Keratoconus – EyeWiki

Keratoconus

Prominent Keratoconus Cone
outstanding Keratoconus Cone
DiseasesDB
7158
ICD-10
H18.6
ICD-9
371.60
MedlinePlus
001013
MeSH
D007640

Keratoconus is an rare corneal disorderliness where the central or paracentral cornea undergoes progressive thin and steepening causing atypical astigmatism .

Disease Entity

Keratoconus adult center ( ICD-9 # 371.60 ) .

disease

Keratoconus is an rare corneal disorderliness where the cardinal or paracentral cornea undergoes progressive thin and steepening causing irregular astigmatism .

etiology

Etiology is unknown. however, it is associated with immediate allergy, Down ’ mho Syndrome, Leber ’ s congenital amaurosis, and Ehler ’ s Danlos/connective disorders. The familial design is neither outstanding nor predictable, but positive class histories have been reported. The prevalence of keratoconus if much reported to be 1 in 700. [ 1 ]

risk Factors

  • Eye rubbing, associated with atopy or vernal keratoconjunctivitis
  • Sleep apnea
  • Connective tissue disorders
  • Floppy eyelid syndrome[2]
  • Retinitis pigmentosa
  • Positive family history
  • Down syndrome

General Pathology

Keratoconus can show the pursue diseased findings ; fragmentation of Bowman ’ randomness layer, thinning of stroma and overlying epithelium, folds or breaks in Descemet ’ s membrane, and variable amounts of diffuse corneal scar. The american english Academy of Ophthalmology ‘s Pathology Atlas contains a virtual microscopy image of Keratoconus .

Pathophysiology

Histopathology studies demonstrated breaks in or complete absence of Bowman ’ second layer, collagen disorganization, scar, and thinning. The etiology of these changes is obscure, though some suspect changes in enzymes that lead to the breakdown of collagen in the cornea. While a genetic sensitivity to keratoconus is suggested, a specific gene has not been identified. Although keratoconus does not fulfill the criteria for inflammatory disease, holocene studies show a meaning function of proteolytic enzymes, cytokines, and rid radicals ( MMP-9, IL-6, TNF-α ) even in subclinical disease, showing a quasi-inflammatory characteristic in keratoconus. [ 3 ]

basal prevention

No hindrance strategy has been prove effective to date. Some feel that center rub or blackmail ( eg. sleeping with the hand against the eye ) can cause and/or lead to the progress of keratoconus. Patients should be informed not to rub their eyes. In some patients, avoidance of allergens and discussion of ocular come on disease may help decrease eye discomfort and consequently decrease eye friction .

diagnosis

diagnosis can be made by slit-lamp examen and observation of central or inferior corneal thinning. computerize videokeratography is useful in detecting early keratoconus and allows following its progression. Ultrasound pachymetry can besides be used to measure the thinnest zone on the cornea. New algorithms using computerize videokeratography have been devised which now allow the detection of forme fruste, subclinical, or suspected keratoconus. These devices may allow better screen of patients for prospective deflective operating room .

history

The majority of cases of keratoconus are bilateral, but much asymmetrical. The less affect eye may show a high measure of astigmatism or balmy steepen. Onset is typically in early adolescence and progresses into the mid-20 ’ randomness and 30 ’ sulfur. however, cases may begin much earlier or later in life, and progression may besides persist beyond the 30 ‘s. [ 4 ] There is a variable progress for each individual. There is much a history of patronize changes in eyeglasses prescription that do not adequately decline vision. Another coarse progress is from easy contact lenses to toric or astigmatism correcting contact lenses, to rigid gas permeable contact lenses. A accomplished ocular and medical history should be taken, including change in monocle prescription, decreased imagination, history of eye friction, medical problems, allergies, and sleep patterns .

physical examination

A thorough and accomplished eye examination should be performed on any affected role suspected of having keratoconus. The general health of the eye should be assessed, and appropriate accessory tests should be done to assess corneal curvature, astigmatism, and thickness. The best potential vision should besides be evaluated. many of the potential examination components are listed below :

  • Measurement of uncorrected visual acuity
  • Measurement of visual acuity with current correction (the power of the present correction recorded) at distance and when appropriate at near.
  • Measurement of best-corrected visual acuity with spectacles and hard or gas permeable contact lenses (with refraction when indicated)
  • Measurement of pinhole visual acuity
  • Retinoscopy to check for scissoring reflex
  • Slit-lamp biomicroscopy of the anterior segment including lid tightness and papillae in upper tarsal conjunctiva
  • Keratometry/Computerized Topography/Computerized Tomography/Ultrasound Pachymetry

Signs

early signs of Keratoconus include :

  • Asymmetric refractive error with high or progressive astigmatism
  • Keratometry showing high astigmatism and irregularity (the axis that does not add to 180 degrees)
  • Scissoring of the red reflex on retinoscopy
  • Inferior steepening, skewed axis, or elevated keratometry values on K reading and computerized corneal topography
  • Corneal thinning, especially in the inferior cornea. Maximum corneal thinning corresponds to the site of maximum steepening or prominence.
  • Rizutti’s sign or a conical reflection on the nasal cornea when a penlight is shone from the temporal side
  • Fleischer ring, an iron deposit often present within the epithelium around the base of the cone. It is brown in color and best visualized with a cobalt blue filter
  • Vogt’s striae, fine, roughly vertically parallel striations in the stroma. These generally disappear with firm pressure applied over the eyeball and re-appear when pressure is discontinued. Munson ‘s signboard

former signs of Keratoconus include :

  • Munson’s sign, a protrusion of the lower eyelid in downgaze.
  • Breaks in Bowman’s membrane
  • Acute hydrops, a condition where a break in Descemet’s membrane allows aqueous enter into the stoma causing severe corneal thickening, decreased vision, light sensitivity, tearing, and pain.
  • Stromal scarring after the resolution of acute hydrops, which paradoxically may improve vision in some cases by changing corneal curvature and reducing irregular astigmatism.

Symptoms

progressive changes in sight not easily corrected with eyeglasses .

clinical diagnosis

diagnosis is made based on the history of changing refraction, inadequate best spectacle-corrected sight, scissoring reflex on retinoscopy, abnormalities in keratometry, corneal topography, and corneal imaging, in association with corneal thin and deficient steepen ; characteristic slit-lamp findings can frequently be seen .

diagnostic procedures

diagnostic procedures include :

  • Slit-lamp examination
  • Retinoscopy (assessment of scissor reflex)
  • Hard or gas permeable contact lens trial as improved vision with lenses eliminates other sources of poor vision, including amblyopia
  • Measurement of K values
  • Ultrasound pachymetry
  • Computerized corneal topography

Example of Early Keratoconus as evidenced on a Placido-disc based topographic evaluation

  • Computerized corneal tomography (Rotating Scheimpflug, Rotating Slit Beam Photography)

Example of Keratoconus as evidenced on a Pentacam Scheimpflug evaluation Pentacam Image of Severe Keratoconus. Clockwise from top right, the 1st image displays elevated K readings and high astigmatism consistent with keratoconus, the anterior elevation map shows central protrusion, the posterior elevation map shows a corresponding area of central protrusion, and the pachymetric map displays central thinning. These are all diagnostic of ectasia.

differential diagnosis

  • Pellucid marginal degeneration
  • Keratoglobus
  • Contact lens-induced corneal warpage
  • Corneal ectasia post-refractive laser treatment

management

General discussion

The goals of treatment are to provide running ocular acuteness and to halt changes in the corneal supreme headquarters allied powers europe if progress. For ocular improvement and astigmatism management, spectacles or soft toric contact lenses can be used in mild cases. Rigid gas permeable contact lenses are needed in the majority of cases to neutralize the irregular corneal astigmatism. The majority of patients that can wear hard or gas-permeable contact lenses have a dramatic improvement in their vision. Specialty contact lenses have been developed to better fit the irregular and steep corneas found in keratoconus ; these include ( but not limited to ) RoseK, custom-designed contact lenses ( based on topography and/or wave front measurements ), semi-scleral contact lenses, piggyback lens use ( hard lens over easy lens ), scleral lenses, hybrid lenses, and PROSE ( prosthetic successor of the eyepiece surface ecosystem ). Those patients that become contact lens intolerant or do not have an satisfactory vision, typically from central scaring, can proceed to surgical alternatives. The primary discussion for progressive keratoconus, or keratoconus in youthful patients probably to progress at some point, is corneal collagen cross-link. A drug and device combination intersection ( Photrexa Viscous, Photrexa and the KXL System ) for epi-off corneal collagen cross-link was approved by the FDA in the spring of 2016. ceremonious corneal cross-link has been available under CE score throughout Europe for more than 10 years earlier throughout Europe. Corneal collagen cross-link is a minimally invasive treatment using vitamin b2 and UV light to induce stiffening of the corneal stroma through the geological formation of extra cross-link bonds within the extracellular matrix of the stromal collagen. In the ceremonious procedure, the corneal epithelium is debrided using standard clinical techniques, followed by soaking of the cornea with drops of ophthalmic vitamin b2 5-phosphate solution. The vitamin b2 sensitizer is then activated with exposure of the cornea to UV light for a time period of 30 minutes. Variations of this conventional “ epithelium-off ” proficiency involve higher intensities of UV for shorter time periods ( accelerated cross-link ) or non-removal of the epithelium ( “ epithelium-on ” ) techniques. The pivotal FDA trials and most european data sets demonstrate a high success rate for the conventional epithelium-off cross-link approach. other approaches have shown some promise and success but overall have been less reproducible and authentic in their abilities to halt keratoconus. [ 5 ] medical therapy for patients who have an episode of corneal hydrops involves acute management of the annoyance and well up. Patients are normally given a cycloplegic agent, sodium chloride ( Muro ) 5 % cream, and may be offered a imperativeness spot. After the imperativeness patch is removed patients may still need to continue sodium chloride drops or cream for respective weeks to months until the episode of edema has resolved. Patients are advised to avoid vigorous eye rub or injury. Patients are normally followed on a 3 to 6-month basis to monitor the progress of the corneal thin, steepening, the resultant ocular changes, and to re-evaluate the necessitate for cross-link and patient contact lens fit and concern. Patients with hydrops are seen more frequently until it resolves .

aesculapian therapy

Patients with consort medical conditions should have these attended to properly. Atopic or vernal conjunctivitis should be treated using topical anti-histamines, mast cell stabilizers, or anti-inflammatory/immunomodulatory treatments such as topical steroids, cyclosporine, tacrolimus, or lifitegrast. Since the incidence of sleep apnea is very high in keratoconus, and because this condition may contribute to the pathogenesis of keratoconus and other medical conditions, all keratoconus patients should be questioned regarding sleep habits. rest studies and CPAP masquerade break if found necessary are recommended for at-risk patients .

checkup follow up

Since the handiness of corneal collagen crosslinking, patients are normally followed on a 3 to 6-month footing to monitor the progress of the corneal cutting and steepen and the resultant ocular changes. This allows the doctor to determine if the cross-link treatment is indicated. cross-link is indicated at the attack of attested progress of keratoconus to improve the prognosis of the condition and preserve ocular function. These follow-up visits besides allow for re-evaluations of contact lens meet and concern .

surgery

The majority of patients with keratoconus can be fitted with liaison lenses, and their vision importantly improves with that. When patients become illiberal or no longer benefit from contact lenses, operation is the adjacent choice. If keratoconus is efficaciously stabilized with corneal cross-link while patients are distillery able to achieve adequate ocular affair with spectacles or liaison lenses, far interventions may not be required. surgical options include intrastromal corneal ring segments ( ICRS ), deep anterior lamellar keratoplasty ( DALK ), and penetrating keratoplasty ( PK ). Non-FDA approved treatments, which typically have less evidence-based information available on safety and efficacy, including the function of corneal cross-link experimentally combined with excimer laser discussion, conductive keratoplasty, [ 6 ] and/or ICRS. [ 7 ] Some surgeons will use phakic IOLs to address high myopia and some of astigmatism. ICRS have besides been approved for the treatment of mild to moderate keratoconus in patients who are contact lens intolerant. [ 7 ] In these cases, patients must have a clear central cornea and a corneal thickness of > 450 microns where the segments are inserted, approximately at 7 millimeter ocular zone. The advantage of ICRS is that they require no removal of corneal tissue, no intraocular incision, and leave the cardinal cornea untouched. Most patients will need spectacles and/or contact lenses post-operatively for best imagination but will have flat corneas and easier habit of lenses. If a affected role does not gain the have a bun in the oven results, ICRS can be removed, and then other surgical options can be considered. DALK involves the surrogate of the central anterior cornea, leaving the patient ’ second endothelium integral. [ 8 ] The advantages are that the risk of endothelial graft rejection is eliminated, and there is less risk of traumatic tear of the ball in the incision, since the endothelium and Descemet ’ randomness and some stroma are left integral, and faster ocular reclamation. There are respective techniques use including, manual dissection and big ripple technique to remove the anterior stroma while leaving Descemet ’ s level and endothelium uninfluenced. however, the procedures can be technically challenging requiring conversion to penetrating keratoplasty, and post-operatively there is the possibility of interface haze leading to a decrease in BCVA ; it is not clear if astigmatism is better treated with DALK vanadium PK. PK has a high achiever rate and is the standard surgical treatment with a long track record of safety and efficacy. Risks of this procedure include infection and cornea rejection and risk of traumatic rupture at the wound gross profit. many patients after PK may even need hard or gas-permeable contact lenses due to remainder atypical astigmatism. Any type of refractive procedure is considered a contraindication in keratoconic patients due to the capriciousness of the consequence and risk of leading to increased and mentally ill irregular astigmatism .

surgical follow up

Following any corneal surgical procedure, patients need to be followed to complete ocular rehabilitation. Most patients hush require imagination discipline with spectacles or contact lenses, and frequently hard or gasoline permeable lenses are required if high levels of astigmatism are introduce. All surgical patients need to be followed to ensure wound healing, evaluation for infection, suture removal, and early act center manage, such as testing for glaucoma, cataracts, and retinene disease. Graft rejection can occur after penetrating keratoplasty, requiring motivate diagnosis and treatment to ensure transplant survival .

Complications

contagion, inadequate wound healing, cornea transplant rejection, corneal neovascularization, graft-host junction reduce, glower, irregular astigmatism, and high refractive error .

prognosis

With early diagnosis and prompt treatment with corneal cross-link, patients may retain adequate ocular function with spectacle lenses or contact lenses throughout their life. ICRS can provide long-run success for patients with keratoconus, but this is typically in conjunction with liaison lens use, and some may ultimately require a corneal transplant to reach their goals of ocular rehabilitation. While the prognosis for penetrating keratoplasty in a keratoconic affected role is excellent, with most patients able to return to an active life style and the avocation of personal goals after ocular reclamation with specialization contact lenses, long term sustenance therapy with steroid medications may be required. “ Progression ” of keratoconus, even after corneal operating room, has been reported, but it is not clear how coarse or to what extent this can occur.

extra Resources

  • Boyd K, Huffman JM. Keratoconus. American Academy of Ophthalmology. EyeSmart® Eye health. https://www.aao.org/eye-health/diseases/keratoconus-list. Accessed November 17, 2022.
  • Boyd K, Huffman JM. Corneal Transplantation. American Academy of Ophthalmology. EyeSmart® Eye health. https://www.aao.org/eye-health/treatments/corneal-transplantation-list. Accessed November 17, 2022.
  • Boyd K, Mendoza O, Turbert D. Astigmatism. American Academy of Ophthalmology. EyeSmart® Eye health. https://www.aao.org/eye-health/diseases/astigmatism-4. Accessed November 17, 2022.
  • Cornea Atlas, 2nd Edition. Krachmer, Palay. Elsevier, 2006.
  • External Disease and Cornea, Section 8. Basic and Clinical Science Course, AAO, 2006.
  • Refractive Surgery, Section 13. Basic and Clinical Science Course, AAO, 2006.
  • Ocular Pathology Atlas. American Academy of Ophthalmology Web site. https://www.aao.org/resident-course/pathology-atlas.

References

  1. Hashemi H, Heydarian S, Hooshmand E, et aluminum. The prevalence and Risk Factors for Keratoconus : A Systematic Review and Meta-Analysis. Cornea. 2020 ; 39 ( 2 ) :263-270 .
  2. Ezra DG, Beaconsfield M, Sira M. et alabama. The Associations of Floppy Eyelid Syndrome : A Case Control Study. Ophthalmology. 2010 ; 117 : 831-838 .
  3. Lema I, Sobrino T, Durán JA, Brea D, Díez-Feijoo E. Br J Ophthalmol. 2009 Jun ; 93 ( 6 ) :820-4 .
  4. Gokul A, Patel DV, Watters GA, McGhee CNJ. The natural history of corneal topographical progress of keratoconus after age 30 years in non-contact lens wearers. Br J Ophthalmol. 2017 ; 101 ( 6 ) :839-844 .
  5. Lim L, Lim EWL. A Review of Corneal Collagen Cross-linking – current Trends in Practice Applications. Open Ophthalmol J. 2018 ; 12:181-213.
  6. Asbell, P.A. Is conductive Keratoplasty the Treatment of Choice for Presbyopia ? Expert Rev Ophthalmol. 2007 ; Feb:121-130 .
  7. 7.0 7.1 Asbell, P.A., Holmes-Higgin, D.K. : Intacs Corneal Rings Segments. In : Probst, L.E., Doane, J.F., Refractive Surgery : A tinge outline. Thieme, New York, 2001 .
  8. Bisbe L, Deveney T, Asbell PA. Big Bubble Keratoplasty, Expert Rev Ophthalmol. 2009 ; 4 ( 5 ) :553-561 .
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