CLINICAL

  ANTERIOR

MANAGING KERATOCONUS

WHAT TO DO WHEN YOUR PATIENT’S CORNEA IS WEARING THIN?

A 19-YEAR-OLD male presented complaining of blurred vision OU. He said he obtained prescription glasses a year ago elsewhere that “didn’t work well,” and he wanted an updated prescription. Exam revealed his BCVA with a manifest refraction failed to achieve 20/20 vision OU. The patient’s refraction produced 2.50D of cylinder OD and 3.25D OS with both meridians irregular. I suspected mild keratoconus.

Here, I discuss the etiology, symptoms, clinical signs, management options, as well as the ICD-9 codes associated with keratoconus and what happened with this patient.

ETIOLOGY

Keratoconus is a progressive, non-inflammatory corneal thinning dystrophy often diagnosed by O.D.s. Specifically, increased corneal curvature and structural change alters biomechanical properties, creating a weaker cornea that results in asymmetrical steepening and thinning. As the condition worsens, the cornea starts to protrude into a cone, resulting in increased steepness with progressive amounts of irregular astigmatism. Causative factors: genetics, mechanical eye rubbing, proteolytic enzyme digestion and the presence of the interleukin-1 beta promoter polymorphism.

Patients often present with keratoconus during the teen years (a mean age of 16), with progression typically lasting from 10 to 20 years. (Progression after age 40 is rare.) The condition is associated with posterior polymorphous corneal dystrophy, vernal keratoconjunctivitis, floppy eyelid syndrome, atopy, Down syndrome and various connective tissue diseases, such as Ehlers-Danlos syndrome and osteogenesis imperfecta.

Note the sufficient riboflavin absorbed in the cornea. This patient is ready for UV light therapy with CXL.

Also, keratoconus affects all races, with several studies estimating an incidence of 50 to 230 people per 100,000.

To diagnose the condition, a manual keratometer or a corneal topographer is needed to help detect steep corneas and irregular corneal astigmatism.

SYMPTOMS

• Bilateral blurred and distorted vision

• Glare

• Diplopia

• Photophobia

• Eyestrain

• Fatigue

• Corneal hydrops, causing excessive pain (severe case)

• Myopia (increases with severity)

• Astigmatism (increases with severity)

CLINICAL SIGNS

• Corneal ectasia

• Corneal steepening

• Fleischer rings (intraepithelial iron lines)

• Munson’s sign in down gaze

• Vogt’s striae

• Prominent corneal nerves

• Corneal scarring

MANAGEMENT OPTIONS

Three management options exist:

• Refraction. Prescribe glasses or soft contact lenses for early stages of keratoconus. Should either option fail, prescribe an RGP or hybrid specialty lens, which are designed to treat large refractive errors.

• Surgery. Refer patients for surgery when glasses and contact lenses fail to provide good vision, patients complain of discomfort with contact lens wear or when significant corneal scarring limits vision. These surgical options: implantable intracorneal ring segments (ICRS), Phakic IOLs and a full thickness PKP.

ICRS are small semicircular plastic rings of differing thickness and lengths designed to create central flattening to support the cornea via their 250µ to 300µ insertion into the midperiphery. They are used to treat small amounts of myopia and can be removed from the cornea if needed.

Phakic IOLs treat large amounts of myopia (-3.00D to -20.00D). Similar to cataract surgery, potential adverse events are very low. The choice between these procedures depends on surgeon preference.

Full thickness PKP is an excellent option for the management of full thickness corneal scars and severe keratoconus. The procedure replaces the central cornea (typically about 8.0mm of it) with a donor corneal tissue, providing a healthy, new clear visual axis. Recovery times can be long — in some cases a year or more — and there’s a 20% risk of graft rejection. Additionally, some patients develop secondary complications, such as glaucoma, increased IOPs and cataracts from the long-term steroid use. Further, PKPs often leave patients with large amounts of irregular astigmatism, which can range from as little as 0.25D of astigmatism to as much as 6.00D or more and can require an RGP contact lens to achieve good vision. Visual rehabilitation post PKP can also include PRK and toric IOLs to treat any residual refractive error.

• Collagen crosslinking. Although not yet FDA-approved, CXL uses riboflavin drops combined with ultraviolet light to reinforce the structural weakness in the stroma. It flattens the cornea, improves BCVA and UVA and prevents disease progression. In countries where this procedure is performed, 96% of treated eyes achieve stable topographies with no disease progression. Two versions of CXL are undergoing assessment in the United States: (1) epithelial removal referred to as “Epi-Off,” and (2): trans-epithelial “Epi-On,” which leaves the epithelium intact. Both methods can stop keratoconus progression, with young patients being the best candidates.

THAT PATIENT

I ordered a corneal topography and a manual pachymetry to evaluate the aforementioned patient’s cornea. Results showed inferior asymmetric corneal steepening that was OS with decreased corneal thickness inferiorly. As a result, I diagnosed him with forme fruste keratoconus; or subclinical keratoconus, and I educated him about his treatment options. He elected to continue wearing his current glasses and scheduled a follow-up visit in six months with one of our corneal specialists to consider CXL. Hopefully in six months this will be an FDA approved treatment option. OM

JOSH JOHNSTON, O.D., F.A.A.O., practices at Georgia Eye Partners. He focuses on ocular surface disease and has extensive experience in comanaging cataract and refractive surgery patients. Email him at drj@gaeye partners.com, or visit tinyurl.com/OMcomment to comment.