Ji Ah Kim; Dong Hyun Kim; Won Ryang Wee; Mee Kum Kim

doi:10.7469/JKOS.2015.56.04.499

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Kim, Kim, Wee, and Kim: Clinical Results of Intacs® Ring Implantation in Keratoconus or Keratectasia

Original Article

J Korean Ophthalmol Soc 2015;56(4):499-508.

Published online: 7 September 2015

DOI: https://doi.org/10.7469/JKOS.2015.56.04.499

Clinical Results of Intacs^® Ring Implantation in Keratoconus or Keratectasia

Ji Ah Kim, MD^1,², Dong Hyun Kim, MD^1,², Won Ryang Wee, MD, PhD^1,², Mee Kum Kim, MD, PhD^1,²

¹Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea

²Laboratory of Ocular Regenerative Medicine and Immunology, Seoul Artificial Eye Center, Seoul National University Hospital Clinical Research Institute, Seoul, Korea

￭ Address reprint requests to Mee Kum Kim, MD, PhD Department of Ophthalmology, Seoul National University Hospital, #101 Daehak-ro, Jongno-gu, Seoul 110-744, Korea Tel: 82-2-2072-2665, Fax: 82-2-741-3187 E-mail: Kmk9@snu.ac.kr

Received 23 August 201422 September 2014 Accepted 23 March 2015

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

초록

Purpose:

To report the clinical results after the implantation of intrastromal corneal ring segments (Intacs^®) for the correction of keratoconus or keratectasia.

Methods:

This retrospective study was comprised of 16 eyes treated by insertion of intrastromal corneal ring and 30 eyes treated by penetrating keratoplasty (PKP) who were diagnosed with keratoconus or keratectasia. Visual acuity, refractive outcome, keratometric values were evaluated before and at 3 months, 6 months, and 12 months postoperatively. In addition, the implanted ring segment depth was measured by anterior segment optical coherence tomography and the results were compared based on the depth of the ring.

Results:

Twelve months after treatment, best corrected visual acuity (BCVA) was log MAR 0.32 at the ring group and log MAR 0.20 at the PKP group. BCVA change was larger at the PKP group than the ring group. Postoperative keratometric value was smaller at the ring group than at the PKP group. 3 mm irregular astigmatism was larger at the ring group than at the PKP group. The shallowly implanted ring group had a larger effect than the deeply implanted ring group.

Conclusions:

Intrastromal corneal ring segment implantation appears to be effective in improving the visual acuity and refractive outcome, although it cannot substitute for PKP.

Keywords: Intacs ring, Keratectasia, Keratoconus, Penetrating keratoplasty

References

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Figure 1.

Corneal topography (A) and pachymetric map of anterior segment OCT (B) were used to design axis and stromal depth of the ring location. OCT = optical coherence tomography; S = superior; I = inferior; T = temporal; N = nasal.

Figure 2.

Anterior to the ring (A) and posterior to the ring (B) portion of corneal thickness was gathered using anterior segment optical coherence tomography. Deep group is defined if (A) is same or longer than doubled (B). Shallow group is defined if (A) is shorter than doubled (B).

Figure 3.

Changes in UCVA and BCVA after Intacs® implantation. The BCVA improved at postoperative 3 months. UCVA = uncorrected visual acuity; BCVA = best corrected visual acuity. ^* Wilcoxon signed rank test.

Figure 4.

Changes in spherical equivalent (SE) after intacs implantation. The SE was improved at postoperative 12 months. ^* Wilcoxon signed rank test.

Figure 5.

Manifest astigmatism before surgery reduced on average following surgery. Each data point represents the astigmatism component of a power vector for one eye, referenced to the spectacle plane. J₀ = a Jackson crossed cylinder of power axes at 90 degrees and 180 degrees; J₄₅ = a Jackson crossed cylinder of power axes at 45 degrees and 135 degrees. Power vector analysis (S = spherical diopters; C = cylindrical diopters; α = axis (degree); J₀ = (-C/2) cos(2α); J₄₅ = (-C/2) sin(2α).

Figure 6.

Changes in Kmax, Kmin and Kastig after intacs implantation. All the values improved at postoperative 3 months. Kmax = Kmaximum; Kmin = Kminimun; Kastig = Kastigmatism. ^* Wilcoxon signed rank test.

Figure 7.

Changes in the irregular astigmatism of 3-mm and 5-mm area improved at postoperative 3 months. IR = irregular astigmatism. ^* Wilcoxon signed rank test.

Figure 8.

Complications of intrastromal corneal ring insertion. Marginal precipitation of the ring (white arrow head) is observed (A). Overlying stromal thinning (white arrow head) developed after new vessel formation (black arrow head) (B and C).

Table 1.

Demographics of the patients

	Intacs®	PKP	p-value^*
Total (n)	16	30
Mean age of Dx	22.20 ± 11.89	20.96 ± 10.18	0.726
Mean age of Tx	27.69 ± 11.77	27.10 ± 14.02	0.887
Sex (M:F)	8:8	17:13	0.674
Mean follow up (months)	17.44 ± 9.38	57.47 ± 34.96	0.000
BCVA (log MAR)	0.55 ± 0.46	1.71 ± 0.71	0.000
UCVA (log MAR)	1.26 ± 0.47	1.88 ± 0.61	0.001
SimK Max (diopter)	54.71 ± 6.98	56.34 ± 6.32	0.521
SimK Min (diopter)	48.91 ± 6.10	47.70 ± 8.06	0.648
SimK average (diopter)	51.81 ± 6.41	52.02 ± 7.02	0.935
SimK astigmatism (diopter)	5.80 ± 2.75	8.64 ± 3.54	0.022
K 3 mm IR (diopter)	7.10 ± 2.78	11.23 ± 3.64	0.003
K 5 mm IR (diopter)	7.58 ± 2.85	14.65 ± 3.77	0.000
Dsph (diopter)	-10.50 ± 1.22	-8.80 ± 5.34	0.261
Dcyl (diopter)	-4.25 ± 2.47	-5.33 ± 1.62	0.296
Spherical equivalent	-12.63 ± 1.85	-11.46 ± 5.03	0.660
Corneal opacity	0/16	22/30

Values are presented as mean ± SD unless otherwise indicated; Keratometry analysis excluded 17 eyes in PKP group who failed preoperative topography due to too steep cone; Refraction excluded 29 eyes in PKP group who failed preoperative refraction due to too severe irregular scissoring.

PKP = penetrating keratoplasty; Dx = diagnosis; Tx = treatment; BCVA = best corrected visual acuity; UCVA = uncorrected visual acuity; SimK = simulated keratometry; K = keratometry; IR = irregular astigmatism.

^* Independent student t-test.

Table 2.

Statistical summary of the distribution of manifest refractive errors before and after Intacs ring insertion

	M	J₀	J₄₅	B
Before surgery	-11.46 ± 5.03	0.30 ± 2.53	-0.07 ± 1.32	11.87 ± 4.84
After surgery	-6.90 ± 6.10	-0.17 ± 1.39	0.52 ± 2.11	7.54 ± 5.83
p-value^*	0.013	0.278	0.408	0.013

Values are presented as mean ± SD unless otherwise indicated; Power vector analysis ( S = spherical diopters; C = cylindrical diopters; α = axis (degree), Power vector = (M, J₀, J₄₅)), M = S + C/2; J₀ = (-C/2)cos(2α); J₄₅ = (-C/2)sin(2α); B = √( M²+ J²0+ J²45).

M = spherical lens of power; J₀ = a Jackson crossed cylinder of power axes at 90 degrees and 180 degrees; J₄₅ = a Jackson crossed cylinder of power axes at 45 degrees and 135 degrees; B = the pythagorean length of the power vector, measure of overall blurring strength of a spherocylindrical lens or refractive error.

^* Wilcoxon signed rank test.

Table 3.

Effect of insertion depth on the outcome

	Deep^* (n = 6)	Shallow^† (n = 9)	p-value^‡
Mean F/U (months)	12.0	18.63	0.187
BCVA (log MAR)	0.39	0.31	0.527
∆ BCVA (log MAR)	-0.05	-0.33	0.255
∆ Kmax	-4.52	-9.57	0.008
∆ Kmin	-4.03	-7.41	0.056
∆ K average	-4.28	-8.49	0.020
∆ Kastigmatism	-0.48	-2.16	0.139
∆ IR 3 mm	0.62	-0.78	0.061
∆ IR 5 mm	1.58	-0.49	0.069

Anterior to ring (A) and posterior to ring (B) portion of corneal thickness was gathered using anterior segment optical coherence tomography (OCT).

f/u = follow-up; BCVA = best corrected visual acuity; Δ = delta, changed value; K = keratometry; Kmax = maximum K; Kmin = minimum K; IR = irregualar astigmatism.

^* Defined if A is same or longer than doubled B;

^† Defined if A is shorter than doubled B;

^‡ Wilcoxon signed rank test.

Table 4.

Results of Intacs® insertion and PKP

	Intacs®	PKP	p-value^*
Mean f/u (month)	10.88 ± 6.11	20.43 ± 25.01	0.000
BCVA (log MAR)	0.32 ± 0.25	0.20 ± 0.16	0.153
Dsph (diopter)	-4.80 ± 5.82	-3.35 ± 4.19	0.350
Dcyl (diopter)	-4.41 ± 2.53	-3.37 ± 1.93	0.138
Spherical equivalent	-7.00 ± 6.06	-5.04 ± 4.00	0.201
Kmax	47.29 ± 4.47	50.06 ± 3.88	0.037
Kmin	43.10 ± 4.06	45.98 ± 4.18	0.032
K average	45.20 ± 4.17	48.02 ± 3.91	0.030
K astigmatism	4.19 ± 1.86	4.08 ± 1.95	0.849
IR 3 mm	6.93 ± 2.46	4.84 ± 2.01	0.004
IR 5 mm	7.91 ± 2.27	8.21 ± 2.50	0.694

Values are presented as mean ± SD.

PKP = penetrating keratoplasty; f/u = follow-up; BCVA = best corrected visual acuity; Kmax = maximum K; Kmin = minimum K; K = keratometry; IR = irregular astigmatism.

^* Independent student t-test.

Table 5.

Difference between before and after of Intacs® insertion and PKP

	Intacs®	PKP	p-value^*
∆ BCVA (log MAR)	-0.23 ± 0.50	-1.51 ± 0.69	0.000
∆ Dsph (diopter)	4.06 ± 5.34	6.00 ± 4.46	0.513
∆ Dcyl (diopter)	1.00 ± 2.72	0.00 ± 3.35	0.536
∆ Spherical equivalent	4.56 ± 5.73	6.00 ± 2.88	0.637
∆ Kmax	-7.42 ± 3.78	-6.45 ± 7.46	0.654
∆ Kmin	-5.81 ± 3.15	-2.22 ± 9.02	0.192
∆ K average	-6.62 ± 3.32	-4.34 ± 8.09	0.356
∆ K astigmatism	-1.61 ± 2.07	-4.23 ± 3.53	0.019
∆ IR 3 mm	-0.18 ± 1.45	-5.92 ± 3.44	0.000
∆ IR 5 mm	0.34 ± 2.22	-6.13 ± 4.13	0.000

Values are presented as mean ± SD.

PKP = penetrating keratoplasty; Δ = delta, changed value; BCVA = best corrected visual acuity; Kmax = maximum K; Kmin = minimum K; K = keratometry; IR = irregualar astigmatism.

^* Independent student t-test.

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