Optical biometry before and after excimer laser epithelial keratomileusis (LASEK) for myopia

Unexpected ocular morphological changes after corneal refractive surgery: A review

Corneal refractive surgery (CRS) currently is widely used to correct refractive errors because of its efficacy and reliability. Several studies dealt with the corneal modification induced by this type of surgery, but it is still debated if CRS can induce unexpected changes namely anterior chamber depth (ACD) and axial length (AL). A literature review was performed, including all articles regarding CRS and eye-variations from 1999 to December 2021. Excluding articles about specific systemic conditions (e.g., pregnancy), pathological conditions, post-surgical complications or about only corneal flattening and thinning post CRS, we found nine studies that met the search criteria. We divided the found articles according to the type of surgery performed (radial keratotomy, PRK/LASEK, lasik) and analyzed the results about ACD and AL. Finally, according to the literature, we can conclude that CRS not only gives a corneal flattening, thinning and biomechanical changes, but also induces AL and ACD decrease. This makes the AL and ACD measurements obtained before CRS uselessness in case of IOL power calculation.

Outcomes and eye care knowledge in rhegmatogenous retinal detachment patients with a history of laser refractive surgery for myopia

Purpose

To investigate the surgical outcomes and eye care knowledge of patients with rhegmatogenous retinal detachment (RRD) who had previously undergone laser refractive surgery (LRS) for myopia in a myopia epidemic area.

Methods

This retrospective study included patients with primary RRD who underwent surgery and had a history of LRS for myopia at a tertiary medical center. Data were reviewed from medical charts to analyse the surgical outcomes. Questions about eye care knowledge and attitude toward myopia and LRS were obtained.

Results

A total of 774 patients underwent RRD surgery, among whom 341 (44%) had myopia > -3 dioptres, 66% of whom had high myopia. Thirty eyes of 26 patients had a history of LRS for myopia. The mean age of patients with a history of LRS was significantly lower than that of those without a history of LRS (45.7 ± 2.9 years vs. 53.8 ± 1.0, p < 0.001). The mean pre-LRS spherical equivalent was -8.66 ± 0.92 (range: -3.00--12.00) dioptres. In more than half the patients (n = 15, 57.7%), the interval between LRS and RRD was more than 10 years. The primary retinal reattachment rate was only 60%, whereas the final retinal reattachment rate was 93%. The mean final visual acuity (VA) improved from a 20/286 to 20/105 (p = 0.006). Linear mixed model analysis showed factors of male sex and macular detachment were significant with poor visual outcome (p = 0.046 and 0.008) Eye care knowledge obtained from the 19 RRD patients with history of LRS, 47% of patients (9/19) mistakenly thought that LRS could cure myopia and its complications, and 63% of patients were less willing to visit an ophthalmologist because uncorrected VA improvement after LRS. Eighty-four percent thought that proper knowledge and more education about LRS and myopia for the public are important.

Conclusion

In the RRD patients with a history of LRS for myopia, their age was relative younger. Male sex and macular detachment were associated with poor visual outcome. More education with proper knowledge of LRS, myopia and RRD is recommended for the patients to prevent or early detect the occurrence of RRD.

Cataract surgery on the previous corneal refractive surgery patient

Cataract surgery in cases with previous corneal refractive surgery may be a major challenge for the ophthalmologist. The refractive outcome of the case deserves special attention in the preoperative planning process, which should be tailored for the type of prior refractive procedure: incisional, ablative under a flap, or on the corneal surface. Avoiding refractive surprise after cataract surgery in these cases is principally dependent on the accuracy of the intraocular lens calculation, together with the selection of the appropriate biometric formula for each case. Modern techniques for cataract surgery help surgeons to move toward the goal of cataract surgery as a refractive procedure free from refractive error. We give practical guidelines for the cataract surgeon in the management of these challenging cases.

Assessment of axial length before and after myopic LASIK with the IOLMaster

PURPOSE

To assess the relationship between theoretical ablation depth and axial length change after LASIK with the IOLMaster (Carl Zeiss Meditec, Dublin, CA).

METHODS

Ninety-nine eyes were examined preoperatively and 1 and 3 months after LASIK.

RESULTS

Mean ± standard deviation (SD) spherical equivalent before LASIK was -4.06 ± 1.91 diopters (D). Mean ± SD ablation depth was 83.13 ± 30.31 μm. Mean ± SD postoperative axial length of 25.11 ± 0.14 mm at 1 month was significantly shorter than mean ± SD preoperative axial length of 25.20 ± 0.14 mm (P < .001) with no subsequent change thereafter (P = .450). An increase in ablation depth of 1 μm led to a decrease in axial length of 0.00118 ± 0.00005 mm. Ablation depth correlated strongly with change in axial length (adjusted R(2) = 0.9039).

CONCLUSIONS

The IOLMaster showed a decrease in axial length after LASIK that correlated well with theoretical ablation depth.

Axial eye length measurements pre-and post-laser-assisted in situ keratomileusis using the IOL Master: a pilot study

Purpose

A preliminary study in order to test the accuracy of the IOL Master in detecting axial eye length changes after laser-assisted in situ keratomileusis and to correlate the findings with the theoretical ablation depth.

Methods

Pre-and postoperative axial eye length measurements were performed in 10 consecutive eyes that underwent laser-assisted in situ keratomileusis with the Alcon Ladar Vision excimer laser to treat myopic refractive errors ranging from −2.50 to −8.00 diopters of spherical equivalent (mean: −5.23 ± 1.30 D).

Results

The preoperative axial eye length measurements ranged from 24.53 mm to 27.78 mm (mean: 25.80 ± 1.01 mm) and from 24.57 mm to 27.57 mm (mean: 25.68 ± 0.93 mm) 1 month after the operation. Preoperative and 1-month postoperative data showed a statistically significant difference (P < 0.05).

Conclusions

The IOL Master showed a decrease in the axial eye length measurements that was bigger than the theoretical ablation depth and did not correlate well with it. Such data need to be confirmed by a larger cohort of patients.

Intraocular lens power calculation after corneal refractive surgery

Cataract surgery after corneal refractive surgery can be challenging for the ocular surgeon due to the difficulty with accurate intraocular lens (IOL) power determination and unexpected refractive surprises. As clinicians have done more work, a number of error sources have been determined. Furthermore, an increasing number of methods to avoid these refractive surprises have been proposed. The combination of this work has resulted in recommendations for the modification of standard IOL power calculations to improve outcomes. The following article includes a brief on, and by no means, inclusive, error sources and ways to compensate for them.

A regression model for correcting intraocular lens power after refractive surgery independent of preoperative data

PURPOSE

To find a method of calculating intraocular lens (IOL) power that may be independent of preoperative data in eyes that have previously undergone myopic laser in situ keratomileusis (LASIK).

METHODS

In 148 eyes of 75 patients, before and 6 months after LASIK, IOL power was calculated with SRK/T formula utilizing the spherical equivalent as the desired target refraction. Assuming that LASIK does not alter the crystalline lens refractive properties, IOL calculation error (CER) was estimated with this formula: CER = [pre-LASIK IOL power]/[post-LASIK IOL power]. Then the authors used postoperative biometry and Orbscan II corneal topography data in multiple regression models to find the best variables to predict the CER. Predicted amount of error which is calculated independent of preoperative data could be used to correct the post-LASIK calculated IOL: [corrected post-LASIK IOL power] = CER x [post-LASIK IOL power].

RESULTS

A regression model with these predictors was found: axial length in millimeters (L), radius of the anterior corneal surface best fitted sphere in millimeters divided by radius of the posterior corneal surface best fitted sphere in millimeters (AntBFS/PostBFS), corneal central 5 millimeters mean power in diopters divided by corneal central 3 millimeters mean power in diopters (mean 5 mm/mean 3 mm), the post-LASIK IOL power, and the post-LASIK simulated K reading. The model R square was 0.88.

CONCLUSIONS

There is correlation between post-LASIK biometry values and IOL power correction factor. This study presents a new model for further investigation.

Intraocular Lens Power Calculation after Myopic Refractive Surgery

OBJECTIVE

To evaluate the reliability of different methods developed to calculate intraocular lens (IOL) power after corneal refractive surgery.

DESIGN

Retrospective observational case series.

PARTICIPANTS

Preoperative and postoperative data of all eyes that underwent myopic excimer laser surgery in a private practice (Centro Salus, Bologna, Italy) between 1999 and 2004 were reviewed.

INTERVENTION

The following methods were analyzed: videokeratography, clinical history, Shammas' refraction-derived and clinically derived methods, Rosa's correcting factor, Ferrara's variable refractive index, separate consideration of anterior and posterior corneal curvature (with and without preoperative data), Feiz-Mannis' formula and nomogram, and Latkany's regression formulas (based on both average and flattest postrefractive surgery keratometry). The Holladay 1 formula was used for eyes with an axial length between 22 and 24.49 mm and the SRK-T for eyes longer than 24.49 mm. Double-K formulas were also evaluated, when applicable. Each IOL power determined with these methods was compared to a benchmark value, calculated using the preoperative axial length and corneal power and aiming for the preoperative spherical equivalent.

MAIN OUTCOME MEASURE

Mean error in IOL power prediction.

RESULTS

Ninety-eight eyes of 98 patients were analyzed. The double-K clinical history method, Feiz-Mannis' formula, double-K method based on separate consideration of anterior and posterior corneal curvature (with and without preoperative data), and both Latkany's regression formulas were the only methods resulting in a mean IOL power not statistically different (P>0.05) from the benchmark used for comparative purposes.

CONCLUSIONS

When prerefractive surgery data are available, IOL power should be calculated using the double-K clinical history method. Alternative choices may be represented by the Feiz-Mannis' formula, Latkany's regression formulas based on average and flattest postrefractive surgery keratometry, and the double-K method based on separate consideration of anterior and posterior corneal curvatures. A variant of the latter can be used to calculate IOL power when prerefractive surgery data are not available. Further prospective studies based on patients undergoing phacoemulsification after refractive surgery are needed to validate the results of this theoretical comparison.

Axial Eye Length Evaluation Before and After Myopic Photorefractive Keratectomy

PURPOSE

To test the accuracy of a new device (IOL Master; Carl Zeiss, Jena, Germany) in detecting axial eye length changes after photorefractive keratectomy (PRK).

METHODS

Pre- and postoperative (1, 3, and 6 months) subjective refraction and axial eye length measurements were performed in 184 consecutive eyes that underwent PRK with the Nidek EC5000 excimer laser (Nidek Technologies, Gamagori, Japan) to treat refractive errors from +0.25 to -16.25 diopters (D) (mean: -5.12 +/- 3.01 D).

RESULTS

The axial eye length measurements ranged from 22.51 to 31.32 mm (mean: 25.61 +/- 1.47 mm) before PRK; from 22.39 to 31.10 mm (mean: 25.48 +/- 1.43 mm) 1 month after PRK; from 23.17 to 31.14 mm (mean: 25.61 +/- 1.36 mm) 3 months after PRK; and from 23.36 to 29.68 mm (mean: 25.58 +/- 1.35 mm) 6 months after PRK. Preoperative and 1-month postoperative data showed a statistically significant difference (P<.001), whereas no significant difference was found between 1 and 3 months (P=.0137) or 3 and 6 months (P=.2422).

CONCLUSIONS

The IOL Master showed a decrease in the axial eye length measurement larger than the theoretical ablation depth and the difference increased as the correction became higher.