OCT in Corneal Leucoma as a Criterion for PKP

Optical coherence tomography (OCT), also called optical tissue biopsy, is a noncontact method of structure-deep tissue penetration. Introduced by James G. Fujimoto, PhD, of MIT, OCT has the ability to: (1) diagnose holes in the macula lutea, (2) estimate retinal fluid spaces and retinal membranes in the posterior segment, (3) check the position of deposits in the cornea, (4) visualize Descemet's membrane detachment, and (5) monitor patients with corneal diseases or those who have undergone corneal transplantation.

As a noncontact procedure, OCT has traditionally been used to diagnose problems in the posterior segment of the eye. More recently, it has also become useful to diagnose problems in the anterior segment. Anterior segment OCT is becoming more common, particularly in specialized surgeries such as keratoplasty, endothelial transplantation, phakic IOL implantation, and cataract and glaucoma surgery. Addtionally, anterior segment OCT is useful for imaging corneal structures.

SPECIFICATIONS OF ANTERIOR SEGMENT OCT
The Visante OCT (Carl Zeiss Meditec AG, Jena, Germany; Figure 1) uses a 1310-nm wavelength generated by a superluminescent diode. Pigment blocks the infrared light; however, the light passes through nonpigmented opaque structures, and images can be obtained through a cloudy or white cornea, conjunctiva, and sclera. The axial resolution (penetrating) is 18 µm, and the transverse resolution is 50 µm. The surgeon can choose the examination axis within 360? in four specific axes.

High-resolution OCT images can be used to evaluate the corneal structures, Descemet's membrane detachments, depth of alteration, deposits, scars and foreign bodies, descemetocele, and corneal dystrophy alterations. They enable measurement of the cornea and its layers (eg, anterior flap thickness after LASIK, anterior lamellar transplantation, lamellar posterior flap thickness after endothelial transplantation). The Visante OCT also enables the surgeon to visualize alterations in the anterior chamber even if the patient's cornea is opaque.

Not only does the Visante OCT allow visualization of the position of anterior and posterior chamber phakic IOLs, but it can also be used to discover the presence of vitreous, blood, effusion fluid, foreign bodies, and antiglaucoma implants or shunts. The device allows picture acquisition, even in a cloudy cornea, and enables the surgeon to visualize the state of the iris, including its anatomy, nodules, and cysts. The Visante OCT can also estimate the patency of iridotomy and iridectomy. The iridocorneal angle is clearly visible, therefore allowing measurement of its width and its dynamics of change. Screening for angle status and closed-angle glaucoma risk can be performed quickly with this device. Obtaining a pachymetry map across a 10-mm area of the cornea is especially valuable for the detection of keratoconus, conditions after refractive surgery (ie, presence of corneal ectasia or thickness of haze), and other corneal pathologies.

CASE PRESENTATION
Five years prior to presentation, a 76-year-old female with corneal degeneration underwent phototherapeutic keratectomy (PTK). Routine follow-up after the initial procedure revealed neither pain nor complications (Figures 2 and 3). The patient recently stumbled on a set of stairs, and 2 weeks afterward, she began experiencing significant pain.

During clinical examination, UCVA in her right eye was light perception and intraocular pressure (IOP) was 48 mm Hg. The IOP was not lowered sufficiently with pharmacologic intervention and a subsequent transscleral cyclophotocoagulation procedure (range, 34–45 mm Hg).

Ultrasound biomicroscopy showed no abnormalities, and only partial closing of the iridocorneal angle. The posterior segment ultrasonography was normal.

Based on the patient's (1) pain profile, (2) high IOP, and (3) poor visual acuity, standard practice dictated that we present her the option of enucleation to improve her condition. Before making the final determination to proceed with enucleaution, we examined her eye with the Visante OCT. The scans showed several abnormalities in the anterior chamber, a membrane linking the iris to the cornea, iris thickening, closure of the iris and cornea angle, a plane cluster of the iris with peripheral cornea at about 270?, and a membrane closing the iris (Figure 4A, 4B).

These findings suggested the presence of lens fragments in the anterior chamber and complete resistance to the outflow of the aqueous humour, which explained the high IOP and the accompanying pain. We decided to perform penetrating keratoplasty (PKP) as an alternative to enucleation.

SURGERY OF THE RIGHT EYE
Corneal graft preparation, lens fragment removal from the anterior and posterior chambers, synechiotomies, anterior vitrectomy, and corneal graft suturing were performed. We did not implant an artificial lens because of optic nerve atrophy and long-lasting poor visual acuity (Figure 5).

The treatment was successful. Postoperatively, IOP ranged from 15 to 18 mm Hg; however, UCVA and BCVA were still light perception. The patient did not experience any complications, and the pain subsided. No immunosupression was necessary. We monitored the patient for 2 years and found that corneal graft stabilization and proper adhesion occurred postoperatively (Figure 4C, 4D).

DISCUSSION
For this case, the Visante OCT provide a detailed analysis of the eye, facilitating our decision to perform PKP. Anterior-segment OCT imaging suggested the presence of lens structures in the anterior chamber and complete resistance to the outflow of the aqueous humor, which explained the inability to reduce IOP and the accompanying pain. After intervention with PKP and removal of the lens fragments, the pain ceased and IOP stabilized, which increased the patient's comfort. Unfortunately, the patient's visual acuity did not improve.

Similar to the recent evolution of posterior segment diagnostics, future improvements of the Visante OCT for anterior segment examination and diagnostics will include more precise images, higher resolution, and 3D reconstruction of the structures under examination. In my opinion, this system of imaging will almost certainly replace the invasive anterior segment ultrasound biomicroscopy. In the future, 3D anterior segment spatial reconstruction, as well as the ability to obtain images of nearly histologic quality, will be possible.

Ewa Mrukwa-Kominek, MD, PhD, practices in the Department of Ophthalmology, Silesian Medical University, Katowice, Poland. Dr. Mrukwa-Kominek states that she has no financial interest in the products or companies mentioned. She is a member of the CRST Europe Editorial Board. She may be reached at tel: +48 601528850; e-mail: emrowka@poczta.onet.pl.

Stanislawa Gierek-Ciaciura, MD, PhD, practices in the Department of Ophthalmology, Silesian Medical University, Katowice, Poland. Dr. Gierek-Ciaciura states that she has no financial interest in the products or companies mentioned. She may be reached at tel: +48 601898896; e-mail: ciaciura@kil-okul.katowice.pl.