Feasibility of constructing keratectasia animal model using collagenase type Ⅱ / 中华实验眼科杂志

Background Keratoconus is a chronic and progressive non-inflammatory ectatic disorder characterized by corneal thinning and irregular corneal topography,and its pathgenesis is a hot topic.A suitable animal model of keratoconus is still lacking,which limits the progress of relevant research.Corneal ectasia is a main anatomical basis of keratoconus,so we assume that keratoconus model could be constructed by simulating corneal ectasia.Objective This study was to investigate the influence of collagenase type Ⅱ on biomechanical responses detected by corneal visualization Scheimpflug technology (Corvis ST) and the feasibility of construction of rabbit model of corneal ectasia using coliagenase type Ⅱ.Methods This study protocol was approved by Ethic Committee of Peking University First Hospital and followed the Statement about experimental animal use and care from Association for Research in Vision and Ophthalmology (ARVO).Keratectasia models were established in 10 right eyes of 10 New Zealand white rabbits by soaking 8 mm-diameter central cornea using collagenase type Ⅱ solution prepared by PBS solution containing 15％ dextran (200 μl of 5 mg/ml) for 30 minutes after epithelial debridement,and only 200 μl PBS solution containing 15％ dextran was used in the same way in the left eyes as controls.The average corneal curvature (Km) and central corneal thickness (CCT) were measured with hand-held electronic corneal curvature meter and corneal ultra-sonic pachymetry respectively before modeling and 14 days after modeling.Corneal biomechanical parameters and intraocular pressure were measured in vivo by using Corvis ST at day 14 after modeling.The rabbits were sacrificed at day 14 after modeling,and corneal sections were prepared for hematoxylineosin staining and transmission electron microscopic examination.Results There were no significant differences in Km and C CT between model group and control group before modeling (Km:[48.28±2.29] D vs.[48.82± 1.63] D;CCT:[356.50± 19.13] μm vs.[356.20±21.66] μm;both at P＞0.05).The Km increased to (48.87±2.27) D and CCT decreased to (340.40±19.84)μm at day 14 after modeling,which were significantly different from (46.86±1.47) D and (367.80±23.38)μm (both at P＜0.01).The maximal deformation amplitude of model group and control group was (1.25±0.07) mm and (1.15 ±0.13) mm,respectively,showing a considerable difference between them (t=2.65,P＜0.05).No significant differences were found in applanation 1/2 time,applanation 1/2 length,applanation velocity,radius of curvature and peak distance between the two groups (all at P＞0.05).The morphology and ultrastructure examinations revealed that the arrangement of collagen fibers was loose and disorder and the interfiber space was enlarged in comparison with control group.Conclusions Collagenase type Ⅱ can lower corneal biomechanical properties.Soaking of cornea with collagenase type Ⅱ may be a potential way to establish a keratectasia animal model.

Clinical Results of Intacs(R) Ring Implantation in Keratoconus or Keratectasia

PURPOSE: To report the clinical results after the implantation of intrastromal corneal ring segments (Intacs(R)) 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.

Change of cornea posterior elevation after laser in situ keratomileusis / 中华实验眼科杂志

Background Keratectasia after laser in situ keratomileusis (LASIK) is one of the serious complications which affect the vision.The measurement of cornea posterior elevation is an important way helping to find this change.Objective The aim of this study was to investigate the change of cornea posterior elevation after LASIK in myopic eyes with astigmatism and affecting factors.Methods A series case-observational study was adopted.One hundred and twenty-seven myopic eyes with astigmatism of 66 patients who received LASIK in 2008 May through 2010 January in Beijing Tongren Hospital were retrospectively analyzed to evaluate the change of cornea posterior elevation following the LASIK.The parameters related to cornea posterior elevation were measured and compared before and 3 months,6 months and 1 year after surgery,respectively,with Oculyzer anterial segment analysis system.Results The height values from posterior cornea highest point,the lowest point and central vertex central elevation zone were (12.20±3.39),(-19.02±7.38) and (1.05 ±3.25) μm respectively before LASIK and were (14.38±3.80),(-18.55±7.11),(2.83±4.81)μm in3 months and (13.99±3.38),(-17.57±6.54),(2.45±4.61) μm in 6 months after LASIK.They were (14.40±3.85),(-17.76±6.00),(2.16±5.00) μm in 1 year after surgery.Significant increases were found in the vertex height and central elevation after LASIK compared with before surgery(highest pointq=6.813,5.594,6.875,all at P＜0.001.central vertex:q=4.488,P=0.002;q =3.530,P=0.013 ;q =2.799,P =0.047).However,no significant difference was seen in various time points after LASIK (P＞0.05).A positive correlation was obtained between the height value of the posterior cornea central vertex with the spherical equivalent (SE),maximum cutting depth or cutting proportion 1 year after LASIK (r =0.295,0.297,0.295,all at P=0.001),and there was a negative correlation between it with residual stroma (r=-0.208,P=0.019).The intraocular pressure (IOP) measured with noncontact tonometry (NCT) was (14.24±3.33) mmHg before LASIK,and those of 3 months,6 months and 1 year were (8.42± 1.90),(8.61 ± 1.64) and (8.76± 1.64)mmHg after LASIK,showing a significant lowing in IOP after LASIK in comparison with before LASIK (q =29.851,28.317,26.337,all at P＜0.001).But no significant change was found in the different time points after LASIK (P＞0.05).There was significant difference in the IOP corrected by Ehlers after LASIK (P＞0.05).The IOP before LASIK had positive correlation with the central elevation of posterior cornea surface 1 year after LASIK(r=0.258,P =0.003).Conclusions The cornea posterior elevation increases slightly early stage after LASIK but retains stable level with lapse of time.The refraction diopter before LASIK is the main factor affecting the posterior corneal shape.To reduce the risk of corneal ectasia,more attention should be paid to the reserving of appropriate corneal residual stroma and smallest degree of eccentricity during the ablation procedure.

Changes in Corneal Keratometry Readings after Corneal Collagen Cross-Linking Using Alcohol in Keratoconus Patients

PURPOSE: To evaluate the changes in corneal keratometry (K) readings after corneal collagen cross- linking (CXL) using 20% alcohol in primary keratoconus and keratectasia after refractive surgery. METHODS: Twelve eyes of 10 patients with primary keratoconus and 3 eyes of 3 patients with keratectasia after refractive surgery were included in the present study. Best-corrected visual acuity (BCVA) and mean K, corneal astigmatism by corneal topography, and mean K, corneal astigmatism, and spherical equivalent (SE) by auto refractometer were evaluated at baseline, and 6 months postoperatively. Eight eyes of 7 patients were also evaluated 1 year postoperatively. RESULTS: Mean BCVA improved from log MAR 0.66 +/- 0.50 to log MAR 0.55 +/- 0.58 (p = 0.100) at 6 month after CXL. In corneal topography, mean K significantly decreased from 50.04 +/- 5.88 D to 49.18 +/- 6.15 D (p = 0.019), and corneal astigmatism slightly decreased from 5.33 +/- 4.47 D to 5.29 +/- 4.88 D (p = 0.755) at 6 months after CXL. According to the auto refractometer, mean K significantly decreased from 48.53 +/- 5.94 D to 47.95 +/- 5.79 D (p = 0.038), corneal astigmatism significantly decreased from 3.95 +/- 2.54 D to 3.52 +/- 2.40 D (p = 0.010), and SE significantly decreased from -6.25 +/- 3.45 D to -5.40 +/- 2.91 D (p = 0.037) at 6 months after CXL. Significant mean K and corneal astigmatism decreases in topography were also observed at 1 year after CXL. Complications related to CXL were not observed. CONCLUSIONS: CXL using 20% alcohol appears to be a safe and promising treatment modality with less corneal stromal damage in progressive primary keratoconus and keratectasia after refractive surgery.

The Clinical Results of Intrastromal Corneal Ring Segment Implantation Using a Femtosecond Laser in Keratectasia

PURPOSE: To evaluate the clinical results of intrastromal ring segment (Keraring(R)) implantation using a femtosecond laser in patients with keratectasia. METHODS: Twenty eyes of 19 keratectatic patients (15 eyes of keratoconus and five eyes of post-LASIK keratectasia) who completed at least three months of postoperative follow-up were included in this study. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), spherical equivalent, keratometric value, corneal astigmatism, corneal higher order aberrations (HOA) and specular microscopy were determined or performed before and after surgery. In addition, intraoperative and postoperative adverse complications were recorded. RESULTS: UCVA improved in 13 out of 20 eyes (65%), and BSCVA improved in 16 out of 20 eyes (80%). At the postoperative examination there was no statistically significant reduction in the spherical equivalent with that observed at the examination before implantation. Conversely, there were statistically significant reductions in topographic mean K value and Sim K astigmatism, corneal total and coma-like HOA (p<0.05). On specular microscopy, there was no statistically significant difference between preoperative and postoperative endothelial cell density. There was one case of partial Descemet membrane detachment and one case of microperforation as a complication during surgery, which recovered over time without any treatment. CONCLUSION: Keraring(R) implantation appears to be an effective and safe procedure for improving visual acuity and stabilizing corneal refractive power in keratectactic patients.

Clinical Manifestation for Iatrogenic Keratectasia after Laser in Situ Keratomileusis (LASIK)

PURPOSE: This study was devised to report the clinical manifestations of the eyes developing keratectasia after laser in situ keratomileusis (LASIK). METHODS: In this retrospective study, among the 204 patients (408 eyes) who had LASIK between January 1996 and December 2001, charts of eleven patients (14 eyes) who developed post-LASIK keratectasia were reviewed. The mean follow-up was 36.18 months (range 12 to 67 months). RESULTS: Pre-LASIK corneal topographies of the patients shows that asymmetric bow tie pattern was the most common topographical finding (42.86%). The postoperative remaining corneal bed thickness (221.625 micro meter) of bilaterally afftected group was significantly lower than that (240.75 micro meter) of the unilaterally affected group (p=.0208), and the preoperative mean keratometric value (44.40D) was significantly higher than that of unilaterally affected group (p=.0212). The change of spherical equivalent and cylinder diopter value after LASIK was most prominent between one and four months postoperatively. CONCLUSIONS: LASIK is a highly effective procedure for correcting myopia, but in order to prevent serious postoperative complications such as keratectasia, we should be aware of the incitng factors listed above.

A Case of Keratectasia 5 Years after Photorefractive Keratectomy

PURPOSE: The clinically evident keratectasia has not been reported after photorefractive keratectomy (PRK) on the eyes with normal preoperative corneal topography. Herein, we present a case of keratectasia developed 5 years after PRK. METHODS: A 20-year-old man underwent the PRK for correction of myopic astigmatism in 1993. Preoperative manifest refractions were -4.00 D-0.50 D x 90degrees in the right eye and -3.75 D-0.75 D x 85degrees in the left eye. Although pachymetry was not performed, preoperative examinations including corneal topography did not show any sign of early keratoconus or forme fruste keratoconus. The operations were uneventfully performed on two eyes at an interval of one month. RESULTS: Up to 9 months after PRK, the patient's uncorrected visual acuity had been maintained 1.2 in both eyes. When the patient returned 5 years after PRK, he complained of decreasing visual acuity (0.5)in his right eye. During the next 2 years, the vision of the right eye was deteriorated to 0.04, and could not be corrected with the spectacles. The corneal topography of the right eye revealed profound steepeningjust inferior to the corneal center, and he had become contact lens intolerant. The left eye remained stable. The central corneal thickness was 419.0 micrometerin the right eye and 476.3 micrometerin the left eye.

Clinical Outcome of LASIK with Different Flap Thickness

PURPOSE: Since a few cases of keratectasia after LASIK were reported, the importance of residual corneal thickness has been emphasized. This study was to analyze adverse effects which may occur in reducing corneal flap thickness to increase residual corneal thickness. METHODS: A total of 237 eyes of 149 patients who had been followed up for 6 months or more after LASIK were evaluated retrospectively. Intended corneal flap thickness was 130 micrometer in 116 eyes(group A), and 160 micrometer in 121 eyes(group B) using an Automated Corneal Shaper(Chiron, USA). Clinical outcomes were compared between two groups. RESULTS: Except for some cases with retinal complication after surgery, 3 eyes lost best-corrected visual acuity by 2 lines or more in group A and 1 eye in group B, which was not statistically significant.(p>0.05) Fourteen eyes lost 1 line or more best-corrected visual acuity by postoperative irregular astigmatism in group A and 10 eyes in group B, which showed no significant difference, either. The incidence of flap-related complications such as wrinkling and free cap did not differ significantly between two groups(p>0.05). CONCLUSIONS: To leave residual cornea of greater thickness using a 130 micrometer thick flap rather than 160 micrometer may be a useful method to avoid postoperative keratectasia, one of the most severe complications.