2005 ESCRS Ridley Medal Lecture

Ten-year follow-up of corneal cross-linking and refractive surface ablation in patients with asymmetric corneal topography

Purpose

Compare the safety and efficacy of wavefront-guided photorefractive keratotomy (PRK) 6 months after cross-linking (CXL) to wavefront-guided PRK alone for refractive correction in patients with bilateral asymmetric corneal topography.

Methods

Prospective randomized clinical trial with 16 patients (32 eyes). CXL with subsequent PRK after 6 months in one eye, and PRK alone was performed in contralateral eyes. The follow-up was 10 years. We analyzed visual outcomes, Scheimpflug topography, and corneal haze evaluation.

Results

Eyes in the PRK group showed better results than in the CXL + PRK group. Mean postoperative CDVA was 0.044 logmar (SD, 0.073) in the PRK group and 0.1 logmar (SD, 0.21) in the CXL + PRK group, the mean sphere was + 0.21 (SD, 0.6) D in the PRK group and 0.87 (SD, 2.3) D in the CXL + PRK group, and mean SE was -0.35 (SD, 0.65) D in the PRK group and 0.62 (SD, 2.32) D in the CXL + PRK group. In one patient, a steepening of 2.5 D and a thinning of 17 μm occurred in PRK alone group. Two patients in the CXL + PRK group presented corneal haze. The overall complication rate was 18,75% (haze and ectasia).

Conclusion

Non-simultaneous CXL and PRK procedures yielded good refractive results, but worse than those obtained with PRK alone. Although one patient in the PRK group developed corneal ectasia, the CXL + PRK group had a higher loss of vision lines, indicating less safety.

Evaluation of Ocular Higher-Order Aberrations in First-Degree Relatives of Patients With Keratoconus

PURPOSE

The aim of this study was to evaluate the corneal higher-order aberrations (HOAs) in first-degree relatives of patients with keratoconus (KCN) and compare with the normal population.

METHODS

In this prospective comparative study, 210 eyes from 105 family members of 28 patients with KCN and 210 normal eyes of 105 controls were enrolled. In each eye, corneal topography, tomography, and aberrometry were performed and compared between the 2 groups.

RESULTS

This study included 61 female (58.1%) and 44 male participants (41.9%) and 105 age-matched and sex-matched controls with normal topographic cornea. In 14 of 105 first-degree relatives (13.33%) of patients with KCN, KCN was diagnosed with a male preponderance (71.5% male, 28.5% female). Tomographic indices and irregularity indices in 3 and 5 mm zone in Orbscan were significantly higher in the relative group. In addition, other irregularity indices of TMS-4 topography including surface regularity index, surface asymmetry index, difference sector index, SDP, and irregular astigmatism index were significantly higher in family members of patients with KCN. The most prevalent topographic pattern in the control group was the symmetric bowtie (57.1%) and in the relative group was the asymmetric bowtie (39.5%). In addition, significantly thinnest corneal pachymetry was detected in the relative group. Root mean square of all HOAs including vertical trefoil, vertical coma, horizontal coma, horizontal trefoil, quadrifoil, and fourth-order spherical aberrations were significantly greater in the relative group than controls.

CONCLUSIONS

Owing to the high prevalence of undiagnosed KCN susceptibility in family members with KCN, keratorefractive surgery should be considered cautiously in these individuals. In addition, comprehensive preoperative examination should be considered to detect subtle topographic and HOAs in these individuals.

Keratectasia after laser-assisted subepithelial keratectomy for myopia: A case report

RATIONALE

Recently, some ophthalmologists performed PRK or LASEK surgeries in FFKC suspicious patients, which is supposed to prevent FFKC evolvement via fibrotic scar formation. Our report indicates that keratectasia can occur after LASEK in FFKC suspicious patients, highlighting the importance of stricter regulation of patient recruitment before the procedure and postoperative follow-up.

PATIENT CONCERNS

This is a report of a 25-year-old man with poor corrected distance visual acuity (CDVA) 6 years after LASEK. Preoperatively, central corneal thickness was 532 μm in right eye and 528 μm in leftt eye; corneal keratometry was 42.0/40.3diopters (D) in the right eye and 42.5/40.6D in the left eye; the CDVA was 2/50 in both eyes with the CDVA being 20/20 with -6.00DS/-2.00DC×30 in the right eye and -8.00DS/-2.00DCx150 in the left eye. Six years after LASEK, the CDVA was 20/50 with -5.75DS/-1.75DC×170 in the right eye and 10/50 with -15.00DS/-5.00DC ×155 in the left eye.

DIAGNOSES

Bilateral keratectasia.

INTERVENTIONS

Slit lamp examination, postoperative and in vivo confocal microscopy (IVCM) were performed in both eyes.

OUTCOMES

Examination under the slit lamp showed thinning and protrusion of the central cornea. Corneal topography showed significant inferior steepening with an irregular astigmatism, the corneal thickness at the thinnest point was 376μm and 350 μm and anterior surface keratometry was 43.1/41.2 D and 50.0/48.4 D in the right eye and left eye, respectively (right eye maximum K, 52.1 D; left eye maximum K, 65.6 D). Thin and irregular bands and hyper-reflective deposits in the Bowman's layer were found in IVCM images.

LESSONS

The case indicates that ectasia can occur after LASEK in pre-existing forme fruste keratoconus (FFKC) suspicious patients, highlighting the importance of a stringent preoperative workup on patients before the procedure and proper postoperative follow-up.

Evaluation of the toric implantable collamer lens for simultaneous treatment of myopia and astigmatism

Myopic astigmatism is a prevalent condition that can be treated with spectacles, contact lenses, or laser refractive surgery. However, these treatment options have functional limitations at higher levels of refractive error. The toric implantable collamer lens is designed to treat a broad range of refractive error, generally up to -18 diopters with +1 to +6 diopters of astigmatism. Approval for a more limited treatment range of up to 15 diopters of myopia with +1 to +4 diopters of astigmatism is being sought in the US, where this device has not yet received marketing approval. Surgical correction of high-myopic astigmatism can be life-altering and allow people to participate in activities that were not previously feasible because of visual limitations. The toric implantable collamer lens is implanted behind the iris and in front of the natural crystalline lens. With earlier lens designs, it was necessary to create an iridectomy or iridotomy to prevent pupillary block. The newest toric implantable collamer lens model has a small central hole that is not visually noticeable. This eliminates the need to create a hole in the iris, thereby enhancing the safety of the procedure.

Keratectasia after treating presbyopia with INTRACOR followed by SUPRACOR enhancement

PURPOSE

To report a case of unilateral keratectasia after INTRACOR, which was followed by an additional excimer LASIK enhancement with a new presbyopia-correcting ablation profile.

METHODS

The non-dominant eye of a 49-year-old man with emmetropia was treated with the INTRACOR procedure using the Technolas femtosecond laser (Technolas Perfect Vision GmbH, Munich, Germany) for presbyopia. Neither eye had risk factors for keratectasia. Two years later, a presbyopia-correcting LASIK (SUPRACOR LASIK; Technolas Perfect Vision GmbH) enhancement was performed in the same eye because of deteriorated distance and near visual acuity.

RESULTS

The eye treated with INTRACOR followed by SUPRACOR LASIK developed marked keratectasia topographically limited to the area altered by INTRACOR, whereas the fellow eye remained stable and still has no signs of keratoconus.

CONCLUSIONS

This case emphasizes the incomplete knowledge of the risk factors for keratectasia following INTRACOR alone and in combination with a SUPRACOR LASIK enhancement. It also suggests that the combined weakening effect of both procedures on corneal mechanical stability may be too strong even in the absence of established risk factors for LASIK surgery.

Ocular higher-order aberration features 10 years after photorefractive keratectomy

The aim of the present study is to re-evaluate the original cohort of patients who participated in the first photorefractive keratectomy (PRK) trial in the 1990s, especially their optical performance. Forty-four eyes (24 patients) of the original cohort who underwent PRK using the NIDK EC-5000 excimer laser platform returned 10 years (range 9-14 years) postoperatively to have higher-order aberrations (HOAs) recorded. Wavefront aberrations were measured using Wavescan (VISX, Santa Clara, CA, USA) and calculated for 3- and 6-mm pupil size. The total RMS (the square root of the sum of squared Zernike coefficients) of higher-order wavefront error (3rd-6th radial order) and the Zernike coefficients, as well as the third-order (S 3) and fourth-order (S 4) aberrations, spherical aberrations and coma aberration values were analyzed. An independent sample t test was used for comparisons and a P value <0.05 was considered statistically significant. The mean RMS of higher-order wavefront values showed an increase but no significant difference in postoperative eyes compared to the control-matched normal level with the 6-mm pupil (HOA RMS: control group 0.31 ± 0.12 μm; 10-year post-PRK group 0.56 ± 0.15 μm; P = 0.141). The main contribution was the increase of spherical aberrations (Z 12) and spherical-like aberrations (S 4), which increased by fourfold and 2.5-fold, respectively, in the 10-year post-PRK group (control group Z 12 0.08 ± 0.11 μm, S 4 0.14 ± 0.05 μm; 10-year post-PRK group Z 12 0.35 ± 0.15 μm, S 4 0.37 ± 0.14 μm; P = 0.010*). Most increases of ocular HOAs induced by corneal refractive surgery are becoming extremely minor at 10 years postoperatively, closer to the corresponding preoperative amount. The largest increase was spherical and spherical-like aberrations, especially with a larger pupil size.

Corneal flap morphological analysis using anterior segment optical coherence tomography in laser in situ keratomileusis with femtosecond lasers versus mechanical microkeratome

AIM

To assess and compare the flap morphology using anterior segment optical coherence tomography (AS-OCT) in laser in situ keratomileusis (LASIK) with Femto LDV femtosecond lasers versus Hansatome mechanical Microkeratome.

METHODS

AS-OCT (Visante) was used to compare 1 month postoperatively the morphology of the flaps created with Femto LDV femtosecond lasers or Hansatome Microkeratome. The intended flap thickness was 110µm and 160µm respectively. The thickness of twenty-five points across each flap, which were 0mm, 1.5mm, 2.5mm, and 3.5mm to the corneal vertex on the horizontal, vertical, 45° and 135° meridian respectively, was evaluated.

RESULTS

One month postoperative, the central flap thickness in the Femto LDV group was 107.43±4.70µm, while 125.90±17.50µm in the Hansatome group. The difference between the actual and the expected flap thickness was 5.61±3.84µm and 31.52±12.27µm, respectively. The Hansatome group had presented a statistically significant result (P<0.001). Flap morphology showed a more regular planar shape in the Femto LDV group and a meniscus shape in the Hansatome group.

CONCLUSION

AS-OCT is a direct and fast procedure to assess the flap morphology. The morphology by AS-OCT showed that the flaps created with Femto LDV femtosecond laser were more accurate and regular than the flaps created with Hansatome microkeratome.

Corneal elevation topography: best fit sphere, elevation distance, asphericity, toricity, and clinical implications

PURPOSE

To describe the effect of the corneal asphericity and toricity on the map patterns and best fit sphere (BFS) characteristics in elevation topography.

METHODS

The corneal surface was modeled as a biconic surface of principal radii and asphericity values of r1 and r2 and Q1 and Q2, respectively. The apex of the biconic surface corresponded to the origin of a polar coordinates system. Minimization of the squared residuals was used to calculate the values of the radii of the BFSs and apex distance (A-values: z distance between the corneal apex and the BFS) of the modeled corneal surface for various configurations relating to commonly clinically measured values of apical radius, asphericity, and toricity.

RESULTS

Increased apical radius of curvature and increased prolateness (negative asphericity) led to an increase in BFS radius but had opposite effects on the A-value. Increased prolateness resulted in increased BFS radius and A-value. Increasing toricity did not alter these findings. Color-plot elevation maps of the modeled corneal surface showed complete ridge patterns when toricity was increased and showed incomplete ridge and island patterns when prolateness was increased.

CONCLUSIONS

High A-values in patients with corneal astigmatism may result from steep apical curvature and/or high prolateness (negative asphericity). The BFS radius may help in distinguishing between these 2 causes of increased A-values. Increased prolateness and decreased apical radius of curvature (often seen in keratoconus) have opposite effects on the BFS radius but similar effects on the apex distance.

Corneal ectasia after LASIK despite low preoperative risk: tomographic and biomechanical findings in the unoperated, stable, fellow eye

PURPOSE

To report a case of progressive corneal ectasia after LASIK with no detectable preoperative risk factors and to present three-dimensional corneal tomographic and biomechanical findings on the contralateral unoperated eye that would be considered low risk for ectasia and thereby a good LASIK candidate based on the Randleman Ectasia Risk Score System (ERSS).

METHODS

A case report, literature review, and description of novel screening criteria based on Pentacam (Oculus Optikgeräte GmbH) corneal tomography are presented as well as Ocular Response Analyzer (ORA, Reichert Instruments) corneal biomechanical analysis.

RESULTS

Progressive corneal ectasia after LASIK of the operated left eye was confirmed by corneal topography. Scheimpflug imaging identified a meniscus-shaped LASIK flap with a central thickness of 165 μm and residual stromal bed thickness of 280 μm. Randleman ERSS score was 2 for the ectatic eye before LASIK and 1 for the current status of the unoperated eye, which remained stable with normal topography and no change in refraction for >5 years. Low corneal hysteresis (8.6 mmHg) and corneal resistance factor (7.5 mmHg) were found in the unoperated, nonectatic eye, along with a suspicious waveform sign of a second rebounded peak after second applanation. Pentacam average pachymetric progression was 1.09 (normal is <1.15); the Belin-Ambrósio overall deviation index was 1.99 (normal is <1.9).

CONCLUSIONS

Three-dimensional corneal tomographic and ORA biomechanical measurements provide additional information that may help identify individuals at high risk for naturally occurring or iatrogenic corneal ectasia.

Thin-flap laser-assisted in situ keratomileusis

PURPOSE OF REVIEW

Concerns regarding the increasing incidence of corneal ectasia following laser in situ keratomileusis procedures, together with increased understanding of the biomechanics of the cornea, has resulted in many refractive surgeons returning to surface ablation techniques such as photorefractive keratectomy. Even if surface ablation techniques offer a higher degree of safety than LASIK, they are associated with more pain and a slower visual recovery in the immediate postoperative period. This highlights the need for alternative procedures that offer the combined advantages of laser in situ keratomileusis and photorefractive keratectomy.

RECENT FINDINGS

Sub-Bowman's keratomileusis is a new procedure that provides the biomechanical stability and associated safety of photorefractive keratectomy with the visual results and reduced pain experience of laser in situ keratomileusis. This technique involves the use of the femtosecond laser to create a customized corneal flap of between 90 and 110 mum with a diameter based on the requirements of the individual patient and the type of excimer laser being used.

SUMMARY

This review outlines the rationale for sub-Bowman's keratomileusis and describes the efficacy, tolerability and safety of the procedure compared with photorefractive keratectomy.

Ten-year follow-up of laser in situ keratomileusis for high myopia

PURPOSE

To evaluate the long-term outcomes of laser in situ keratomileusis (LASIK) for high myopia.

DESIGN

A long-term (10 years) follow-up retrospective interventional case series study.

METHODS

The study included 196 myopic eyes of 118 patients with a mean preoperative spherical equivalent of -13.95 +/- 2.79 diopter (D) treated with myopic LASIK at the Instituto Oftalmológico de Alicante, Spain using the VISX 20/20 excimer laser (VISX Inc, Santa Monica, California, USA) and the Automated Corneal Shaper microkeratome (Chiron Vision, Irvine, California, USA). All patients were evaluated three months, one year, two years, five years, and 10 years postoperatively. The main outcome measures were refractive predictability and stability, mean corneal keratometry, topographical cylinder, safety, efficacy, stability of visual acuity, and postoperative complications.

RESULTS

At 10 years, 82 (42%) of 196 eyes were within +/-1.00 D and 119 (61%) were within +/-2.00 D. Fifty-four (27.5%) eyes underwent retreatments attributable to under correction and/or regression. The myopic regression decreases with time in eyes that did not undergo retreatment with a mean rate of -0.25 +/- 0.18 D per year. Eleven eyes (5%) lost more than 2 lines of best spectacle-corrected visual acuity (BSCVA) and 78 eyes (40%) showed a postoperatively uncorrected visual acuity of 20/40 or better. Two eyes (1%) with more than 15 D myopic correction developed corneal ectasia.

CONCLUSIONS

LASIK for myopia over -10 D is a safe procedure with myopic regression that slows down with time and a high rate of BSCVA increase in the long-term.

Analysis of ectasia after laser in situ keratomileusis: Risk factors

PURPOSE

To examine a database of laser in situ keratomileusis (LASIK) procedures for preoperative and operative factors assumed to increase the risk for developing post-LASIK ectasia.

SETTING

Private clinical practice.

METHODS

A computer database was queried for eyes that had LASIK for myopic refractive errors with the following characteristics: preoperative corneal thickness 500 microm or less, mean keratometry greater than 47.0 diopters (D), patient age 25 years or younger, attempted correction greater than -8.0 D, refractive astigmatism not with-the-rule and greater than 2.0 D, and residual stromal bed thickness (RST) 250 microm or less. Flap thickness and RST were measured using ultrasound pachymetry. All recorded information was exported to MS Excel and analyzed for eyes that had ectasia.

RESULTS

Of the 9700 eyes in the database, none with the above characteristics developed ectasia over mean follow-up periods exceeding 2 years. Seven eyes had multiple risk factors without ectasia. Three eyes with abnormal preoperative topography developed ectasia.

CONCLUSIONS

Individual preoperative and operative factors did not in and of themselves increase the risk for ectasia. Unmeasured and unknown factors that affect the individual cornea's biomechanical stability, in combination with some suspected risk factors as well as the current inability to identify corneas at risk for developing ectatic disorders, probably account for most eyes that develop ectasia today.