Surgical implantation of intrastromal corneal ring segments is one of the treatment options for contact lens-intolerant people living with keratoconus. This surgery is performed to lessen astigmatism and nearsightedness by reducing the cornea’s protrusion, which is the key clinical feature of keratoconus (per an article in Scientific Reports in 2019). The usual dome-shape of the cornea is cone-shaped in keratoconus, and this causes the refraction of light to be abnormal. As keratoconus progresses, the cornea’s “bulging” shape can become even more abnormal, and leading to more pronounced corneal thinning and worsening symptoms.
While corneal transplantation may be necessary in some people with keratoconus, corneal ring implantation has improved vision in many people with keratoconus who cannot wear either eyeglasses or contact lenses to correct vision. The Precision Keratoconus Center can assist you in understanding whether the placement of intrastromal corneal ring segments is likely to improve your vision.
Corneal Thinning and Protrusion – The Relationship Between Them
Thinning of the corneal stroma (a layer of the cornea) occurs in keratoconus, and this causes the protrusion of the cornea into its characteristic appearance upon clinical exam. As the thinning progresses over time, worsened eyesight is the main consequence. While the progression typically halts in the third or fourth decade of life, legal blindness can occur before keratoconus progression ceases. Meanwhile, the following symptoms may also occur:
- Blurred vision with a perception of “halos” in visual field;
- Sensitivity to light and glare;
- Corneal pain;
- Experience of “dry eyes” requiring a source of wetness (e.g., tears) for relief
Identifying the Layers of the Cornea
Besides its outer stratified layer, the cornea is composed of six distinct layers as described below (per an article in BioMed Research International in 2017):
- Squamous nonkeratinized epithelium;
- Acellular Bowman’s layer;
- Inner connective tissue stroma (with its resident keratinocytes);
- Pre-Descemet’s Dua layer;
- Descemet’s membrane;
- Cuboidal monolayered epithelium
In keratoconus-afflicted people, this article also reports that the collagen lamellae in the cornea’s stroma (layer accounting for 80 percent of the cornea’s thickness) are positioned at a wider angle than normal relative to the Bowman’s membrane. Consequently, this causes loss of the stroma’s interior lamellae which is linked to progressively corneal thinning. The foremost result is worsened visual acuity.
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Types of Intrastromal Corneal Ring Segments
According to an article in the Journal of Ophthalmology, the three most common brands of intrastromal corneal ring segments implanted worldwide are:
- Intacs (Addition Technology, Inc. in USA);
- Ferrara (Ferrara Ophthalmics, Ltd. in Brazil);
- Keraring (Mediphacos, Ltd. in Brazil)
However, a description on the American Academy of Ophthalmology’s website lists a total of four brands as follows:
- Intacs – arc length: 150; cross-section: hexagonal.
- Ferrara rings – arc length: 160; cross-section: triangular.
The National Keratoconus Foundation notes that Intacs received a Humanitarian Device Exemption (HDE) by the US Food and Drug Administration (FDA) in 2004 specifically for the management of keratoconus.
What to Expect in Corneal Ring Implantation Surgery
An article in Clinical Ophthalmology in 2018 reported that surgical channel creation for the placement of corneal ring segments into the periphery of the cornea can be achieved either by manual dissection or by using femtosecond (FS) laser. The corneal ring segments are then inserted into the created channels. Topical anesthesia is typically utilized for this “day-surgery” procedure, and antibiotics are normally prescribed for a week or more following surgery.
Corneal cross-linking (CSL) may also be performed in conjunction with corneal ring segment implantation, so understanding the surgical plan of action prior to arriving for the actual surgery is crucial to understanding the recovery period. Infection is the greatest risk in undergoing corneal ring segment implantation, as in any invasive eye procedure.
Scheduling an appointment at the Precision Keratoconus Center is a good way to enable you to acquire more knowledge of the surgical and nonsurgical treatment options available to people living with keratoconus.