Medical Therapy
Medical therapy is limited to broad-spectrum topical antibiotics and corticosteroids for uncomplicated cases.
See Postoperative details and/or articles on ocular pharmacology for more information.
Surgical Therapy
See Intraoperative details for the surgical procedure.
Preoperative Details
The procedure for placement of the intrastromal ring and ring segments is similar, and both can be performed with topical anesthesia. The operative field is prepared, and the patient is prepared and draped in the usual sterile fashion for ophthalmic surgery. A lid speculum is used for globe exposure.
Intraoperative Details
Manual intrastromal corneal pocket creation
The corneal center is identified and marked with a Sinskey hook.
A 2-mm long epithelial impression is created at the 12-o'clock position, where the ring segments are to be placed at an 8-mm diameter optical zone.
A diamond blade, set at 65% of the peripheral corneal depth, is used to perform a radial incision along this mark. See the image below.
The 1.2-mm radial incision is made with a diamond knife at the edge of a 7-mm optical zone. The diamond knife is set for approximately two thirds of corneal depth. Reprinted with permission of Addition Technology Inc.
A vacuum-centering guide is positioned relative to the central corneal indentation.
The vacuum is increased, and the guide is circumferentially adhered onto the perilimbal conjunctiva, stabilizing the globe. This device provides a guide for the dissector. The dissector is inserted into the radial incision, and blunt dissection of the cornea at two-thirds depth is performed in the clockwise and counterclockwise directions to create 2 stromal channels. See the image below.
Rotation of the dissector creates the tunnel in the peripheral cornea into which an Intacs insert will be placed. Reprinted with permission of Addition Technology Inc.
The vacuum is released, and the vacuum-centering guide is removed.
Ring segments are inserted through the radial incisions using special forceps and are positioned using a Sinskey hook nasally and temporally, such that the superior ends are approximately 3 mm apart. See the images below.
The first Intacs insert is placed in the tunnel. Reprinted with permission of Addition Technology Inc.
The incision is closed with 1 or 2 interrupted 11-0 nylon sutures.
An Intacs insert in place at approximately two thirds of corneal depth. Reprinted with permission of Addition Technology Inc.
Postoperative Details
Postoperatively, antibiotic-corticosteroid combination drops and/or ointment are used, and the speculum is removed. The eye may be covered overnight with a shield. Antibiotic-corticosteroid combination drops are used 4 times daily for 1 week. The sutures are removed 2 weeks postoperatively or longer if the incision is not healed adequately.
Follow-up
Patients are seen postoperatively on day 1, week 1, and months 1, 3, 6, and 12. The surgeon should watch for postoperative complications. An observations timeline has been outlined for potential complications. See Complications.
Complications
Complications include localized incision-related epithelial defects, epithelial plug formation, wound dehiscence, superficial neovascularization, surgically induced astigmatism, infiltrates in the channel, transient decreased corneal sensation, and delayed infectious keratitis. [49, 50] Other observations included haze and deposits around the intrastromal channel.
Observations timeline consists of the following:
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Immediate (1-7 d)
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Early (1-4 wk)
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Intermediate (after 4 wk)
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Immediate postoperative observations may include epithelial defects, lamellar channel haze, undercorrection and overcorrection, and incision-healing responses.
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Early postoperative observations may include sterile infiltrates, epithelial cysts or plugs, and infectious keratitis.
Exchange or explantation
In selected patients with undercorrection or overcorrection, an exchange procedure can be done. In selected patients who are dissatisfied, an explantation procedure can be done. The procedures can be done with the patient using only topical anesthesia. The surgical steps are listed below:
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Early in the postoperative period, a Sinskey hook can be used to reopen the original incision, or, if the original incision is healed, a radial incision is made at the original site at the same depth as the original incision.
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Fibrous tissue is gently loosened with blunt dissection.
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A Suarez spreader is used to dissect the channel opening.
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A Sinskey hook is then used to engage the positioning hole and to rotate the segment out of its channel.
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In cases of exchange, a new ICR segment can then be placed into the previously made channel.
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The incision is closed with a suture.
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The same postoperative procedure is followed as with the original insertion.
Outcome and Prognosis
A summary of the safety and efficacy variables at 12 months after surgery is as follows:
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Uncorrected visual activity (UCVA) 20/20 or better (74%); UCVA 20/40 or better (97%)
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Mean refractive spherical equivalent (MRSE) ± 0.50 D (69%); MRSE ± 1.00 D (92%)
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Greater than or equal to 2 lines loss best spectacle corrected visual acuity (0%); increased cylinder greater than or equal to 2.00 D (0%)
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Corneal topography demonstrated that, while general flattening of the central cornea occurs, the normal positive asphericity of the cornea is maintained after placement of the ring and ring segments. [53]
Future and Controversies
Applications of intrastromal ring segments include the following:
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Myopia with astigmatism - Going beyond the range that has been approved by the FDA; currently, the upper limit is at -3.00 D spherical equivalent at the spectacle plane.
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Astigmatism - Applications in patients with pure astigmatism; currently, the upper limit is at +1.00 D of astigmatism.
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Presbyopia - In presbyopes and patients previously treated with LASIK or PRK
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Therapeutic indications - Intracorneal ring segments are now used in the management of ectatic corneal diseases. [63]
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Combination refractive procedures – Both the LASIK-Intacs method and the Intacs-LASIK method resulted in significant improvement in visual acuity and refraction based on limited experience. LASIK followed by Intacs may be the preferred procedure for reasons of safety, convenience, and lower induced cylinder.
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Enhancement - The correction of residual myopia following maximum corneal sculpting with LASIK or PRK (posterior stromal bed too thin for further ablation); improving the conditions of patients with decreased nighttime visual function (including halos, induced myopia, and decreased contrast sensitivity) following LASIK and PRK, associated with constricted optical zones. [64]
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Enhancement - Implantation of Intacs in eyes with myopic regression after LASIK and PRK resulted in a good refractive outcome and an improvement in uncorrected visual acuity. [65]
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KeraVision Intacs microthin prescription inserts. Reprinted with permission of Addition Technology Inc.
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KeraVision Intacs microthin prescription inserts. Intracorneal ring segments. Reprinted with permission of Addition Technology Inc.
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The 1.2-mm radial incision is made with a diamond knife at the edge of a 7-mm optical zone. The diamond knife is set for approximately two thirds of corneal depth. Reprinted with permission of Addition Technology Inc.
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Rotation of the dissector creates the tunnel in the peripheral cornea into which an Intacs insert will be placed. Reprinted with permission of Addition Technology Inc.
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The first Intacs insert is placed in the tunnel. Reprinted with permission of Addition Technology Inc.
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An Intacs insert in place at approximately two thirds of corneal depth. Reprinted with permission of Addition Technology Inc.
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Graphic representation of the intracorneal ring segments in place. Reprinted with permission of Addition Technology Inc.
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Intacs microthin prescription inserts treat mild myopia. Reprinted with permission of Addition Technology Inc.
Tables
Design |
Technique |
360° ICR |
Radial incision |
360° ICR |
Circumferential incision |
Gapped ICR |
Radial incision |
Intacs inserts |
Radial incision |
Intacs thickness (mm) |
Predicted nominal correction (D) |
Recommended prescribing range (D) |
0.25 |
-1.30 |
-1.00 to -1.625 |
0.30 |
-2.00 |
-1.75 to -2.25 |
0.35 |
-2.70 |
-2.375 to -3.00 |
