual acuity with contact lenses, contact lens intolerance or inability to fit/wear contact lenses, and nonresolving corneal hydrops.
  • Deep anterior lamellar keratoplasty (DALK)
  • Penetrating keratoplasty (PK)

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