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Keywords:

  • astigmatism;
  • phakic intraocular lenses;
  • toric implantable collamer lens

Abstract

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. References

Background

The aim was to evaluate the safety, efficacy, stability and predictability of posterior chamber collagen copolymer phakic intraocular lens (pIOL) implantation to correct myopia and myopic astigmatism associated with keratoconus.

Methods

The unaided vision and visual acuity, refraction and adverse events were measured in 22 keratoconic eyes of 14 patients after using an implantable collamer lens (ICL) (STAAR Surgical Inc.) to correct refractive error. The outcome was evaluated over six months.

Results

The mean pre-operative spherical equivalent (SE) and cylinder changed from -4.98 ± 2.63 DS and -2.77 ± 0.99 DC to -0.33 ± 0.51 DS and -1.23 ± 0.65 DC, respectively at the end of six months. Before the surgery the mean Snellen decimal visual acuity was 0.63 ± 0.20. The mean unaided vision and visual acuity changed to 0.76 ± 0.23 and 0.85 ± 0.21, respectively at the end of six months. The mean safety and efficacy indices were 1.40 ± 0.32 and 1.24 ± 0.34, respectively. No eye lost a line of visual acuity and 17 eyes (77.3 per cent) gained one or more lines. Fifteen eyes (68.2 per cent) were within 0.50 D and 20 (90.9 per cent) were within 1.00 D of the desired spherical equivalent refraction. There was a change in manifest refraction of 0.09 ± 0.21 (ranging from -0.25 to +0.75) from one week to six months after the surgery.

Conclusion

The clinical outcomes of the current study demonstrate the safety, efficacy and predictability of toric implantable collamer lens in the correction of myopia and myopic astigmatism associated with keratoconus. The patients' refractions achieved early stability and remained stable during the course of the study.

Keratoconus is a serious progressive, non-inflammatory ectatic disorder associated with reduced corneal thickness and irregular astigmatism.[1] The treatment of keratoconus depends on the status of corneal ectasia and the resultant irregular astigmatism. Because of the biomechanical alterations of the corneal collagen compound, it has been suggested to use collagen cross-linking to halt the progression of keratoconus, when the progression has been confirmed.[2] Spectacles or soft contact lenses can be used in mild forms and when the corneal distortion and astigmatism increases, rigid gas-permeable contact lenses, intrastromal ring segments or keratoplasty might be used to improve the visual acuity.[2-4] The outcomes of other corrective methods like laser in situ keratomileusis (LASIK) seem to be unpredictable, as they may result in further thinning of the cornea and residual refractive error.[5, 6] Several studies[7-14] have used the phakic intraocular lenses (pIOLs) including posterior chamber pIOLs to correct refractive errors associated with keratoconus, suggesting a promising alternative. Currently, one of the most successful pIOLs, the Visian implantable collamer lens 4 (ICLV4) (STAAR Surgical Co., Monrovia, CA, USA) is under review by the United States Food and Drug Administration (FDA) for the correction of myopic astigmatism.[15, 16] The implantable collamer lens is a soft, foldable, single-piece plate and sulcus-placed posterior chamber phakic intraocular lens (IOL) made of collamer, which is a hydrophilic porcine collagen. The collamer is highly biocompatible and permeable to gas and metabolites and allows maintaining a normal crystalline lens metabolism, avoiding the development of cataracts. The implantable collamer lens is the only posterior pIOL that is currently approved by the FDA in the USA for the correction of moderate to severe myopia.[8, 14]

Meanwhile the potential side effects of this procedure remain to be investigated. This study aimed to assess the safety, efficacy, predictability and stability of the toric implantable collamer lens in patients with myopia and myopic astigmatism during a six-month period.

Methods

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. References

In this prospective study, the clinical outcomes of the implantable collamer lens to correct myopia and myopic astigmatism were investigated in 22 keratoconic eyes of 14 consecutive patients (Table 1). The patients were considered eligible to undergo implantation of the toric collamer lens if they were over 21 years of age, intolerant to contact lenses and spectacles, had a stable refraction for at least two years and were satisfied with their vision when wearing glasses. Patients had no other ocular and general pathology and no more than stage 3 keratoconus according to the Amsler-Krumeich classification.[18]

Table 1. Pre- and post-operative data six months after myopic phakic toric IOL implantation in 22 eyes of 14 patients with keratoconus
EyePatient/sex/age (years)S-Kr/F-KrPre-operative
IOPSphereCylinderAxisDVAACD
  1. DVA: distance visual acuity, UDV: uncorrected distance vision, WTW: white to white, STS: sulcus to sulcus, IOP: intraocular pressure, S-Kr: steep keratometry readings, F-Kr: flat keratometry readings, ACD: anterior chamber depth

 11/M/3346.00/49.0010-6.00-3.00106/7.53.40
 21/M/3347.00/49.509-6.75-3.00206/7.53.40
 32/M/3247.00/50.5010-3.25-4.00406/7.53.20
 42/M/3245.00/49.5010-1.75-4.001456/7.53.20
 53/M/2544.00/48.25110.00-4.001006/7.53.40
 64/F/3648.25/52.2511-2.00-3.25306/153.30
 74/F/3646.75/48.2511-2.25-1.251106/93.30
 85/F/2750.00/52.2510-4.50-2.25806/153.30
 96/M/3141.00/41.7512-2.00-1.50906/63.60
106/M/3141.00/43.0012-3.00-2.001356/123.60
117/M/3746.75/47.7516-6.00-1.501756/122.80
128/M/3643.50/46.75120.00-3.50806/123.00
139/M/4247.50/50.257-3.50-2.00506/93.22
149/M/4248.75/54.257-4.50-2.001706/123.22
1510/M/2744.50/47.75100.00-4.00156/63.20
1610/M/2744.25/47.50100.00-4.001706/7.53.20
1711/F/2642.25/43.7511-5.00-1.75456/93.03
1811/F/2642.50/44.5013-4.50-2.501556/123.03
1912/F/4643.75/46.7510-9.00-4.00956/182.90
2012/F/4642.25/44.7510-9.00-3.501006/182.90
2113/F/3447.50/50.5010-2.50-1.75306/93.00
2214/F/2642.75/45.5013-3.50-2.251356/153.05
WTWSTSTICL power, cylinder (D)/diameter (mm)Post-operative
IOPSphereCylinderAxisUDVDVA
11.9012.42-13.00, +3.50*100/125100.50-1.001756/66/6
11.9012.30-14.50, +3.50*110/125100.50-1.50456/66/6
12.0012.50-10.50, +6.00*130/125100.00-1.251556/66/6
12.0012.69-9.00, +6.00*55/125100.00-0.50806/66/6
11.5011.72-6.00, +6.00*10/120100.25-1.001356/7.56/6
11.9012.42-9.00, +5.50*120/125101.25-1.75656/156/9
11.9012.42-6.00, +2.00*20/125121.00-1.751506/126/9
11.5011.91-9.50, +3.00*170/1208-0.25-1.751556/126/9
12.0012.59-5.50, +2.00*180/130120.00-1.00406/7.56/6
12.0012.65-7.50, +3.00*45/130120.50-0.75356/66/6
11.0011.51-11.00, +2.00*85/115100.75-0.751556/7.56/7.5
12.0012.42-5.50, +5.50*170/125100.25-0.751706/66/6
11.5012.26-8.50, +3.00*140/12070.00-1.001806/7.56/7.5
11.5011.99-10.50, +3.00*80/12070.00-3.001306/126/9
11.0011.01-6.00, +6.00*105/115120.25-0.501506/66/6
11.0011.08-6.00, +6.00*80/115111.00-1.501356/96/6
12.0012.15-9.50, +2.00*135/125120.00-1.251756/7.56/6
12.0012.38-9.50, +3.00*35/12511-0.50-1.001756/96/6
11.1011.82-17.50, +5.00*5/115100.25-2.00306/186/18
11.1011.78-16.00, +4.00*10/115100.00-2.00506/156/15
11.5011.72-7.00, +3.00*120/120100.50-1.00406/66/6
11.5012.07-8.50, +3.00*45/120120.000.001806/96/9

Inclusion criteria were a chamber depth of greater than 2.8 mm (endothelium to anterior surface of the crystalline lens), an angle width of greater than 30°, a pupil diameter of less than 6.5 mm and white to white value (W to W) of more than 11.0 mm. Other inclusion criteria for implantation of the toric pIOL were distance visual acuity (VA) of 6/15 or better using glasses and a clear central cornea.[19]

Patients who were younger than 21 years, had an endothelial cell density (ECD) less than 2,000 cell/mm[2], a history of cataract, glaucoma, retinal detachment, macular degeneration, retinopathy, neuro-ophthalmic diseases or ocular inflammation were excluded from this study.

The lens power calculation was performed by the manufacturer (STAAR Surgical Co.) using a modified vertex formula. The calculation is based on the following variables: manifest and cycloplegic refractions for a vertex distance of 12.0 mm, keratometry and anterior chamber depth measured by Orbscan IIZ (Bausch & Lomb, New York, NY, USA).

For the pIOL sizing, W to W measurement was determined using Orbscan IIZ. Lens power calculation for the toric collamer lens was performed using the refractive astigmatic decomposition method described by Sarver and Sanders.[20] This method calculates the appropriate ICL cylinder using the patient's manifest refractive cylinder. Toric collamer lens calculation and implantation software allows the calculation of the spherical cylindrical power and length and also generates the toric collamer lens implantation diagram.[20]

In this study, the current V4 ICL design was implanted. Under topical anaesthesia, dilating agents were administered. For the toric ICL implantation, the surgeon marked the zero horizontal axis during slitlamp examination while the patient was lying upright to prevent cyclotorsion. In a temporal approach, after injection of viscoelastic material, a small 3.2 mm clear corneal incision was made and the collamer lens was injected through this incision into the anterior chamber and allowed to slowly unfold.

After injection of the toric collamer lens into the anterior chamber and its unfolding, the proper motion was performed with gentle posterior pressure and slight rotation of ≤1 clock hour using a modified ICL manipulator. This manoeuvre was repeated for all four footplates, positioning them under the iris plane. If any adjustment of the toric collamer lens was necessary, it was accomplished with a gentle movement touching the collamer lens at the junction of the optic and haptic. Toric implantable collamer lenses are manufactured to minimise rotation and require the surgeon to rotate the lens no more than 22.5° (three quarters of a clock hour) from the horizontal meridian. All toric implantable collamer lenses have an implantation diagram to demonstrate the amount and direction of rotation from the horizontal axis.

Irrigation and aspiration of the viscoelastic material were performed. An intraocular miotic (acetylcholine) was used to decrease the pupil size. At the end of implantation, a surgical peripheral iridectomy (PI) was performed using a vitrectomy probe (Storz Protégé, Bausch & Lomb) with a 200 mmHg vacuum and 30 cuts per minute speed.

Alignment of the toric implantable collamer lens was evaluated by slitlamp examination at all visits post-operatively. Subjective refraction was recorded as sphere, cylinder and axis and then converted to the power vector co-ordinates and overall blurring strength was calculated using this equation: M = S + 1/2 C, J0 = (-1/2C) cos(2ά), J1 = (-1/2C) sin(2ά), B = (M2 + J02 + J452)1/2, where M is the spherical equivalent (SE), S is the sphere, C is the cylinder, ά is the axis, J0 is the Jackson cross-cylinder axes at zero and 90 degrees, J45 is the Jackson cross-cylinder at 45 and 135 degrees and B is the overall blurring strength (Table 2).

Table 2. Summary of distribution of manifest refractive errors before and after myopic phakic IOL implantation using the power vector method
 Before lens implantationAfter lens implantation
MJ0J45BMJ0J45B
  1. Note. Manifest refractions in conventional script notation (S [sphere], C [cylinder] × φ [axis]) were converted to power vectors coordinates and overall blurring strength by the following formulas: M = S + C/2; J0 = (-C/2) cos (2φ); J45 = (-C/2) sin (2φ); B = (M2 + J02 + J452)1/2.

Mean-4.9770.0610.0595.26-0.3290.2010.0010.790
SD2.6331.1550.9572.4920.5140.3340.5860.472

Results

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. References

There were no complications during the surgical procedures. No eye needed explantation. Two eyes needed repositioning due to the off-axis alignment (more than five degrees). There was no decentration of the collamer lens and no case of pupillary block was detected. There was no significant increase in intraocular pressure (IOP) at first week or second and sixth months after the operation. Mean IOP was 10.27 ± 1.49 at six months. No case of anterior subcapsular cataract developed and no patient reported halo, glare or starburst during daylight or under dim conditions.

We studied 22 eyes of 14 patients. The mean spherical equivalent pre-operatively was -4.98 ± 2.63 D (ranging from -1.75 to -11.00 D). The mean spherical equivalents after surgery at one week and two months were -0.42 and -0.38 D, respectively. At six months, the mean spherical equivalent was -0.33 ± 0.51 D. Fifteen eyes (68.2 per cent) were within 0.50 D and 20 eyes (90.9 per cent) were within 1.00 D of the desired spherical equivalent refraction (Figure 1).

figure

Figure 1. Post-operative spherical equivalent (SE) at two and six months

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The mean pre-operative refractive cylinder was -2.77 ± 0.99 DC (ranging from -1.50 to -4.00 DC). The mean refractive cylinders at one week and two months after surgery were -1.25 and -1.28 DC, respectively. Six months after surgery, the mean refractive cylinder was -1.23 ± 0.65 DC (ranging from zero to -3.00 D), while three eyes (13.6 per cent) had 0.50 D or less of refractive cylinder at six months (Figure 2). Seventeen eyes (77.27 per cent) and 15 eyes (68.18 per cent) were within 0.50 D for J0 (r2 = 0.99) and J45 (r2 = 0.90), respectively.

figure

Figure 2. Post-operative refractive cylinder at two and six months

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Twenty-one eyes (95.5 per cent) with collamer lenses had 2.00 D or less of refractive cylinder at six months, compared to five (22.72 per cent) pre-operatively and 12 eyes (54.5 per cent) had a refractive cylinder within 1.00 D. There was a change in manifest refraction of 0.09 ± 0.21 (ranging from -0.25 to +0.75) from the first week to the sixth month after surgery (Figure 3).

figure

Figure 3. Stability of spherical equivalent and refractive cylinder

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Before surgery the mean Snellen decimal VA was 0.63 ± 0.20. The mean unaided distance vision[19] was 0.76 ± 0.23 (range 0.3 to 1.0) and the mean VA was 0.85 ± 0.21 (range: 0.3 to 1.0) six months post-operatively. VA was 6/18 or better in 100 per cent of eyes and 6/9 or better in 20 eyes (90.9 per cent). The mean efficacy index (mean post-operative unaided vision divided by mean pre-operative VA) was 1.24 ± 0.34 when measured six months after the operation. There was no case of VA loss. Seventeen eyes (77.3 per cent) gained one or more lines. The mean safety index (mean post-operative VA divided by mean pre-operative VA) was 1.40 ± 0.32, when determined six months after surgery. Figures 4 and 5 show cumulative pre-operative unaided vision and VA two and six months post-operatively.

figure

Figure 4. Cumulative pre-operative unaided vision and five days, two and six months post-operative unaided vision

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figure

Figure 5. Cumulative pre-operative and two and six months post-operative VA

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There was an increase in the number of eyes with VA of 6/6 or better from 9.1 per cent (two eyes) at baseline to 59.1 per cent (13 eyes) after six months (Figure 6).

figure

Figure 6. Gain and loss of lines in VA. The figure shows no loss of VA.

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Eight eyes (36.4 per cent) had 6/6 or better unaided vision six months post-operatively, compared to two (9.1 per cent) with VA better then 6/6 at baseline. Furthermore, 19 eyes (86.4 per cent) had unaided vision equal to or better than the pre-operative VA six months following the operation. Figures 7, 8 and 9 show predictability of manifest refraction spherical equivalent (MRSE) and J0 and J45 for cylinder (attempted versus achieved) among patients.

figure

Figure 7. Scatter plot diagram of attempted and achieved of spherical equivalent

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figure

Figure 8. Scatter plot diagram of attempted and achieved J0

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figure

Figure 9. Scatter plot diagram of attempted and achieved J45

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Discussion

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. References

In this prospective study, the clinical outcomes of ICL implantation of collamer lenses to correct myopia and myopic astigmatism were investigated in 22 eyes of 14 consecutive patients with keratoconus. The safety, predictability, stability and efficacy of this method were also determined.

Posterior chamber phakic IOLs can be considered a safe technique to treat refractive errors in keratoconic patients with better cosmetic outcomes, because of position of the IOL behind the iris.[15, 16]

At present, toric implantable collamer lenses are available with spherical powers from -3.00 to -23.00 D for correction of myopia and a refractive astigmatic power up to 6.00 D. In relation to efficacy, unaided vision is the first parameter to measure in any study of refractive surgery. In this study, eight eyes (36.4 per cent) had 6/6 or better unaided vision at the end after six months, compared to two eyes (9.1 per cent) at baseline. Furthermore, after six months, 19 eyes (86.4 per cent) had unaided vision equal to or better than the pre-operative VA. The efficacy index at six months was 1.24 ± 0.34 and the safety index was 1.40 ± 0.32. There was a change in manifest refraction of 0.09 ± 0.21 from the first week to the sixth month after surgery.

Previous studies[18, 20-26] have demonstrated that toric collamer lens implantation is a safe and effective treatment, which provides stability and predictability in patients with myopic astigmatism. Kamiya and colleagues[23] reported that the logarithm of the minimum angle of resolution (logMAR) unaided vision and VA were -0.11 ± 0.12 and -0.19 ± 0.08, respectively one year after lens implantation for myopic astigmatism among their patients, providing safety and efficacy indices of 1.17 ± 0.21 and 1.00 ± 0.29, respectively. A change in manifest refraction of -0.07 ± 0.27 D happened from one week to one year after surgery. Ninety per cent and 100 per cent of the eyes were within 0.5 and 1.0 D of the targeted correction, respectively, 12 months after surgery.[23]Hashem, El Danasoury and Anwar[27] using toric implantable collamer lenses in patients with myopic astigmatism, showed that 96.8 per cent of eyes had eight degrees or less and 90.3 per cent had five degrees or less of axis misalignment.

Alfonso and colleagues[28] reported early predictability and stability after toric collamer lens implantation in keratoconic eyes. In their study, the safety and efficacy indices were 1.16 and 1.07, respectively. In another study, Kamiya and colleagues[29] reported safety and efficacy indices six months after toric lens implantation in keratoconic eyes of 1.12 ± 0.18 and 1.01 ± 0.25, respectively. Eighty-five and 96 per cent of the eyes were within 0.50 and 1.00 D, respectively of the targeted correction and there was a change of 0.00 ± 0.35 D in manifest refraction from the first week to the sixth month post-operatively. The only two realignments were performed at one week post-operatively and remained stable for six months.

There are studies on the usefulness of spherical anterior chamber IOL implantation to treat these patients. They show that, although the residual spherical value (about 1.00 D) and the safety are the same as other studies, the amount of residual refractive astigmatism is unchanged, especially in eyes with keratoconus.[30] Alfonso, Palacios and Móntes-Micó[14] reported favourable safety, efficacy, predictability and stability after non-toric collamer lens implantation for myopia among keratoconic patients. The safety and efficacy were reported to be 1.05 and 0.98, respectively and VA significantly improved after surgery; however, the amount of pre-operative manifest refractive astigmatism was low (1.24 ± 1.19 D) among their patients.

Leccisotti and Fields[31] first reported using phakic IOLs to correct myopia. They used angle-supported phakic IOLs and reported improved VA and unaided vision among patients. They also reported that using a corneo-scleral incision is not suitable for correcting refractive astigmatism in these patients.

Budo, Bartels and van Rij[32] reported implantation of artisan toric pIOLs in both eyes of three patients with keratoconus. Four out of the six eyes were within ± 1.00 D after six months. They reported a higher reduction in the spherical component (87.4 per cent) compared to the refractive astigmatism (64.5 per cent).[32] It seems that incision-induced astigmatism was related to poor predictability of refractive astigmatism correction.

The other options for treating keratoconus are intracorneal ring segments (ICRS) and collagen cross-linking (CXL). Although ICRS (Intacs™, Addition Technology Inc, Fremont, CA, USA) (Ferrara Rings™, Keraring™, Mediphacos, Belo Horizonte, Brazil) could improve visual outcomes through strengthening of the corneal structure and reshaping of the cornea, the refractive results are not predictable, especially in higher refractive errors. The same fact also pertains to collagen cross-linking. These procedures may be inefficient; however, there are reports[33-36] of intracorneal ring segment implantation combined with phakic IOL. Because of the high astigmatism in patients with keratoconus, it seems that the implantation of phakic IOLs after intracorneal ring segment implantation or collagen cross-linking in sequential procedures is more predictable.[37]

It should be mentioned that patients with advanced keratoconus (keratoconic patients with poor spectacle VA who may be dependent on rigid lenses) or those with a documented progressive disease will not fulfil the inclusion criteria for pIOLs and for those patients, collagen cross-linking or intracorneal ring segments may produce promising results. In more advanced forms, corneal transplantation remains the procedure of choice.

In conclusion, the present study demonstrated that the use of toric implantable collamer lenses in keratoconic patients with myopia and myopic astigmatism is a safe and effective procedure with acceptable predictability and excellent stability up to six months.

References

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. References
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