Agreement Between Autorefraction and Subjective Refraction in Keraring-Implanted Keratoconic Eyes

OBJECTIVES

To assess the agreement between subjective refraction and autorefraction and to explore the relationship between the magnitude of higher order aberration, and visual acuity and refraction, before and after keraring implantation.

METHODS

This prospective, randomized, interventional study enrolled 27 subjects (mean age 28.1±6.5 years) with keratoconus. Noncycloplegic refraction was performed subjectively by one clinician and with an autorefractor by another clinician, before and 6 months after surgery. The limit of agreement (LoA) between methods was assessed, and the relationships between the corrected distance visual acuity, logMAR on the one hand and refraction measurements and higher-order aberrations on the other, were examined.

RESULTS

The agreement in mean spherical equivalent refraction (MSER) between methods was good postoperatively but poor preoperatively. The autorefractor gave a more myopic refraction than subjective refraction preoperatively (-3.28±3.06 D; LoA -9.27 to +2.71 D, P<0.0001) and postoperatively (-0.63±1.64 D; LoA -3.85 to +2.58 D, P=0.055), and returned higher negative cylinders preoperatively (-1.10±1.17 D; LoA -3.40 to +1.19 D, P<0.0001) and postoperatively (-1.08±1.27 D; LoA -3.60 to +1.41 D, P<0.0001) in keratoconic eyes. The difference in MSER between methods was significantly related to the refractive error at both visits (P<0.05) and to the magnitude of higher-order aberrations in keratoconic eyes preoperatively (P<0.05). The logMAR visual acuity achieved subjectively worsened as the magnitude of higher-order aberrations increased preoperatively (P<0.001).

CONCLUSIONS

The autorefractor returns values that are significantly more myopic in MSER and higher negative cylinders than subjective refraction, preoperatively, but the MSER was similar between devices postoperatively. The autorefactor seems a valid starting point for subjective refraction in keratoconic eyes treated with keraring, but the cylinder should be corrected by about +1 D. The instruments agree more in less myopic than high myopic eyes.

Factors influencing the reliability of autorefractometry after LASIK for myopia and myopic astigmatism

PURPOSE

To study the factors influencing the reliability (accuracy) of autorefractometry before and after laser in situ keratomileusis (LASIK) for myopia and myopic astigmatism.

DESIGN

Retrospective case series.

METHODS

A total of 250 consecutive eyes (132 patients, mean age 37 years) were included from the Department of Ophthalmology, J.W. Goethe University, Frankfurt, Germany. The mean preoperative spherical equivalent of the subjective refraction (SR) was -6.59 diopters (D) (-1.38 to -15.13). The patient data were reviewed before and 1 month after LASIK, including SR, objective automated refraction (AR), and visual acuity. Subgroup analysis was performed with regard to the preoperative myopia and the excimer laser optical zone (OZ). The Holm-Sidak and Wilcoxon matched-pairs tests were used for statistical analysis.

RESULTS

The correlation coefficient between AR und SR is r = 0.98 before LASIK versus r = 0.79 afterwards (P < .001). The mean difference between the spherical equivalents (DSE) is +0.13 ± 0.51 D preoperatively versus -0.30 ± 0.58 D after LASIK (P < .001). With a small optical zone size (5.0-5.5 mm) the postoperative difference is -0.61 D, versus -0.36 D for OZ 5.6-6.0, versus -0.16 for OZ 6.1-7.0 mm. With a rising preoperative amount of myopia, the postoperative AR results become increasingly more myopic than the SR.

CONCLUSIONS

Following LASIK, autorefractometry is less accurate than in nonoperated eyes. The reliability of the AR is influenced by the OZ and the preoperative amount of myopia, with a small OZ and high myopia resulting in a greater difference between AR and SR and with the AR determining more myopic results.

Contact lens overrefraction variability in corneal power estimation after refractive surgery

PURPOSE

To evaluate the accuracy and precision of the contact lens overrefraction (CLO) method in determining corneal refractive power in post-refractive-surgery eyes.

SETTING

Refractive Surgery Service and Contact Lens Service, University of Illinois, Chicago, Illinois, USA.

METHODS

Fourteen eyes of 7 subjects who had a single myopic laser in situ keratomileusis procedure within 12 months with refractive stability were included in this prospective case series. The CLO method was compared with the historical method of predicting the corneal power using 4 different lens fitting strategies and 3 refractive pupil scan sizes (3 mm, 5 mm, and total pupil). Rigid lenses included 3 9.0 mm overall diameter lenses fit flat, steep, and an average of the 2, and a 15.0 mm diameter lens steep fit. Cycloplegic CLO was performed using the autorefractor function of the Nidek OPD-Scan ARK-10000. Results with each strategy were compared with the corneal power estimated with the historical method. The bias (mean of the difference), 95% limits of agreement, and difference versus mean plots for each strategy are presented.

RESULTS

In each subject, the CLO-estimated corneal power varied based on lens fit. On average, the bias between CLO and historical methods ranged from -0.38 to +2.42 diopters (D) and was significantly different from 0 in all but 3 strategies. Substantial variability in precision existed between fitting strategies, with the range of the 95% limits of agreement approximating 0.50 D in 2 strategies and 2.59 D in the worst-case scenario. The least precise fitting strategy was use of flat-fitting 9.0 mm diameter lenses.

CONCLUSIONS

The accuracy and precision of the CLO method of estimating corneal power in post-refractive-surgery eyes was highly variable on the basis of how rigid lense were fit. One of the most commonly used fitting strategies in clinical practice--flat-fitting a 9.0 diameter lens-resulted in the poorest accuracy and precision. Results also suggest use of large-diameter lenses may improve outcomes.

A return to primitive practice? Radial keratotomy revisited

Recently, a refractive surgeon was quoted in the national and professional press as proposing that radial keratotomy (RK) is to be preferred over laser procedures, such as photorefractive keratectomy (PRK) and laser assisted in situ keratomileusis (LASIK). The rationale for this public recommendation was that the RK procedure achieves better visual results and fewer complications than the laser procedures. Peer reviewed literature on these refractive procedures was surveyed to establish the validity of such a statement and it was found that current data do not support the notion that RK results in better visual outcomes than PRK and LASIK The true incidence of complications is difficult to establish. However, when the post procedure chronic effects are compared between RK, PRK and LA SIK, it becomes apparent that the post-RK patient pays the highest price, by a large margin, in visual quality impairment and corneal health. Although the visual acuity outcomes for low to moderate myopes, when corrected by any of the three refractive procedures considered here, are not dramatically different, we concluded that RK is not the preferred methodology because of its associated chronic visual and corneal health complications.

Repeatability of autorefraction and axial length measurements after laser in situ keratomileusis

PURPOSE

To assess the repeatability and agreement of refractive error measurements and the repeatability of axial length (AL) measurements in patients after laser in situ keratomileusis (LASIK).

SETTING

The Ohio State University College of Optometry, Columbus, Ohio, USA.

METHODS

Subjective refraction, autorefraction measurements with the Grand Seiko and Humphrey autorefractors, and AL measurements with the IOLMaster were completed for 40 previously myopic LASIK patients under noncycloplegic and cycloplegic conditions on 2 separate occasions.

RESULTS

The mean difference between visits for axial length measurements was 0.008 mm +/- 0.04 (SD). The between visits repeatability for all refractive error measurements were <0.75 diopter (D). The mean difference between the subjective refraction and the Humphrey autorefractor for spherical equivalent was statistically significant under noncycloplegic conditions (-0.90 D, P<.0001) and cycloplegic conditions (-2.05 D, P<.0001). The mean difference between subjective refraction and Grand Seiko autorefraction measurements was not significant under noncycloplegic conditions (+0.05 D, 95% limits of agreement [LoA]=-0.99, 1.09; P=.52) conditions but was statistically significant, but not clinically relevant, under cycloplegic conditions (+0.17 D, 95% LoA=-0.73, 1.07; P=.03).

CONCLUSIONS

Refractive error measurements after LASIK using the Grand Seiko autorefractor are reliable and agree well with subjective refraction measurements.

Autorefractometry after laser in situ keratomileusis

PURPOSE

To correlate cycloplegic subjective refraction with cycloplegic autorefractometry in eyes that have had laser in situ keratomileusis (LASIK).

SETTING

Vlemma Eye Institute, Athens, Greece.

METHODS

Subjective refraction and autorefractometry under cycloplegia were performed in 73 eyes of 46 patients 1, 6, and 12 months after LASIK to correct myopia or myopic astigmatism. The preoperative subjective refraction and autorefractometry under cycloplegia in the same eyes served as controls.

RESULTS

A statistically significant difference between subjective refraction and autorefraction was found in the sphere and cylinder at all postoperative times. No statistically significant difference was found in the axis. There was no statistically significant difference in the control eyes.

CONCLUSIONS

Automated refractometry in eyes that had had LASIK was reliable in the axis only. Retreatments after LASIK should always be based on subjective refraction.

Correlation Between Automated and Subjective Refraction Before and After Photorefractive Keratectomy

PURPOSE

To ascertain whether autorefractometry after photorefractive keratectomy (PRK) provides results that are comparable with subjective refractometry.

METHODS

The refractions of 159 eyes before and 1 month after PRK were determined with both automated and subjective refractometry, and the results of the two methods were compared.

RESULTS

Before PRK, subjective spherical equivalent refraction ranged from -15.25 to +0.25 D (mean -5.30 +/- 2.64 D) and automated spherical equivalent refraction ranged from -16.13 to -0.50 D (mean -6.10 +/- 2.74 D), with good correlation (r2 = 0.965) between the two methods. One month after PRK, subjective spherical equivalent refraction ranged from -1.63 to +3.50 D (mean +0.98 +/- 0.78 D) and automated spherical equivalent refraction ranged from -2.50 to +3.00 D (mean +0.36 +/- 0.96 D) with poor correlation (r2 = 0.401).

CONCLUSION

Autorefractometry is less reliable in eyes after PRK, and consequently software changes are recommended for overcoming this problem.

Comparison of objective and subjective refraction before and after laser in situ keratomileusis

PURPOSE

To compare the accuracy and reliability of objective and subjective refractions before and after laser in situ keratomileusis (LASIK) for myopia, hyperopia, and astigmatism.

SETTING

Augenchirurgie und Laserzentrum Hochrum, Innsbruck, Austria.

METHODS

In this prospective study, the objective refraction obtained with the Nidek AR-K 900 autorefractor was compared with the subjective refraction in 159 eyes (125 with myopia and 34 with hyperopia) operated on with 2 different lasers. Refractions were done before and 6 months after LASIK.

RESULTS

Preoperatively, the objective and subjective refractions correlated better in eyes with low myopia than in those with high myopia (P < .01). Postoperatively, objective refraction was less accurate and reliable than preoperatively. The difference between the objective and subjective spherical refractions was statistically significant (P < .0001) after LASIK in eyes with hyperopia. The correlation between the objective and subjective cylindrical refractions was stronger preoperatively. Especially after LASIK for hyperopia, the objective refraction did not reliably assess the magnitude and axis of the cylinder. The preoperative refractive error did not significantly affect the preoperative and postoperative difference between the objective and subjective refractions or the change between the preoperative and postoperative mean differences. The type of excimer laser used significantly affected the difference between the objective and subjective refractions.

CONCLUSIONS

Especially after LASIK for hyperopia, the objective refraction determined with the Nidek AR-K 900 autorefractor delivered erroneous results, which have implications for postoperative care and preoperative measurements for ocular surgery such as enhancement procedures or cataract surgery.