Diurnal change in refraction, corneal curvature, visual acuity, and intraocular pressure after radial keratotomy in the PERK Study

BCLA CLEAR Presbyopia: Evaluation and diagnosis

It is important to be able to measure the range of clear focus in clinical practice to advise on presbyopia correction techniques and to optimise the correction power. Both subjective and objective techniques are necessary: subjective techniques (such as patient reported outcome questionnaires and defocus curves) assess the impact of presbyopia on a patient and how the combination of residual objective accommodation and their natural DoF work for them; objective techniques (such as autorefraction, corneal topography and lens imaging) allow the clinician to understand how well a technique is working optically and whether it is the right choice or how adjustments can be made to optimise performance. Techniques to assess visual performance and adverse effects must be carefully conducted to gain a reliable end-point, considering the target size, contrast and illumination. Objective techniques are generally more reliable, can help to explain unexpected subjective results and imaging can be a powerful communication tool with patients. A clear diagnosis, excluding factors such as binocular vision issues or digital eye strain that can also cause similar symptoms, is critical for the patient to understand and adapt to presbyopia. Some corrective options are more permanent, such as implanted inlays / intraocular lenses or laser refractive surgery, so the optics can be trialled with contact lenses in advance (including differences between the eyes) to better communicate with the patient how the optics will work for them so they can make an informed choice.

The VRF-L and VRF-GL IOL power calculation methods after radial keratotomy

BACKGROUND

To investigate the accuracy of the VRF-L and VRF-GL IOL power calculation methods in cataract surgery after radial keratotomy (RK).

METHODS

The VRF-L and VRF-GL methods were collated with nine formulas: Barrett True K (No History), Haigis, Hoffer Q, Hoffer Q (Double-K), Holladay 1 (Double-K), Holladay 2 (Double-K), PEARL-DGS (RK), SRK/T (Double-K), and T2 (Double-K). With SS-OCT biometry (IOLMaster 700, Carl Zeiss Meditec), data of 78 eyes from 78 patients with previous RK was included. Optimised lens constants were sourced from the IOL Con website. Subjective refraction was obtained at 4 to 5 months postoperatively. The root mean square absolute error (RMSAE) and median absolute error (MedAE) were chosen as primary outcomes and the percentage of eyes with PEs within ±0.25 D, ±0.50 D, ±0.75 D, and ±1.00 D were analysed.

RESULTS

Statistical significance (Bootstrap-t test, P < 0.05) was shown by VRF-GL, VRF-L, and Haigis formulas with the lowest RMSAE (0.813 D, 0.816 D and 0.824 D) and MedAE (0.511 D, 0.497 D and 0.533 D) values. The Barrett True K formula was less predictable (0.836 and 0.580, respectively). The VRF-L, VRF-GL, and Haigis achieved the highest percentage of eyes with a PE within ±0.50 D (52.56%, 50.00%, and 46.15%) and ±1.00 D (79.49%, 79.49%, and 80.77% respectively).

CONCLUSION

The VRF-L and VRF-GL methods demonstrated higher accuracy and were comparable with existing methods in eyes after RK. The Haigis was an alternative option with a higher percentage of eyes with a PE within ±1.00 D (80.77%).

"Rapid and reversible alteration in corneal contour and power associated with Netarsudil/Latanoprost"

Purpose

To describe a previously unreported case of reversible myopic shift with corresponding changes in corneal contour in a patient treated with netarsudil/latanoprost.

Observations

A 72-year-old male with history of primary open angle glaucoma, prior cataract surgery, and remote radial keratotomy surgery was treated with fixed-dose combination of netarsudil/latanoprost. Despite no prior history of refractive shift in the twenty years since radial keratotomy surgery, on one month follow-up, he reported reduced visual acuity and presented with approximately 1.50 D shift in both eyes. There were associated corneal contour changes. No corneal epithelial bullae or edema were appreciated. Netarsudil/latanoprost was discontinued and timolol was initiated. One month later, both refractive error and corneal contour returned to prior levels.

Conclusions

Netarsudil is a rho-kinase and norepinephrine transporter inhibitor that may be effective in the treatment of primary open angle glaucoma resistant to other topical treatments. In addition to corneal epithelial bullous edema previously reported, this drug may induce reversible changes in corneal contour in patients with prior corneal or refractive surgery.

How a dynamic optical system maintains image quality: Self-adjustment of the human eye

The eyeball is continually subjected to forces that cause alterations to its shape and dimensions, as well as to its optical components. Forces that induce accommodation result in an intentional change in focus; others, such as the effect of intraocular pressure fluctuations, are more subtle. Although the mechanical properties of the eyeball and its components permit mediation of such subtle forces, the concomitant optical changes are not detected by the visual system. Optical self-adjustment is postulated as the mechanism that maintains image quality. The purpose of this study was to investigate how self-adjustment occurs by using an optical model of the eyeball and to test the requisite optical and biometric conditions.

Intraocular Lens Power Selection after Radial Keratotomy: Topography, Manual, and IOLMaster Keratometry Results Using Haigis Formulas

PURPOSE

To compare final spherical equivalent (SE) refractions in patients who previously underwent radial keratotomy (RK) undergoing routine cataract surgery using keratometry (K) values from the Tomey (Topographic Modeling System [TMS]; Tomey Corp., Phoenix, AZ) Placido topographer, manual keratometer, and IOLMaster (Carl Zeiss Meditec AG, Jena, Germany) keratometer using the Haigis formulas.

DESIGN

Retrospective case series.

SUBJECTS

A total of 26 RK eyes (20 patients) with a minimum of 3 months postoperative follow-up.

METHODS

The following K values were evaluated: TMS topography (flattest K within first 9 rings, average K, minimum K), manual K, IOLMaster K. The final refractive goal was -0.50 diopters (D) for all eyes. The Haigis formula with target refraction -0.50 D was used. In addition, because of observed hyperopic overcorrections, IOLMaster K with the Haigis formula set to -1.00 D but with a final refractive goal of -0.50 D was also tested. The Haigis-L formula using IOLMaster K values was separately evaluated.

MAIN OUTCOME MEASURES

Mean final SE refraction, percent final SE within ideal (-0.12 to -1.00 D), acceptable (0.25 to -1.50 D), or unacceptable (<-1.50 or >0.25 D) range and within ±0.50 D and ±1.00 D of the intended result.

RESULTS

Best results with minimal overcorrections were achieved with TMS flattest K (mean -0.68±0.60 D, 73% within ±0.50 D, and 88% within ±1.00 D of the surgical goal) and IOLMaster K set for target -1.00 D (mean -0.66±0.61 D, 69% within ±0.50 D, and 88% within ±1.00 D of the surgical goal). Other values produced more hyperopic (manual, IOLMaster K set for target -0.50 D, average topography) or higher myopic (minimum topography, Haigis-L) results.

CONCLUSIONS

For simplicity, using the IOLMaster K values combined with the Haigis formula set for target refraction -1.00 D produces acceptable results aiming for -0.50 D final SE refractions in former RK patients undergoing routine cataract surgery.

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.

Going to High Altitude with Preexisting Ocular Conditions

The goal of this paper is to review how preexisting ocular conditions may be affected by altitude exposure. Such preexisting conditions include dry eye problems, monocular visual loss, and potential problems following refractive surgery procedures, as well as the possible changes associated with some forms of retinal and optic nerve diseases. Although most such altitude-related visual difficulties are relatively minor, some have resulted in serious morbidity or even death at high altitude. This review will give the reader background regarding these potentially debilitating conditions in order to better prepare for exposure to high altitude environments.

Contact lens fitting for post-radial-keratotomy residual myopia

PURPOSE

To formulate guidelines for contact lens fitting following radial keratotomy and to achieve a relationship between contact lens fitting parameters and refractive and keratometric parameters.

METHODS

Thirty-five eyes of 30 patients who had post-radial-keratotomy residual myopia were evaluated for contact lens fitting. The base curve was selected by 'hit and trial' method until a proper fit was achieved, following which an over-refraction was done and final power of the contact lens obtained.

RESULTS

The mean contact lens base curve was 43.04 +/- 1.62 D, which was steeper than the postoperative keratometry by 2.35 +/- 0.74 D. The base curve and the postoperative keratometry were correlated by regression analysis (r = 0.895, P < 0.001). The mean overall diameter of the contact lenses was 9.64 +/- 0.08 mm. The mean contact lens power was 5.81 +/- 3.07 D, which was more myopic than the residual myopia by 2.79 +/- 1.67 D. Regression analysis showed definite correlation between the contact lens power and postoperative myopia (r = 0.854, P < 0.001).

CONCLUSION

For correction of post-radial-keratotomy residual myopia, contact lens fitting parameters can be determined by a regression formula using keratometric and refractive values.

Diurnal Variation of Human Corneal Curvature in Young Adults

PURPOSE

To elucidate the diurnal variation of human corneal curvature with regard to gender and menstrual cycle.

METHODS

Changes in corneal curvature and intraocular pressure (IOP) were measured over 24 hours in 14 young adults using corneal topography and a non-contact tonometer. In study 1, seven males and seven females (after menses) were measured. In study 2, four females out of the seven volunteers who participated in study 1 were measured again during menses.

RESULTS

The females after menses showed a remarkable diurnal variation throughout 24 hours. A significant difference between the light-wake periods and dark-sleep periods of 0.83 +/- 0.15 D was found (P < .01). Corneal curvature was significantly flatter during menses than after menses in the light-wake period (P < .05). In the males, no significant diurnal change (0.21 +/- 0.12 D) was measured in corneal curvature.

CONCLUSIONS

Diurnal variation of corneal curvature was significant, approximately 0.83 D in young females after menses, and corneal curvature became flatter during menses in young females. Diurnal variation of corneal curvature is an important parameter for planning refractive surgery and contact lens wear.

Epithelial plugs in radial keratotomy: the origin of incisional keratitis?

PURPOSE

Incisions in radial keratotomy (RK) patients were examined histopathologically to explore the cause of delayed infections occurring following this procedure.

METHODS

Four corneas from two successful RK patients were obtained postmortem and 1 cornea from an unsuccessful RK was collected following lamellar keratoplasty. The tissue was prepared for light and transmission electron microscopy.

RESULTS

All incisions examined contained an epithelial plug. The average depth of the plugs for left and right corneas in the 2 successful cases were 142.58 microm (range: 36.46-183.04 microm) and 58.44 microm (range: 29.27-115.66 microm), whereas the unsuccessful case these measurements were 121.06 microm (range: 70.03-172.01 microm). In the successful cases, the plugs were on average 4.2 cells deep (range: 2-5) in one case and for the other the plugs were 8.78 cells deep (range: 1.5-11.5) and 2.72 cells wide (range: 2-4). In the unsuccessful case the plugs were on average 6.89 cells deep (range: 5-11) and 8.56 cells wide (range: 4-13). The average epithelial thickness, measured 200 microm on either side away from the plug, was 47.11 microm and 55.09 microm for the successful cases, and 27.52 microm for the unsuccessful case. Degenerate cells were often observed within the plug and along the overlying surface. Lamellae cut during surgery remained severed in all corneas observed. The stroma adjacent to the incision contained an elevated number of stromal cells (8%-78%).

CONCLUSIONS

Healing did not include repair of anterior limiting lamina or stromal lamellae, which all remained severed in all incisions observed. Epithelial plugs were invariably present in all incisions regardless of clinical outcome, thus, increasing the distance a basal cell travels to reach the epithelial surface by 2 to 4 times. Since the epithelial cell has a limited life, it is hypothesized that cells originating in the plug may die before reaching the surface, thus, leading to intermittent loss of surface integrity. The loss of the epithelial barrier allows invasion of microorganisms and the delayed onset of keratitis. The larger the plug the greater the possibility of surface defects and resultant infection.

Two-year outcomes of intrastromal corneal ring segments for the correction of myopia

OBJECTIVE

To evaluate the safety and efficacy of Intrastromal Corneal Ring Segments (ICRS) for the correction of myopia.

DESIGN

Nonrandomized, comparative trial.

PARTICIPANTS

Patients enrolled in the United States Food and Drug Administration phase II and phase III clinical trials of the ICRS had best spectacle-corrected visual acuity (BSCVA) of 20/20 or better, myopia of -1.00 to -3.50 diopters (D), and a cylindrical correction of 1.00 D or less as measured by manifest refraction.

INTERVENTION

Surgical correction of myopia with an ICRS.

MAIN OUTCOME MEASURES

Efficacy was assessed by predictability of refractive outcome (deviation from predicted cycloplegic refraction spherical equivalent), stability of refractive effect, and postoperative uncorrected visual acuity. Safety was assessed by adverse events, maintenance or loss of preoperative BSCVA, and induced manifest refraction cylinder.

RESULTS

Four hundred fifty-two patients were enrolled at 11 investigational sites in both studies. Of the 454 surgical attempts, 449 received an ICRS in one eye (0.25, 0.30, and 0.35 mm in 148, 151, and 150 eyes, respectively). First surgeries were attempted in 452 patients. An ICRS was successfully implanted in 447 initial eyes, and 5 surgeries were discontinued. Of the five discontinued surgeries, three patients subsequently exited from the study, and two patients went on to have the ICRS implanted in the second eye, bringing the total number of successful implants to 449 patient eyes. Month 24 postoperative follow-up was completed on 358 patients (80%). At month 24, 328 of 354 eyes (93%) were within +/-1.00 D of predicted refractive outcome. Refraction changed by 1 D or less in 97% of eyes (421/435) between 3 and 6 months after implantation and in 99% (343/348) between months 18 and 24. Before surgery, 87% of eyes (390/448) saw worse than 20/40 uncorrected; 24 months after surgery, 55% of eyes (196/358) saw 20/16 or better, 76% (271/358) saw 20/20 or better, and 97% (346/358) saw 20/40 or better. Although two eyes (2/358; 0.5%) lost two or more lines of BSCVA at 24 months; visual acuity in both was 20/20 or better. Intraoperative complications included anterior corneal surface perforation (three eyes) and anterior chamber perforations (two eyes, one during an attempted exchange procedure); all healed spontaneously without suturing and without loss of BSCVA. The ICRS was repositioned in five eyes to increase correction. Postoperative complications in one eye each were infectious keratitis, shallow segment placement, and loss of two lines of BSCVA at two or more consecutive examinations (subsequently regained).

CONCLUSIONS

The ICRS safely, predictably, and effectively reduced or eliminated myopia of -1.00 to -3.50 D. The refractive effect was stable over time.

Minimizing radial-keratotomy-induced diurnal variation in vision using contact lenses

A 41-year-old man with 16 radial keratotomy (RK) incisions in each eye reported a paradoxical diurnal variation in vision in both eyes with low Dk/L soft contact lenses. After rk, the patient experienced the conventional diurnal change a morning-to-evening mean (right and left eyes) myopic change of -1.80 diopters (D). However, while wearing low Dk/L contact lenses, a paradoxical morning-to-evening mean hyperopic change of 2.30 D was found. The diurnal variation was minimized (0.50 D) by wearing high Dk/L contact lenses. These results suggest that contact lenses can be used to treat diurnal variation in manifest refraction after RK by inducing appropriate stress.

Diurnal stability of refraction after implantation with intracorneal ring segments

PURPOSE

To investigate diurnal changes in visual acuity and refraction in myopic eyes implanted with intracorneal ring segments (ICRS).

SETTING

University of California San Diego Shiley Eye Center, La Jolla, California, and Emory University Vision Correction Center, Atlanta, Georgia, USA.

METHODS

This prospective study involved 2 groups of patients who had ICRS (Intacs) implantation and a follow-up of at least 6 months. The first group included 102 eyes of 51 bilaterally treated patients; the second group, 32 eyes of 16 unilaterally treated patients. Examinations including visual acuity, manifest refraction, and videokeratography were done in the morning and evening at least 9 hours apart on a single day. Refractive changes were analyzed by power vectors; multivariate statistics were used to determine the significance of change in any component of the spectacle prescription.

RESULTS

In the bilateral treatment group, 97 eyes (95%) were within 1 line of spectacle-corrected visual acuity from morning to evening. The mean change in manifest refraction was -0.14 +0.08 x 4 and in spherical equivalent, -0.10 diopters (D) (sigma = 0.3; range -0.750 to +0.875 D). Ninety-six eyes (94%) had a change in refraction within 0.50 D of spherical equivalent. There was no significant change in corneal power (P =.20). In the unilateral treatment group, there was no significant difference between treated and untreated eyes in changes in spectacle-corrected visual acuity, manifest refraction, or corneal power and toricity (P.05).

CONCLUSION

No clinically significant diurnal variation in visual acuity or manifest refraction was observed after ICRS implantation or in untreated paired eyes. Moreover, the data suggest less diurnal change in visual acuity and refraction after ICRS implantation.

Diurnal fluctuations in corneal topography 10 years after radial keratotomy in the Prospective Evaluation of Radial Keratotomy Study

PURPOSE

To correlate clinically observed fluctuations in manifest refraction, visual acuity, keratometry, and intraocular pressure (IOP) with changes in the anterior corneal surface as measured by videokeratography in patients 10 years after radial keratotomy (RK).

SETTING

Four clinical centers in the United States that participated in the Prospective Evaluation of Radial Keratotomy (PERK) study.

METHODS

Thirty-two eyes of 20 PERK patients who noted diurnal fluctuations in vision had clinical examination and videokeratography (TMS-1, Computed Anatomy Inc.) in the morning and evening of the same day a mean of 10.3 years (range 7.8 to 11.7 years) after RK. The videokeratographs were analyzed in terms of various indexes generated by custom-designed software. Morning-to-evening changes in the means of the various clinical and videokeratographic values were assessed using pairwise methods.

RESULTS

The mean increase in myopia was 0.36 diopters (D) +/- 0.58 (SD) from morning to evening (P < .01). Analysis of the videokeratographs showed a corresponding increase in average corneal power (ACP), reflecting a steepening of 0.52 +/- 0.45 D (P < .001). The change in ACP was correlated with a change in the manifest spherical equivalent refraction (R = 0.39, P = .03) and a change in best spectacle-corrected visual acuity (R = 0.38, P = .03) over the same period. Similarly, simulated keratometry (SimK) readings correlated with the change in the manifest spherical equivalent refraction (R = 0.38, P = .03 for SimK1; R = 0.37, P = .35 for SimK2; R = 0.4, P = .02 for average SimK), although the standard clinical keratometric data did not (P = .26 for K1, P = .11 for K2, and P = .09 for the mean K). The elevation depression magnitude, a measure of the low-frequency irregularities of the cornea, showed a decrease of 0.32 +/- 1.59, which also correlated with the change in the manifest spherical equivalent refraction (R = 0.37, P = .04). Intraocular pressure tended to decrease from morning to evening (mean change of -0.97 +/- 3.29 mm Hg), but the difference was not significant. Variations in IOP in individual patients, however, were correlated with changes in the manifest spherical equivalent refraction (R = 0.37, P = .04).

CONCLUSIONS

Diurnal fluctuations in corneal topographic indexes can be used to evaluate the diurnal fluctuations in refraction and visual acuity after RK. The study findings provide statistical support for the idea that IOP contributes to the diurnal fluctuation in visual acuity after RK.

Orbscan pachymetry: implications of a repeated measures and diurnal variation analysis

INTRODUCTION

Corneal thickness changes reflect alterations in hydration and metabolism. Ultrasound pachymetry determinations may be adversely influenced by fluctuations in tissue hydration, whereas optical systems are apparently unaffected by these fluxes. A recently marketed, optical-based, topographic mapping system (Orbscan; Orbtek, Inc.) uses anterior and posterior corneal surface data to calculate corneal thickness.

OBJECTIVE

This new instrumentation presents as a potentially useful pachymetry tool for evaluation of corneas under hydration flux or challenge (e.g., postphotorefractive keratectomy [PRK] healing studies) and was therefore evaluated for accuracy and variability.

MEASUREMENTS

Three calibrated standards were measured in repeated fashion. Additionally, 1 test subject was measured 30 times in 1 day (5 measurements each at 8:00, 9:30, and 11:00 AM and at 1:00, 2:30, and 4:00 PM). Corresponding measurements were made at 8:00 and 11:00 AM and at 4:00 PM on 3 separate days to assess repeatability. Grouped data from 18 volunteer subjects were compared to the data of the test subject as well.

RESULTS

Pachymetry accuracy on a calibrated standard was determined to be +/-2 microm (standard deviation, n = 12). Repeated measures on the subject demonstrated a mean standard deviation of 9.08 microm for 750 thickness data points across the central 7 mm of the cornea; peripheral measurement points exhibited progressively greater variability than at the apex (analysis of variance; P<0.0001). A plot of thickness by corneal location and time of day exhibited a diurnal pattern, with the peripheral cornea exhibiting progressively greater thickness changes than the central cornea (two-way analysis of variance; P<0.00001). The data significantly correlated across days when all times of day were considered (r = 0.999). However, thickness values obtained at 8:00 AM were significantly different across days (t test; P<0.0002). The subject's data correlated very well (r = 0.9996) with the grouped volunteer data.

CONCLUSIONS

These data show this system to be useful in corneal research and in clinical settings. The data confirm early morning pachymetry to be highly variable. Additionally, the data not only indicate a diurnal variation of corneal hydration over time, but also imply the presence of a diurnal-based hydration gradient across the peripheral cornea, both of which can have significance for PRK, since excimer tissue ablation effectiveness is influenced by tissue hydration.

Unilateral Refractive Keratotomy for Anisometropia

BACKGROUND

In anisometropia, the asymmetry of refractive error produces disparity of image magnification (aniseikonia) that can create visual discomfort, especially when asymmetry is 3.00 diopters or more.

METHODS

A prospective study of 20 eyes of 20 patients between 18 and 61 years of age who underwent unilateral radial and/or transverse keratotomy was conducted; results of at least 12 months follow-up are presented. The efficacy of keratotomy was evaluated by the following criteria: 1) change in spherical and cylindrical refraction, 2) decrease in refraction difference between two eyes of each patient, 3) change in spectacle-corrected visual acuity, and 4) change in binocular vision functions and asthenopic complaints.

RESULTS

Mean decrease in spherical refractive error was 3.66 +/- 1.58 D (range, 1.25 to 7.50 D) and 2.08 +/- 0.81 D (range, 1.00 to 3.50 D) in astigmatic refraction. The mean refraction difference between two eyes was 4.90 +/- 2.20 D preoperatively, and this difference regressed to 1.79 +/- 1.42 D postoperatively. Spectacle-corrected visual acuity increased in seven eyes (35%), remained the same in 12 eyes (60%) and decreased in one eye (5%). All patients reported relief of asthenopic complaints. Fusion amplitudes increased in 12 (60%) patients. Stereoscopic vision improved in five (25%) patients.

CONCLUSION

Monocular refractive keratotomy can significantly decrease anisometropia.

The etiology of refractive changes at high altitude after radial keratotomy. Hypoxia versus hypobaria

OBJECTIVE

Refractive changes at high altitude that occur after radial keratotomy (RK) may be caused by hypoxia or hypobaria.

DESIGN

A prospective study was performed to evaluate the effects of hypoxia on RK and non-RK corneas.

PARTICIPANTS

There were 20 RK and 20 control eyes.

INTERVENTION

These eyes were subjected to ocular surface hypoxia using an air-tight goggle system at sea level for 2 hours.

MAIN OUTCOME MEASURES

Keratometry, cycloplegic refraction, and pachymetry were evaluated using repeated measures analysis of variance.

RESULTS

A significant hyperopic shift (P < 0.0001) and corneal flattening (P < 0.0013) occurred in all subjects with RK compared with those of control subjects. Corneal thickening occurred symmetrically in both groups.

CONCLUSIONS

These results suggest that refractive changes in subjects with RK occur at high altitude as a direct result of corneal hypoxia.

The intrastromal corneal ring segments. Phase II results for the correction of myopia

OBJECTIVE

The purpose of the study was to evaluate the safety and efficacy of the intrastromal corneal ring segments (ICRS) for the correction of myopia.

DESIGN

A 2-year phase II clinical trial of ICRS was initiated in May 1995. The investigational plan specifies that 150 patients with sighted eyes, requiring myopic corrections from -1.00 to -6.00 diopters (D), will each receive ICRS in 1 eye. The patient population will be divided into approximately five patients per ICRS thickness (0.25, 0.30, 0.35, 0.40, and 0.45 mm) per site. Six investigational sites are participating in the trial.

PARTICIPANTS

Fifty-nine men and 43 women requiring myopic corrections were enrolled at four U.S. investigational sites. These 102 patients each received the ICRS product in 1 eye.

INTERVENTION

Correction of myopia.

MAIN OUTCOME MEASURES

Efficacy of ICRS was assessed with respect to the trial endpoints of predictability of refractive effect, uncorrected visual acuity (UCVA), stability of UCVA, maintenance of best spectacle-corrected visual acuity and stability of refractive effect.

RESULTS

As shown by the available month-3 data (99 patients; all device thicknesses), 95 (96%) of 99 patients had a UCVA of 20/40 or better. Ninety-eight (99%) of 99 patients were within 2 lines of their preoperative best spectacle-corrected visual acuity. The average change (with standard error) in cycloplegic refraction (spherical equivalent) achieved by ICRS thickness was -1.27 +/- 0.09 D (0.25 mm), -2.13 +/- 0.16 D (0.30 mm), -2.56 +/- 0.15 D (0.35 mm), -3.77 +/- 0.37 D (0.40 mm) and -4.16 +/- 0.24 D (0.45 mm). Seventy-seven percent (76/99) of the patients were within +/-1.00 D of their intended correction. When the ICRS was removed in two cases, both patients returned to within 0.75 D of their preoperative manifest refraction.

CONCLUSIONS

The ICRS appears to be a viable and effective alternative for the treatment of myopia. Additionally, as indicated by the explant data, the ICRS's refractive effect may be reversible upon removal of the device.

Lack of diurnal variation in vision, refraction, or keratometry after excimer laser photorefractive keratectomy

PURPOSE

To examine whether diurnal variation in visual acuity, spherical equivalent, keratometry, or intraocular pressure occurs in patients who have undergone photorefractive keratectomy.

METHODS

Twenty-nine post-photorefractive keratectomy patients underwent morning and evening measurements of visual acuity, spherical equivalent, keratometry, and intraocular pressure at intervals between 5 and 13 months after photorefractive keratectomy.

RESULTS

There was no statistically significant post-photorefractive keratectomy diurnal variation in visual acuity, spherical equivalent, or keratometry in the group studied. Diurnal variation in post-photorefractive keratectomy intraocular pressure was not significantly different between patients' treated and untreated eyes.

CONCLUSION

Photorefractive keratectomy does not appear to result in diurnal variation in visual acuity, spherical equivalent, or keratometry post-operatively, nor does it seem to effect normal diurnal variation in intraocular pressure.

One-year results of a prospective multicenter study of the Casebeer system of refractive keratotomy. Casebeer Chiron Study Group

PURPOSE

To evaluate the clinical results, predictability, stability, safety, and the patient satisfaction after refractive keratotomy for the correction of myopia and astigmatism using a defined protocol (the Casebeer system).

METHODS

The authors enrolled 324 patients (615 eyes) in a prospective study conducted by 18 surgeons. All procedures were performed using ultrasonic pachymetry with the diamond knife blade set at a length of 100% of the temporal paracentral corneal thickness reading and four to eight centripental (Russian style) incisions with or without fixation of the globe. Straight transverse incisions were done for astigmatism in 222 (36%) eyes. One to eight repeated operations (enhancements) were done on 241 (39%) eyes.

RESULTS

Mean baseline cycloplegic refraction was -3.68 +/- 1.59 diopters (D) (range, -0.88 to -8.25 D). One-year data were available for 546 eyes (89%). At 1 year, mean spherical equivalent cycloplegic refraction was -0.27 +/- 0.78 D (range, -3.13 to +3.00 D). There were 373 (68%) eyes with a refraction of +/- 0.50 D, and 483 eyes (89%) within +/- 1.00 D of emmetropia. Ten eyes (2%) were overcorrected by more than 1.00 D. Mean baseline refractive cylinder was 1.01 +/- 0.75 D (range, 0-5.75 D); at 1 year, the mean cylinder was 0.40 +/- 0.55 D (range, 0-2.50 D). Uncorrected visual acuity was 20/20 or better in 297 (54%) eyes and 20/40 or better in 93%. Six eyes (1%) lost two to three lines of spectacle-corrected visual acuity; the worst visual acuity was 20/30. Of patients responding to a standardized questionnaire, 320 (77%) wore no spectacles for distance or near vision; there was a significant increase in glare and fluctuation of vision from baseline; and 247 (90%) were very satisfied with the outcome.

CONCLUSIONS

Refractive keratotomy using radial incisions with or without transverse incisions and following the Casebeer system effectively reduces and often eliminates myopia and astigmatism with a high degree of safety. Enhancement surgery was required in 39% of eyes. Glare and fluctuation of vision increased postoperatively but were rated mild, and patient satisfaction was high.

Refractive changes during 72-hour exposure to high altitude after refractive surgery

PURPOSE

The authors prospectively analyzed refractive and pachymetric parameters during exposure to high altitude after radial keratotomy (RK) and photorefractive keratectomy (PRK).

METHODS

The authors measured manifest and cycloplegic refraction, keratometry, computed video keratography, and central and peripheral pachymetry in six subjects who have undergone RK (11 eyes), six who have undergone PRK (12 eyes), and nine with myopia (17 eyes) at sea level and on three consecutive days at 14,100 feet. All measurements were repeated 1 week after subjects returned to sea level.

RESULTS

Subjects who have undergone RK demonstrated a significant and progressive increase in spherical equivalence (+0.30 +/- 0.50 diopters on day 1 and +1.52 +/- 1.01 diopters on day 3; P < 0.001) and a decrease in keratometry values during exposure to altitude when compared with control subjects with myopia. Healthy subjects and those who have had PRK demonstrated no significant change in refractive error. Pachymetry measurements demonstrated significant peripheral corneal thickening in all three groups (RK, P < 0.004; PRK, P < 0.007; control subjects, P = 0.0006) by day 3 at high altitude. Refraction, keratometry, and pachymetry returned to baseline (P = 1.000) after return to sea level.

CONCLUSIONS

Seventy-two-hour exposure to high altitude in subjects who have had RK induces a significant, progressive, and reversible hyperopic shift in refraction with corresponding video keratographic and keratometric changes. The authors hypothesize that the high-altitude hypoxic environment causes increased corneal hydration in the area of the RK incisions, which may lead to central corneal flattening and a hyperopic shift in refractive error. Subjects who have had PRK and those with myopia are not susceptible to this refractive shift. The authors' RK data suggest that the time since surgery and the amount of surgery are related to the degree of hyperopic shift during altitude exposure.

Contact lens fitting after photorefractive keratectomy

AIMS/BACKGROUND

This study evaluated contact lens fitting and the longer term response of the photorefractive keratectomy (PRK) cornea to lens wear. In PRK for myopia problems such as regression, anterior stromal haze, irregular astigmatism, halo aberration, and anisometropia have been reported. Certain patients therefore require contact lens correction to obtain best corrected visual acuity (BCVA).

METHOD

From an original cohort of 80 patients, 15 were dissatisfied with their visual outcome 6 months after PRK. Ten of these were fitted with lenses and monitored regularly.

RESULTS

The best fit rigid gas permeable lens of diameter 9.20-10.00 mm was generally 0.10 mm steeper than mean keratometry readings. Because of lid discomfort five patients were refitted with daily wear soft lenses. All 10 achieved satisfactory lens wear of 10 hours per day. Central corneal steepening of 0.75 D (0.15 mm) occurred in one patient. Two patients had slight central corneal flattening. Three patients discontinued lens wear as they found lens care a nuisance. Four finally opted for retreatment by PRK.

CONCLUSIONS

In most cases, contact lenses gave good visual acuity and, in cases of mild irregular astigmatism, a significant improvement over spectacle BCVA. No significant adverse reaction to contact lens wear was found. Although ocular tolerance of lenses was satisfactory, several patients discontinued lens wear or sought improved unaided vision.

Transient Central Corneal Steepening After Radial Keratotomy

Three case studies are presented illustrating topographic transient central steep island following radial keratotomy. Three stages are apparent: first, a central corneal steepening; next, an overcorrection with exaggerated central flattening; and, finally, the final refractive correction. The steepening is probably caused by temporary midperipheral swelling of the cornea.

Mechanical Stability of the Cornea After Radial Keratotomy and Photorefractive Keratectomy

BACKGROUND

Corneal refractive surgical procedures alter the shape and structure of the tissue, possibly compromising its mechanical stability.

METHODS

One or both eyes of 87 subjects were studied: 26 of these 87 had been treated for myopia by excimer laser ablation and 36 by radial keratotomy; 25 without previous corneal surgery functioned as controls. Corneal topography was evaluated by TMS-1 videophotokeratography before and after 180 degrees tilting of the patient, and the pressure-induced ring-wise changes in spherical equivalent power (axial power) were calculated. Changes in corneal shape also were evaluated by computing the instantaneous radius of curvature. The intraocular pressure was measured before and after tilting by a hand-held applanation tonometer.

RESULTS

The mean intraocular pressure increased from 13.9 +/- 2.3 mm Hg before tilting to 30.0 +/- 3.8 mm Hg during tilting. In the control eyes, the mean power of the central cornea during tilting decreased 0.187 +/- 0.045 diopters (D) (p < .05); in the excimer-laser-ablated eyes, 0.038 +/- 0.056 D (not statistically significant); and in those treated with radial keratotomy, 0.523 +/- 0.054 D (p < .01). After radial keratotomy, the cornea steepened outside the clear zone in response to pressure loading, whereas it did not change significantly in the laser-ablated or control eyes.

CONCLUSIONS

Pressure-induced deformation of normal and excimer laser-ablated human cornea is small, whereas radially incised corneas have significantly decreased mechanical stability.

Morning-to-evening change in refraction, corneal curvature, and visual acuity 11 years after radial keratotomy in the prospective evaluation of radial keratotomy study. The PERK Study Group

PURPOSE

Previous reports demonstrate morning-to-evening changes in ophthalmic measurements at 3 months, 1 year, and 4 years after radial keratotomy. The authors determine whether diurnal change in refractive error persists 11 years after radial keratotomy surgery in the Prospective Evaluation of Radial Keratotomy (PERK) study.

METHODS

Seventy-one patients were examined in the morning and evening a mean of 11.1 +/- 0.6 years (range, 10-12.7 years) after undergoing radial keratotomy under a standardized protocol using a diamond blade.

RESULTS

Between the morning and evening examinations, the mean change in the spherical equivalent of refraction was a 0.31 +/- 0.58-diopter (D) increase in minus power in first eyes. Thirty-six (51%) eyes had an increase in minus power of the manifest refraction of 0.50 to 1.62 D; 22 (31%) had a change in refractive cylinder power of 0.50 to 1.25 D; 9 (13%) had a decrease in uncorrected visual acuity of two to seven Snellen lines; and 25 (35%) showed central corneal steepening measured by keratometry of 0.50 to 1.94 D. Two (3%) eyes lost two lines of spectacle-corrected visual acuity, whereas one (1%) eye gained two lines. In patients whose both eyes underwent surgery, a high degree of symmetry was observed in morning-to-evening refractive change.

CONCLUSION

In some patients after radial keratotomy, morning-to-evening change of refraction and visual acuity persists for at least 11 years, although in most patients the magnitude of this change is small. Thus, diurnal fluctuation may be a permanent sequela of radial keratotomy in some individuals.

Efficacy and safety of excimer laser photorefractive keratectomy and radial keratotomy for bilateral myopia

PURPOSE

To compare the safety and efficacy of radial keratotomy (RK) and photorefractive keratectomy (PRK) to correct myopia.

METHODS

In this randomized, prospective, parallel-group study, 33 patients with bilateral myopia of 1.00 to 5.00 diopters (D) had PRK in one eye and RK in the other. The order of surgeries and treatment assignments were randomized, and the bilateral surgeries were within 1 week for each patient. Data were collected using standardized procedures. Clinical measurements and satisfaction surveys were taken in masked fashion.

RESULTS

Eyes that had PRK had statistically significantly more residual myopia than RK-treated eyes at 3, 6, and 12 months postoperatively. This result was attributed to the use of an older excimer laser PRK algorithm that was used at the initiation of the study. No eye that had PRK was overcorrected by 0.50 D or more at 1 year postoperatively, while seven eyes that had RK were overcorrected by at least 0.50 D and six were overcorrected by 1.00 D. Eyes that had PRK had a statistically significant mean shift in the myopic direction between 6 and 12 months postoperatively; two RK eyes had hyperopic shifts of 1.00 D. Three RK eyes and two PRK eyes failed to achieve an uncorrected visual acuity of 20/40 or better by 12 months postoperatively. No eye lost any best corrected visual acuity.

CONCLUSION

The two procedures were comparably safe and effective in treating mild to moderate myopia under this protocol. Eyes that had PRK were somewhat more myopic at 1 year after surgery, attributable to the older PRK ablation algorithm. Adoption of newer (current) laser algorithms has improved the predictability of PRK. There was also evidence of reduced variability of outcome in the PRK group. The PRK eyes did not exhibit hyperopic shifts during the 1 year follow-up.

Refractive changes at extreme altitude after radial keratotomy

PURPOSE

We studied the effects of altitude on four corneas that had undergone radial keratotomy and four normal corneas exposed to increasing elevation during a high-altitude excursion.

METHODS

We measured visual acuity, cycloplegic refraction, keratometry, and intraocular pressure at sea level and after 24-hour exposure to 12,000 and 17,000 ft.

RESULTS

We observed a significant increase in spherical equivalence (hyperopic shift) in radial keratotomy eyes exposed to altitude as compared to controls (P < .0001). The average change in spherical equivalent cycloplegic refraction from sea level to 12,000 ft was 1.03 +/- 0.16 diopters and from sea level to 17,000 ft was 1.94 +/- 0.26 diopters. We also observed a significant decrease in keratometry values at altitude as compared with control corneas (P < .0001). The average change in keratometry from sea level to 12,000 ft was 0.59 +/- 0.19 diopter and from sea level to 17,000 ft was 1.75 +/- 0.27 diopters.

CONCLUSIONS

Although the specific origin of these changes is open to question, we hypothesize that hypoxic corneal expansion in the area of the radial keratotomy incisions may lead to central corneal flattening and a hyperopic shift in refractive error. The cornea that has undergone radial keratotomy appears to adjust constantly to changing environmental oxygen concentration, producing a new refractive error over a period of 24 hours or more. Additional study is required to identify with certainty the specific origin of the hyperopic shift at high altitude.

Dynamic shifts in corneal topography after radial and transverse keratotomy

PURPOSE

The authors aimed to quantitate the dynamic patterns of change in corneal topography after multistaged radial and transverse keratotomy using digitized video-keratography.

METHODS

Single and paired radial and transverse keratotomies, with videokeratoscopy between each stage and at the end of the procedure, were performed on fresh animal cadaver eyes using an artificial orbit system.

RESULTS

All incisions led to central flattening. A single radial keratotomy caused flattening adjacent to the incision, and steepening 180 degrees away. A paired radial keratotomy caused increased flattening in the meridian of the incisions, and less flattening 90 degrees away. A single transverse incision caused steepening adjacent to the incision and diffuse flattening elsewhere. A paired transverse incision caused flattening near the optical center along the meridian bisecting the incisions and steepening 90 degrees away.

CONCLUSION

The authors have demonstrated that computerized videokeratography can be used successfully to systematically quantitate dioptric shifts in multiple hemimeridians and measurement zone diameters after refractive surgery.

The Casebeer system for predictable keratorefractive surgery. One-year evaluation of 205 consecutive eyes

PURPOSE

This study documents the results of current radial keratotomy (RK) surgical technology, using the Casebeer keratorefractive system. These results are contrasted to those of the Prospective Evaluation of Radial Keratotomy (PERK) keratorefractive system, developed approximately 12 years ago.

METHODS

Two hundred five consecutive surgical procedures were examined, which was the first year of experience with RK for one of the authors (TPW). All procedures fit within the Casebeer nomograms. Enhancement procedures were performed following the Casebeer system nomograms.

RESULTS

Follow-up for 100% of patients was achieved. Postoperative cycloplegic refractions yielded an average of +0.27 +/- 0.58 diopters (D) of residual refractive correction (range, -0.88 to +2.50 D). One year postoperatively, 20/25 or better uncorrected visual acuity was achieved in 86% of patients and 20/40 or better uncorrected visual acuity was achieved in 99% of patients. Bothersome but not incapacitating side effects, such as glare, starbursting, and fluctuating vision, have been commonly observed with RK.

CONCLUSION

The Casebeer system for keratorefractive surgery, which is easy to learn, can yield an extremely accurate surgical result. The major reason for increased accuracy compared with the PERK system is the surgeon's ability to titrate the primary surgical procedure with enhancement operations. Although RK is by no means a perfect surgical technique, side effects tend to be relatively minimal, and patient satisfaction tends to be extremely high.

Keratoreformation by contact lenses after radial keratotomy

Since the number of patients undergoing radial keratotomy has increased, more have required contact lens fitting to correct residual ametropia. A number of practitioners suggest that the postoperative changes stabilize after 12 months, so contact lens fitting on the unusual resultant corneal topography can begin. This paper discusses corneal and refractive changes that are revealed even when correctly fitting lenses are worn 1-5 years postoperatively. These changes indicate that lens wear may influence corneal topography and refraction even several years after radial keratotomy.

Stability of refraction during four years after radial keratotomy in the prospective evaluation of radial keratotomy study

The Prospective Evaluation of Radial Keratotomy Study is a nine-center clinical trial of a standardized technique of radial keratotomy in 435 patients who had simple myopia with a preoperative refraction between -2.00 and -8.00 diopters. We studied the stability of the refractive error during four years after surgery for each of 341 eyes first operated on that had a single surgical procedure. Between baseline and two weeks after surgery, all eyes became less myopic; between two weeks and three months, 161 eyes (59%) lost 1.00 D or more of the initial effect; and between three and six months, 266 eyes (95%) had a stable refraction with less than 1.00 D change. The change from six months to four years was less than 1.00 D for 246 eyes (72%). There was 1.00 D or more decrease in surgical effect (increased minus power) for 13 eyes (4%), and 1.00 D or more increase in surgical effect (decreased minus power) for 82 eyes (24%). Eyes with larger amounts of preoperative myopia and smaller diameter of the clear zone were more likely to have an increasing effect of the surgery. The duration of this continued increasing effect of the surgery is unknown.

Effect of corneal hydration and intraocular pressure on keratometric power after experimental radial keratotomy

Persistent diurnal fluctuations in vision are common after radial keratotomy (RK), associated with a myopic change in refraction and keratometric power as the day progresses. A possible relation between keratometric power and either intraocular pressure (IOP) or corneal hydration was investigated in a cadaver eye model. First, keratometric power was measured before and after RK while IOP was varied from less than 0.5 to 20 mmHg. A nonlinear relation was found; in particular, changes in IOP in the physiologic range had no effect on keratometric power after RK. In a second set of experiments, keratometric power was measured after RK as the dehydrated corneas were gradually hydrated with balanced salt solution. After RK, keratometric power decreased markedly as corneal hydration increased (0.33 diopters [D] per 10-microns increase in thickness). The keratometric power of control corneas was not affected by changes in IOP or hydration. The author concludes that diurnal fluctuations in refraction after RK are probably caused by diurnal fluctuations in corneal hydration rather than changes in IOP.

Corrective measures for myopia

Many myopic people, expressing dissatisfaction with traditional methods of optical correction, are interested in a permanent correction of their refractive error which would alleviate dependence on corrective lenses. Although much effort has been put forth in the last century, there is still no method of correcting myopia which is broadly acceptable as safe and effective. The nonsurgical procedures of orthokeratology and the topical use of cycloplegics have not been well proven. Surgical measures are the current vectors of hope. Surgical procedures on parts of the eye other than the cornea have proven to be difficult. Surgery which alters the refractive power of the cornea (refractive keratoplasty) has been used frequently in the past decade. These procedures include keratomileusis, epikeratophakia and radial keratotomy. The latter is currently the most often performed method for the correction of myopia. This paper critiques the major methods, explains their historical development and basic procedures, lists major published studies and discusses their problems and promise for their future.

Radial keratotomy: 500 consecutive cases

A report on 500 consecutive eyes having radial keratotomy for myopia and myopic astigmatism is presented. Surgery was on an out-patient basis under local anaesthetic, with a follow-up of 99.2% of cases, 91.8% of the 294 patients elected to have radial keratotomy on the fellow eye. The surgical protocol was designed to minimise side effects and complications rather than maximise the reduction in myopia. 6/12 unaided vision or better was achieved by 99% of cases in the low myopia group, 91% in the middle and 41% in the high myopia group. Persistent hypermetropia of +1.00D or greater occurred in only 0.4% of cases and secondary astigmatism of 1.00D or greater in 1% of cases. Corneal perforations were minimised by single-pass incisions, but this was at the cost of lesser myopic corrections in the higher myopic group. Centering on the visual axis rather than the centre of the pupil minimised glare sensitivity. No patient developed potentially blinding complications.

The effect of increased intraocular pressure on visual acuity and corneal curvature after radial keratotomy

To detect the effect of increased intraocular pressure on visual acuity and corneal curvature after radial keratotomy, we measured these variables in the sitting and inverted positions in 18 patients who underwent radial keratotomy (Group 1) and compared their results with those from the unoperated on eyes of seven patients (Group 2). We also compared the results before and after inversion within each group. Intraocular pressure increased to approximately two times normal in each group. Significant improvement in visual acuity and reduction in central keratometry were noted only in Group 1. By multiple regression analysis, visual improvement correlated with the number of incisions but not the time since surgery. Our study provides evidence that increased intraocular pressure may account for transient changes in vision and corneal curvature after radial keratotomy.

Corneal topography and fluctuating visual acuity after radial keratotomy

A high-resolution photokeratoscope using computer graphics to model corneal topography was used on patients who had undergone radial keratotomy. After radial keratotomy, central optical zones are created that can be characterized as round, oval or band-like, or dumbbell-shaped or split. The dumbbell form of optical zone was associated with larger amounts of refractive and keratometric astigmatism than the round or band-like zones. The authors correlated the shape of the optical zone with the presence or absence of diurnal variation (fluctuation) in visual acuity. Of the 26 eyes studied, 11 experienced fluctuation and 15 did not. Of those 11 eyes with fluctuating visual acuity, 10 (91%) had dumbbell-shaped or split optical zones and 1 (9%) had a round optical zone. Of the 15 eyes without fluctuation, 12 (80%) had round optical zones and 3 (20%) had band-like zones. The presence of a split or dumbbell-shaped optical zone after radial keratotomy indicates that the patient is likely to experience diurnal fluctuation of visual acuity.