This course will review anterior segment pathologies and the role of anterior segment OCT in the fitting of scleral lenses to manage these conditions. Selected cases are included at the end of the course, as is a quiz.
The anterior segment includes structures in the front one-third of the eye, starting from the cornea to the crystalline lens. The cornea and ocular surface are especially complex, and, when functioning correctly, allow for clear and comfortable vision. However, significant visual impairment can result from abnormalities at the front of the eye, namely corneal ectasias and dry eye disease.
Anterior segment OCT can also be useful in managing glaucoma specifically when examining the angle, blebs, tubes and laser iridotomy assessments. Additionally it can help with managing ocular surface disorders such as dry eye disease, pterygia, pinguecula and scleromalacia. It can be helpful for surgical analysis for cornea, lens/cataract, biometry and LASIK. Anterior segment OCT provides a pivotal role in managing patients with corneal dystrophies and degenerations including keratoconus in addition to anterior segment tumors.
Keratoconus is a chronic, non-inflammatory ectasia of the cornea. It usually involves both eyes, but the severity per eye can be asymmetric. It is characterized by corneal steepening, visual distortion, corneal thinning, and central corneal scarring. Associated clinical findings that can be seen on slit lamp biomicroscopy are Fleischer ring, which are iron deposits around the cone’s base; Vogt’s striae, which are vertical stress marks in the areas of thinning; and apical scarring.
In Image 1, Fleischer ring is represented.
Image 1: Fleischer ring
In Image 2, we see an example of Vogt’s striae
Image 2: Vogt's striae
In Image 3, Apical Scarring is shown.
Image 3: apical scarring
Keratoconus can be diagnosed and managed with the aid of numerous testing.
The goal of keratoconus management is to improve visual function. In its earlier stages, vision can be corrected by spectacles and standard or custom soft contact lenses. With more progression, corneal rigid gas permeable lenses, hybrid lenses, or scleral lenses are utilized. Avoiding eye rubbing is another objective, as constant mechanical manipulation of the elastic cornea can morph the corneal curvature.1 Fortunately, there are many options for anti-allergy eye drops for symptomatic relief of itching.
The current available treatments for keratoconus aim to reduce progression, but cannot reverse pre-existing damage. Corneal cross-linking is the newest FDA-approved procedure to slow or halt progressive keratoconus. It utilizes riboflavin and ultraviolet light to reinforce the collagen within the cornea. INTACS, or intrastromal corneal ring segments, are another option, involving PMMA semicircular rings in the stroma to flatten the cornea. As a last avenue, corneal transplants are warranted when all other treatments have failed to preserve vision.
Dry eyes can sound like a mere nuisance, but keratoconjunctivitis sicca is the chronic dryness of the conjunctiva and cornea from an inadequate tear film. The etiology is often a combination of a tear production deficiency and inability to keep tears from evaporating from the eyes. This can change tear osmolarity and eventually lead to chronic ocular surface inflammation and corneal damage. Age, gender, medications, medical conditions, long-term contact lens use and history of LASIK can all contribute to dry eye disease. Symptoms can range from transient visual changes, discomfort, redness, photophobia, and pain. Various tests can assess dry eye disease, such as tear break up time, ocular staining, tear meniscus evaluation, Meibomian gland scans, and MMP-9 testing for tear film osmolarity.
Image 4: Significant ocular surface disease due to severe dry eye
Dry eye disease can be a primary problem, isolated to the ocular surface itself. However, significant, recalcitrant dry eye disease can be secondary to another underlying disease. This can include patients who have Stevens-Johnson syndrome, Sjogren’s syndrome, Graft versus Host Disease, ocular cicatricial pemphigoid, and limbal stem cell deficiency. Mechanisms that hinder complete lid closure and normal blinking can cause chronic exposure keratopathy, like in Graves’ disease and facial palsies.
Specific treatment regimens can be challenging to implement, given that each patient can have a unique clinical profile regarding severity and progression. The Tear Film & Ocular Surface Society (TFOS) has developed guidance in 2016 for a stepwise approach for managing dry eye disease.2
The Role of Scleral Lenses
Scleral lenses are not new, but have become more integrated into clinical practice since the 1980s and 1990s. They are currently used to manage corneal irregularities, such as keratoconus and complications post corneal transplants, as well as to protect the ocular surface especially in patients with keratoconjunctivitis sicca. Though the term “scleral lens” is commonly associated with large diameter scleral lenses, scleral lenses fall under the general umbrella of rigid gas permeable lenses and have different names based on the diameter of the lens.
Each lens brand has proprietary naming, but all essentially have three main zones. The optic zone vaults over the cornea with a fluid reservoir, simultaneously providing corneal hydration and optical correction. The transition zone overlies the limbus, and the haptic or landing zone rests on the conjunctiva.
Image 5 shows Scleral contact lens basic fit.