Three-year results of the Prospective Evaluation of Radial Keratotomy (PERK) Study

Surgical options and clinical outcomes for high myopia

PURPOSE OF REVIEW

Higher degrees of myopia are currently being treated with refractive surgery. However, there is limited characterization and outcomes data for this cohort. This article aims to review the literature on highly myopic patients who had refractive surgery and present a retrospective analysis of 149 patients (270 eyes) with high to extreme myopia (≤-5.0D SE) who underwent refractive surgery [laser-assisted subepithelial keratomileusis (LASIK), photorefractive keratectomy (PRK), or implantable collamer lense (ICL)] at a single practice.

RECENT FINDINGS

There is substantial literature on the efficacy of LASIK, PRK, and phakic intraocular lenses for refractive error correction, but a dearth of studies on patients with high to extreme myopia undergoing different types of refractive surgery. Our study reveals that this cohort of patients has excellent outcomes with minimal complications.

SUMMARY

Our study reveals that the average preoperative myopia was highest in ICL patients (-10.03D), followed by PRK (-7.21D), and LASIK (-7.04D) patients. Not surprisingly, eyes with high myopia and thin corneas were offered and elected ICLs for their procedure. Highly myopic patients achieved outcomes consistent with data reported in the literature- average postoperative uncorrected visual acuity was 20/20 for LASIK and ICL eyes and 20/25 for PRK eyes.

Accuracy of Astigmatism Correction with Toric Intraocular Lens Implantation in Eyes with Prior Radial Keratotomy

PURPOSE

To evaluate refractive outcomes of toric intraocular lens (IOL) implantation in eyes with previous radial keratotomy (RK).

SETTING

Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA.

DESIGN

Retrospective case series.

METHODS

Consecutive cases with previous RK and had undergone cataract surgery with Toric IOL implantation and met these criteria were retrospectively reviewed: (1) regular bowtie corneal astigmatism within the central 3.0-mm zone, (2) difference in corneal regular astigmatism magnitude between the IOL Master and Lenstar of ≤ 0.75 D, and (3) difference in the regular astigmatism meridians from the 2 biometers of ≤ 15 degrees, and (3) available postoperative manifest refraction at ≥ 8 weeks with corrected distance visual acuity of 20/30 or better. Vector analysis was used to assess the preoperative corneal and postoperative refractive astigmatism.

RESULTS

In 40 eyes of 31 patients with previous RK, preoperatively the mean magnitude of corneal regular astigmatism was 2.10 ± 0.98 diopters (D), 1 (3%) and 2 (10%) eyes had anterior corneal regular astigmatism ≤0.5 D and ≤1.0 D respectively, and the centroid value was 1.14 D @ 179° ± 2.05D. Postoperatively, the mean magnitude of refractive regular astigmatism was 0.46 ± 0.44D (D), 29 (73%) and 35 (88%) of eyes had refractive regular astigmatism ≤0.5 D and ≤1.0 D respectively, (P<0.05), and the centroid value was 0.12 D @ 173° ± 0.63 D (P<0.05).

CONCLUSIONS

Toric IOLs can be used successfully to treat corneal regular astigmatism in eyes with previous RK.

A Review of Structural and Biomechanical Changes in the Cornea in Aging, Disease, and Photochemical Crosslinking

The study of corneal biomechanics is motivated by the tight relationship between biomechanical properties and visual function within the ocular system. For instance, variation in collagen fibril alignment and non-enzymatic crosslinks rank high among structural factors which give rise to the cornea's particular shape and ability to properly focus light. Gradation in these and other factors engender biomechanical changes which can be quantified by a wide variety of techniques. This review summarizes what is known about both the changes in corneal structure and associated changes in corneal biomechanical properties in aging, keratoconic, and photochemically crosslinked corneas. In addition, methods for measuring corneal biomechanics are discussed and the topics are related to both clinical studies and biomechanical modeling simulations.

Long-Term Outcomes of Radial Keratotomy, Laser In Situ Keratomileusis, and Astigmatic Keratotomy Performed Consecutively over a Period of 21 Years

Purpose. To describe a case of 3 refractive procedures performed in one eye over 2 decades. Methods. Case report. Results. A 41-year-old patient presented for refractive surgery evaluation. His ocular history includes bilateral radial keratotomy performed 21 years ago for moderate myopia: spherical equivalence of −4.25 D bilaterally. Postoperative uncorrected visual acuity (UCVA) was 20/30; however, over time he developed a hyperopic shift and UCVA decreased to 20/40 in the right eye. Thus, laser-assisted in situ keratomileusis (LASIK) was performed at an outside institution 6.5 years later, and the patient had initial improvement of UCVA to 20/25. Due to a change in refractive error, the patient underwent uneventful astigmatic keratotomy 13 years after LASIK in the right eye, and 1.5 years after surgery best-corrected visual acuity was 20/25 with manifest refraction of −1.00 + 5.50 × 134°.  Conclusion. We report the outcomes and natural refractive progression in a patient who underwent three corneal refractive procedures over two decades. This case underlines the difficulties of long-term management of post-RK hyperopia and astigmatism.

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.

Familial aggregation of hyperopia in an elderly population of siblings in Salisbury, Maryland

PURPOSE

To determine whether hyperopia aggregates in families in an older mixed-race population.

DESIGN

Cross-sectional familial aggregation study using sibships.

METHODS

We recruited 759 subjects (mean age, 73.4 years) in 241 families through the population-based Salisbury Eye Evaluation study. Subjects underwent noncycloplegic refraction if best-corrected visual acuity (BCVA) was <or=20/40, had lensometry to measure their currently worn spectacles if BCVA was >20/40 with spectacles, or were considered to be plano (refraction of zero) if the BCVA was >20/40 without spectacles. Preoperative refraction from medical records was used for bilaterally pseudophakic subjects.

RESULTS

Utilizing hyperopia cutoffs from 1.00 to 2.50 diopters, age-, race-, and gender-adjusted odds ratios for hyperopia with an affected sibling ranged from 2.72 (95% confidence interval [CI], 1.84-4.01) to 4.87 (95% CI, 2.54-9.30). The odds of hyperopia increased with age until 75 years, after which they remained relatively constant. Black men were significantly less likely to be hyperopic than white men, white women, or black women.

CONCLUSIONS

Hyperopia appears to be under strong genetic control in this older population.

Night vision disturbances after corneal refractive surgery

A certain percentage of patients complain of "glare" at night after undergoing a refractive surgical procedure. When patients speak of glare they are, technically, describing a decrease in quality of vision secondary to glare disability, decreased contrast sensitivity, and image degradations, or more succinctly, "night vision disturbances." The definitions, differences, and methods of measurement of such vision disturbances after refractive surgery are described in our article. In most cases of corneal refractive surgery, there is a significant increase in vision disturbances immediately following the procedure. The majority of patients improve between 6 months to 1 year post-surgery. The relation between pupil size and the optical clear zone are most important in minimizing these disturbances in RK. In PRK and LASIK, pupil size and the ablation diameter size and location are the major factors involved. Treatment options for disabling glare are also discussed. With the exponential increase of patients having refractive surgery, the increase of patients complaining of scotopic or mesopic vision disturbances may become a major public health issue in the near future. Currently, however, there are no gold-standard clinical tests available to measure glare disability, contrast sensitivity, or image degradations. Standardization is essential for objective measurement and follow-up to further our understanding of the effects of these surgeries on the optical system and thus, hopefully, allow for modification of our techniques to decrease or eliminate post-refractive vision disturbances.

Simulation of air-bag impact on post-radial keratotomy eye using finite element analysis

PURPOSE

To determine the physical and mechanical conditions of an impacting air bag that causes corneal rupture in a post-radial keratotomy (RK) eye using a simulation model of the human eye.

SETTING

Numerical simulation study on a computer.

METHODS

The simulations were performed by a computer using the finite element analysis program PAM-CRASH (Nihon ESI). The air bag was set to impact the surface of a post-RK eye with 4, 6, or 8 corneal incisions at various velocities. Strain on the corneal tissue including scarred incisions exceeding 9.0% was assumed to indicate the possibility of corneal rupture.

RESULTS

At a medium velocity of 30 m/s, corneal rupture was likely to occur. At an air-bag impact velocity of 40 m/s, 3 of 4, 5 of 6, and 8 of 8 incisions were likely to rupture in the case of 4-, 6-, and 8-incision procedures, respectively, leading to likely globe rupture in all situations. Lacerations extended beyond the incisions and involved the intact cornea at a velocity of 40 m/s. If the corneal tissue strength reduction was increased to 90%, most incisions were likely to rupture at impact velocities greater than 35 m/s in all incision procedures.

CONCLUSIONS

The results could partly reflect a reported case of globe rupture after RK and suggest that severe ocular trauma can be caused in the post-RK eye by air bags at ordinary impact velocities.

The cornea in young myopic adults

AIMS

To further understand the effect of refractive error on the corneal dimensions and function.

METHODS

Corneal curvature, corneal thickness, and axial length measurements were performed, as well as specular microscopy and fluorophotometry, on patients with various refractive statuses. 216 subjects, mean age 22.2 (SD 4.2) years, were examined. Patients with previous contact lens wear history, external eye diseases, as well as previous ocular surgeries, were excluded.

RESULTS

The corneas were flatter in eyes with longer axial length (r = -0.22, p = 0.003). Eyes with more myopic spherical equivalent had longer axial length (r = -0.90, p <0.001) as well as less corneal endothelial density (r = 0.20, p = 0.037). Corneal endothelial density decreased in eyes with longer axial length (r = 0.24, p = 0.019); however, it correlated neither with corneal thickness (r = -0.06, p = 0.59) nor with corneal curvature (r = -0.07, p = 0.52). The corneas had a mean corneal thickness of 533 (SD 29) microm and were thinner in more myopic eyes (r = 0.16, p = 0.021). The corneas tended to be thinner in eyes with longer axial length. However, the correlation did not reach statistical significance (r = -0.11, p = 0.14). Besides, there was no significant correlation between the corneal thickness and the corneal curvature (r = -0.13, p = 0.093) and the endothelial permeability (r = 0.042, p = 0.69). The corneas with higher endothelial density had larger corneal transfer coefficient (r = 0.26, p = 0.024) and higher permeability to fluorescein molecules (r = 0.28, p = 0.014). Nevertheless, the corneal endothelial permeability did not correlate significantly with either the axial length (r = -0.18, p = 0.11) or the degree of myopia (r = 0.12, p = 0.26).

CONCLUSION

Changes in the anterior segments as the eyeball elongates in myopia progression included flatter corneal curvature, decreased corneal thickness, as well as decreased endothelial density. These factors should be considered in refractive surgery.

Making sense of refractive surgery in 2001: why, when, for whom, and by whom?

Surgical alteration of the focusing or refractive properties of the eye has been performed on millions of patients. An array of procedures to correct myopia, hyperopia, astigmatism, and presbyopia have been introduced over the past 25 years with varying degrees of success. Improved technology has increased patient and physician satisfaction and enthusiasm. Currently available surgical procedures can be categorized as incisional, surface-altering, lamellar, and intraocular. The choice of procedure depends on individual patient indications and contraindications based on results of ocular examinations, eg, corneal pachymetry to measure corneal thickness, keratometry to measure the corneal curvature, basal tear secretory rate, and dark-adapted pupil size. The postoperative uncorrected visual acuity depends, in large part, on the quality of the preoperative evaluation and refraction. Before scheduling a patient for surgery, the ophthalmologist must ensure that the patient understands the potential risks of the procedure and has realistic expectations for the postoperative level and quality of uncorrected visual acuity. Postoperative complications include corneal flap displacement, undercorrection and overcorrection, and epithelial ingrowth under the corneal flap and inflammatory keratitis. Postoperative dry eye, infection, and inflammation are usually treated medically. Ongoing technological innovations to customize the surgical approach to an individual patient's eye continue to improve outcomes.

Correlation Between Refractive and Corneal Topographic Changes After Photorefractive Keratectomy for Myopia

PURPOSE

To compare videokeratographic and refractive data obtained before and after photorefractive keratectomy (PRK) for myopia.

METHODS

Seventy-four eyes underwent PRK for myopia ranging from -2.50 to -17.00 D (mean, -7.76 +/- 3.17 D). All patients had videokeratography with the EyeSys instrument before, and 1 and 6 months after PRK, and the changes in three corneal power measurements (center of the ablation, apex, and effective refractive power) were compared with refractive changes.

RESULTS

Changes obtained in the three corneal power measurements at 1 and 6 months were well correlated with manifest refraction (Pearson's coefficient ranged from 0.71 to 0.84).

CONCLUSION

Power measurements obtained with corneal topography, as described above, are a reliable and objective method for the evaluation and follow-up of PRK, provided addition of an approximate 25% correcting factor.

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.

Improvement of visual function with glare testing after photorefractive keratectomy and radial keratotomy

PURPOSE

To evaluate the effect of a glare source on visual function in patients after photorefractive keratectomy and radial keratotomy.

METHODS

Thirteen patients (22 eyes) who underwent photorefractive keratectomy and 20 patients (40 eyes) who underwent radial keratotomy were evaluated in this cross-sectional study. LogMAR visual acuity and contrast sensitivity were measured. Pupils were measured with the Rosenbaum card. A halogen/tungsten glare source approximated the luminance of headlights of an oncoming car at 100 feet.

RESULTS

In the photorefractive keratectomy and radial keratotomy groups, pupils were significantly smaller (P<.01) and the pupillary clearance of the ablation zone in photorefractive keratectomy and the clear zone in radial keratotomy were significantly larger under the glare condition (P<.01). In the photorefractive keratectomy group, visual acuity and contrast sensitivity under the glare condition were significantly higher than in the no-glare condition (P = .02). In the radial keratotomy group, contrast sensitivity under the glare condition was significantly higher than under the no-glare condition (P = .001 to .003).

CONCLUSIONS

After photorefractive keratectomy or radial keratotomy, the traditional glare source constricted the pupil and partially masked the optical aberrations, which resulted in an improvement in visual function. A "pupil-sparing" aberration test is needed for evaluation of visual function after refractive surgery.

Dehiscence of a radial keratotomy incision during clear corneal cataract surgery

We report a case of dehiscence of a radial keratotomy (RK) incision caused by clear corneal cataract surgery. The patient had eight-incision RK in both eyes 9 months previously with enhancement surgery in the left eye 1 month later. Cataract surgery through a clear corneal incision was performed in the right eye and 1 month later, in the left. Surgery in the right eye was uneventful. However, during surgery in the left eye, dehiscence of one radial incision occurred. The wound dehiscence was closed with interrupted sutures, and the patient achieved 20/20, uncorrected visual acuity 1 week after surgery.

Photorefractive keratectomy. A 6-year follow-up study

OBJECTIVE

This study aimed to assess the long-term stability and efficacy of excimer laser photorefractive keratectomy.

DESIGN

Patients who participated in the first United Kingdom photorefractive keratectomy clinical trial were asked to attend a 6-year follow-up assessment.

PARTICIPANTS

Eighty-three patients (68%) of the original cohort of 120 participants were observed for 6 years. A Summit Technology UV200 excimer laser with a 4-mm ablation zone had been used with patients allocated to one of six groups according to their preoperative refraction. Each group received one of the following spherical corrections: -2, -3, -4, -5, -6, or -7 diopters (D). Within each group, all patients received an identical treatment, and thus emmetropia was not the goal in all patients.

INTERVENTION

The induced refractive change, objective corneal haze, glare, and halo measurements, together with possible late-phase complications, were analyzed.

MAIN OUTCOME MEASURES

All groups achieved a refractive undercorrection, and the magnitude of the undercorrection was related to the size of the attempted correction. The induced refraction stabilized by 6 to 12 months and has been maintained up to the 6-year follow-up stage.

RESULTS

Ninety-one percent of patients who underwent a -2.00-D correction and 76% of patients who received a -3.00-D correction were within +/- 1 D of the intended refraction at 6 years. Fifty-seven percent of the -4.00-D group and 50% of those in the -5.00-D group were within +/- 1 D, and this was reduced further to 43% in the -6.00-D group and 19% in the -7.00-D group. Six patients (7%) had evidence of residual corneal haze, which was visually significant in two patients (3%). Ten patients (12%) had significant night halos due to the small 4-mm ablation zone that was used in this early treatment trial.

CONCLUSIONS

There was no further regression of the refraction after 1 year, and, more important, there was no sign of hyperopic shift or diurnal fluctuation in the patients' refraction. In addition, corneal haze appeared to reduce further with time, with no intraocular or retinal side effects being noted. Night halos remain a significant reported problem in a small number of patients who were treated with the 4-mm ablation zone.

The prediction of surgically induced refractive change from corneal topography

PURPOSE

To develop a method to predict the refractive power of the cornea from corneal topography.

METHODS

We reviewed preoperative and postoperative cycloplegic refraction, keratometry, and corneal topography in 40 eyes of 40 patients who had undergone photorefractive keratectomy, radial keratotomy, myopic keratomileusis in situ, or hyperopic lamellar keratoplasty. For each axial dioptric power map, we calculated the aspheric ellipsoid that best fit that map. Central corneal points were weighted more heavily than peripheral points, based on the Stiles-Crawford effect. The equation of the best-fit ellipsoid yielded the spherical and astigmatic power and axis for each cornea preoperatively and postoperatively.

RESULTS

The preoperative corneal spherical and astigmatic powers measured by the best-fit method were consistent with the spherical and astigmatic powers measured by keratometry and simulated keratometry. The change in corneal spherical power predicted by the best-fit method was significantly (P < .05) more accurate at predicting the change in spherical equivalent refraction than change either in spherical equivalent keratometry or in spherical equivalent simulated keratometry. The prediction of the astigmatic change was less precise than that of the spherical, but the best-fit method was the most accurate.

CONCLUSIONS

The best-fit method is more accurate than simulated keratometry and standard keratometry are in evaluating corneal refractive power after refractive surgery. An improved method of calculating corneal refractive power may facilitate subjective refraction after refractive surgery, improve the accuracy of intraocular lens power calculation for eyes that have had previous refractive surgery, and improve ablation profiles for excimer laser refractive surgery.

Ocular integrity after refractive procedures

PURPOSE

The purpose of the study was to determine the integrity of human eyes after refractive procedures.

METHODS

Whole human globes underwent either radial keratotomy (RK) with eight incisions, automated lamellar keratoplasty (ALK), photorefractive keratectomy (PRK), or excimer laser assisted in situ keratomileusis (LASIK). Eyes then were subjected to quantitatively increasing levels of trauma until rupture occurred.

RESULTS

All eyes operated on required less energy to rupture as compared with that of control eyes. The mean number of trials required for rupture is as follows (energy doubled with each successive trial): normal, 4.29; LASIK, 3.80; ALK, 3.67; PRK, 3.60; and RK, 2.83. The level of energy required to rupture normal, ALK, PRK, and LASIK eyes was not significantly different. All RK eyes ruptured at incisions. Most ALK, PRK, and LASIK eyes ruptured near the flap edge or limbus. Most normal eyes ruptured with both corneal and scleral involvement. Age of tissue donors at the time of death and time elapsed between death and procedure were not significantly different between groups (P = 0.88 and 0.79, respectively).

CONCLUSIONS

The energy required to rupture ALK, PRK, and LASIK eyes is not significantly different from that for normal eyes. The RK eyes ruptured with significantly less energy than did normal eyes. All RK eyes ruptured at incision sites.

Age-related Refractive Shifts in Simple Myopia

BACKGROUND

An understanding of physiologic age-related shifts in myopic refractive errors is important to the refractive surgeon for the interpretation of long-term results, surgical planning, and patient counseling. This study characterizes the refractive stability of adult simple myopia with a retrospective study of 413 eyes.

METHODS

Approximately 74,000 patient records were analyzed to identify 208 adults with -1.00 to -6.00 diopters (D) of myopia who were followed for more than 20 years at the Spokane Eye Clinic. Amounts of myopic shift (increase in myopia) and hyperopic shift (decrease in myopia) were identified and analyzed within the population. The results were compared to long-term studies of radial keratotomy.

RESULTS

The mean changes per patient age decade were: 20s, -0.60 D; 30s, -0.39 D; 40s, -0.29 D; 50s, +0.28 D; 60s, +0.41 D. Reanalyzed Prospective Evaluation of Radial Keratotomy (PERK) study 10-year postoperative data demonstrated progressively increasing hyperopic shifts per decade, at least to age 50.

CONCLUSION

The normal adult population with simple myopia differs from the general population and consists of a population subgroup that is relatively stable and other subgroups that experience significant refractive shift. The hyperopic shift after radial keratotomy appears to be surgically induced and may be larger than previously thought.

Three year results of refractive keratotomy using the Casebeer System

PURPOSE

To analyze the results of one surgeon's first refractive keratotomy surgeries.

SETTING

The Werblin Center, Princeton, West Virginia.

METHODS

The three year results of 241 consecutive surgical procedures (128 patients) using Casebeer nomograms were examined. The average preoperative myopia was -4.07 +/- 1.89 diopters.(D). Two hundred twenty-two eyes were corrected with a goal of emmetropia. Two hundred of 241 eyes (83%) were followed for 3 years; 35 eyes (15%) were followed for fewer than 3 years after the last enhancement procedure, and 6 eyes (2%) were lost to follow-up.

RESULTS

At 3 years postoperatively (range 30 to 44 months), excluding postoperative suture and ALK procedures, mean residual manifest refractive error (spherical equivalent) was -0.04 +/- 0.67 D (-2.25 to + 3.13 D). Mean residual cycloplegic error was + 0.45 +/- 0.76 D (-1.00 to + 4.13 D). Eighty-seven eyes (36%) required between one and six enhancement procedures. One hundred fifteen eyes (52%) had 20/20 or better visual acuity and 214 eyes (96%), 20/40 or better. One hundred fifty-two eyes (84%) were within +/- 1.0 D and 120 eyes (66%) were within +/- 0.5 D. Ten eyes (4%) lost one or more lines of best corrected acuity.

CONCLUSION

Using the Casebeer system for refractive keratotomy, we obtained 20/40 or better uncorrected visual acuity in 96% of eyes with low to moderate levels of myopia. However, a significant number of enhancement procedures, 36% overall, were required to achieve this level of success. Hyperopic shift remains a significant concern following radial keratotomy procedures.

Measurement of Irregular Astigmatism Using Semimeridian Data from Videokeratographs

BACKGROUND

Irregular astigmatism is one of the most troublesome side effects of corneal surgery. We attempted to quantify irregular astigmatism in a simple way, using semimeridian data from videokeratographs of corneas with different amounts of irregular astigmatism.

METHODS

We studied the corneal topography of 30 normal corneas to be used as controls, 30 corneas from patients after radial keratotomy, 30 corneas from patients after nonfreeze myopic keratomileusis, and 30 corneas with clinically apparent keratoconus. We developed two diagnostic formulas, a refractive power symmetry index and an angle symmetry index, using the absolute-scale, color-coded map, and semimeridian data from the EyeSys Corneal Analysis System, and used them to compare the four groups of corneas.

RESULTS

In the corneas with irregular astigmatism, values for the refractive power symmetry index and angle symmetry index were significantly higher than in the normal corneas. The refractive power symmetry index confidence interval set at 95% was 0.58 diopters (D) (range 0.00 D to 0.58 D) in the control group. Using these limits, most values in the radial keratotomy, keratomileusis, and keratoconus groups were abnormal. Spectacle-corrected visual acuity correlated negatively with the refractive power symmetry index (rs = -0.58, p < .001). The refractive power symmetry index sensitivity and specificity were respectively 97% and 66%. Spectacle-corrected visual acuity did not correlate with the angle symmetry index.

CONCLUSIONS

Semimeridian data from videokeratographs can be used to quantify irregular astigmatism.

Collamer intraocular contact lens to correct high myopia

PURPOSE

To determine the feasibility of using posterior chamber intraocular contact lenses to treat myopia.

SETTING

Ambulatory surgery centers in Torino, Ancona, and Ivrea, Italy.

METHODS

The phakic intraocular contact lens is made of a collagen copolymer. We implanted 15 of these lenses in 14 patients with preoperative spherical equivalents ranging from -10.8 to -24.0 diopters (D); average myopia was -15.3 D +/- 3.1 (SD). Average follow-up was 7.0 +/- 1.95 months.

RESULTS

Mean postoperative spherical equivalent was -2.0 +/- 1.6 D. Uncorrected visual acuity improved in 14 eyes. Best spectacle-corrected acuity was maintained or improved in all but one eye. No iritis or cataracts were observed. Six months postoperatively, the mean endothelial cell loss was 4%. A pupillary block requiring a superior peripheral iridectomy occurred in one eye.

CONCLUSIONS

Because of the incomplete follow-up, we cannot draw conclusions about the long-term safety of the implantable contact lens. The intimate contact between the contact lens and the natural lens raises the possibility of cataract formation. However, examination by Scheimpflug photography and ultrasound biomicroscopy showed no progressive lens opacities.

Eye Infections After Refractive Keratotomy

BACKGROUND

Ocular infections are serious and potentially vision-threatening complications of refractive keratotomy. We have performed an integrative review of published literature to address important issues concerning these complications.

METHODS

Articles in MEDLINE and published manuscripts and abstracts reporting previously unpublished cases of infections after refractive keratotomy were systematically identified and reviewed. Our review did not target patients treated with relaxing incisions for postkeratoplasty astigmatism. Pertinent data were abstracted and analyzed.

RESULTS

Forty-three cases (47 episodes: 42 keratitis and 5 endophthalmitis) of infection appeared in 26 published reports from 1975 to 1994. The frequency ranged from 0.25% to 0.70%. In 22 (47%) eyes, infection occurred before 2 weeks. Thirty-five (74%) infections were located in the inferior half of the cornea, and 22 (62%) were located in the inferotemporal quadrant. Thirty-one (66%) infections were bacterial (32% gram-positive, 23% gram-negative, 9% acid fast, 496 unknown), 5% fungal, 6% viral, 19% sterile, and 4% of unknown origin. Spectacle-corrected visual acuity after conservative treatment was 20/40 or better in 70% of eyes. Penetrating keratoplasty was performed in six cases. Potential associations included reoperations in 12 (26%) eyes, postoperative contact lens wear in 7 (15%), and intraoperative perforation in 7 (15%).

CONCLUSIONS

The published literature indicates that infections after refractive keratotomy may compromise visual function. Approximately half of the infections occur in the first 2 weeks. Reoperations, postoperative contact lens wear, and intraoperative perforations may be significant risk factors.

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.

Penetrating keratoplasty after radial keratotomy. A report of six patients

BACKGROUND

For more than 15 years, radial keratotomy has increased in popularity as an option for treating myopia in the United States. During this period of time, the procedure has been modified to improve results and decrease complications. Despite these changes, complications from radial keratotomy continue to occur. The authors report six cases of penetrating keratoplasty performed to correct significant loss of vision resulting from complications of radial keratotomy.

METHODS

The surgical records of one author (WR) were reviewed retrospectively for penetrating keratoplasties performed for complications of radial keratotomy.

RESULTS

Six cases of penetrating keratoplasty performed for complications of radial keratotomy were found. Severe loss of vision was the indication for surgery in each case, and was associated with aggressive and repeated incisional refractive attempts to correct astigmatism, hyperopic overcorrection, residual myopia, or refractive errors associated with keratoconus. Glare associated with subepithelial scarring and irregular astigmatism were the primary findings associated with loss of vision.

CONCLUSIONS

Despite advances in technique and instrumentation, radial keratotomy is limited in the amount of myopia it can correct. The risk for loss of vision increases with increasing number of incisions, intersecting incisions, very small optical zones, and keratoconus.

Diving and hyperbaric ophthalmology

Exposure of the human body to ambient pressures greater than that at sea level may result in various disorders, some of which have ocular manifestations. Additionally, some eye disorders and postoperative states may be adversely affected by the underwater environment or other hyperbaric exposures. The prevalence of recreational, military, and commercial diving, as well as the medical use of hyperbaric oxygen therapy, requires that ophthalmologists be familiar with the effects of the hyperbaric environment on the normal and diseased eye. The ophthalmology and diving medical literatures were surveyed for publications relating to the ophthalmic aspects of diving and hyperbaric exposures. Underwater optics, underwater refractive correction, and ophthalmic aspects of a fitness-to-dive evaluation are summarized. The evaluation and management of ocular manifestations of decompression sickness and arterial gas embolism are reviewed and guidelines for diving after ocular surgery are proposed.

Changing practice patterns in refractive surgery: results of a survey of the American Society of Cataract and Refractive Surgery

A questionnaire on refractive surgical practice was sent to the entire membership of the American Society of Cataract and Refractive Surgery in 1992. One thousand eight hundred and forty-one (1,841) of the 4,950 members returned the survey for a response rate of 37.2%. The questionnaire was designed to be self-administered and elicited information on types of refractive procedures performed in the survey year and the preceding year, as well as the intent to perform refractive procedures in the future. Surgeons who perform radial keratotomy (RK) increased from 22% in 1991 to 30% in 1992; 45% expected to perform RK in 1993-1994. The following categories of information were requested: characteristics of RK patients, techniques used by the surgeon, characteristics of the surgeon's overall practice, type of RK training, surgical outcome, and prevalence of complications. The results of this survey indicate that the use of RK and astigmatic keratotomy (AK), as well as other refractive procedures, is steadily increasing. Radial keratotomy was mainly performed on patients 20 to 49 years of age who had low to moderate myopia. The majority of surgeons used four to eight radials, centrally directed incisions, and single depth settings. Three quarters of the surveyed RK surgeons used the Casebeer nomogram. The survey results indicated that 42% of surgeons performing photorefractive keratectomy (PRK) did not perform RK or other refractive procedures, suggesting that growth in the practice of PRK following FDA approval may come from both current RK surgeons and novice refractive surgeons.

Complications of myopic photorefractive keratectomy with the excimer laser

BACKGROUND

Although many thousands of myopic eyes have been operated on by excimer laser photorefractive keratectomy (PRK), the safety of this procedure is still a concern.

METHODS

The results and complications of PRK have been studied for up to 2 years in a prospective trial including 193 eyes in 146 patients. In addition, specific complications of PRK are described that occurred in patients outside the prospective study.

RESULTS

Two eyes (1.2%) lost two lines of best-spectacle-corrected visual acuity 1 year after surgery, but at 2 years one of these eyes had regained baseline visual acuity. At 1 year, 12 eyes (7.1%) had lost more than two lines of visual acuity under glare conditions. Significant complications such as manifest scarring, overcorrection, undercorrection, and continued regression are dependent on attempted refraction. Eccentric ablations with resultant induced astigmatism are rare and the incidence is dependent on the experience of the surgeon. Progressive hyperopia did not occur.

CONCLUSION

Except in corrections greater than 6 diopters, complications after PRK are rare. Assuming an appropriate patient selection, PRK may be considered a relatively safe procedure compared with other refractive procedures.

Radial keratotomy for intolerable myopia after penetrating keratoplasty

Radial keratotomy was used to treat intolerable myopia in nine patients aged 56 to 86 years who had previously undergone penetrating keratoplasty and intraocular lens placement. The degree of myopia ranged from -5.25 to -9.25 diopters spherical equivalent before radial keratotomy. An eight-cut radial keratotomy with either a 4.0- or 4.50-mm central clear zone was performed on all patients. One year after the radial keratotomy, the spherical equivalent ranged from -1.25 to +1.63 diopters, which rendered all patients spectacle tolerant. Endothelial cell counts done before and one year after radial keratotomy demonstrated no marked loss of endothelial cell density. No complications were seen as a result of the radial keratotomy.

Corneal topography of excimer laser photorefractive keratectomy

The application of the 193 nm excimer laser for keratorefractive surgery promises to deliver a higher degree of precision and predictability than traditional procedures such as radial keratotomy. The development and evaluation of keratorefractive surgery have benefited from the parallel advances made in the field of corneal topography analysis. We used the Computed Anatomy Topography Modeling System (TMS-1) to analyze a Louisiana State University (LSU) Eye Center series of patients who had photorefractive keratectomy for the treatment of myopia with the VISX Twenty/Twenty excimer laser system. The excimer ablations were characterized by a relatively uniform distribution of surface powers within the treated zone. In the few cases that exhibited marked refractive regression, corneal topography analysis showed correlative changes. With topographical analysis, centration of the ablations relative to the center of the pupil could be evaluated. Marked improvement in centration occurred in the patients of LSU Series IIB in which the procedure to locate the point on the cornea directly over the pupil's center during surgery was refined. Corneal topographical analysis provides objective measures of keratorefractive surgical results and is able to measure the precise tissue removal effect of excimer laser ablation without the uncertainties caused by measuring visual acuity alone. Our observations forecast the need for improved aids to center the laser ablations and for the development of a course of treatment to prevent post-ablation stromal remodeling.

Topographical analysis of the centration of excimer laser photorefractive keratectomy

A major advantage of myopic photorefractive keratectomy (PRK) is the precision with which the excimer laser ablates corneal tissue. But like other refractive surgery procedures, PRK must solve the problem of accurately centering the treatment zone. We present our technique for PRK centration with postoperative corneal topographic data on 110 patients from Phase IIB and III of the clinical trials. The distance between the center of the post-PRK flat zone and the corneal vertex was determined by topography in millimeters and meridian degrees. On average, treatment zones were decentered down and right 0.52 mm at 196.74 degrees; 92.73% were centered within 1.00 mm, while 57.27% were within 0.50 mm. The centration data were correlated to postoperative visual acuity as well as treatment zone diameter. Mean uncorrected visual acuity was 20/20 for decentrations up to 1.00 mm but fell to 20/30 for deviations greater than 1.00 mm. Best corrected acuity was also preserved below 1.00 mm but compromised above this level. No difference in decentration was found between 4.5 mm and 5.0 mm ablation zones. Our findings indicate that PRK centration is accurate within 1.0 mm in over 92% of cases and that visual acuity is relatively preserved despite deviations from perfect centration. Further technical improvements will enhance the accuracy of PRK.

Visual results after RK

The series of radial keratotomy (RK) in 79 myope eyes in 60 patients was studied to evaluate improvement of uncorrected visual acuity. The main aim with radial keratotomy was to help patients see better without glasses or contact lenses. Myopia ranged from -1.0 D to -9.0 D. Forty-two eyes (53%) achieved uncorrected visual acuity (VA) of 1.0 or better and 73 eyes (92%) better than 0.5. The follow-up period ranged from 3 months to 3.5 years. Postoperatively the most common complication was undercorrection. The risk for progressive myopia made surgeons cautious not to overcorrect patients and to leave them slightly myopic.

Radial keratotomy: a review of 300 cases

Three hundred consecutive cases of radial keratotomy performed between 1985 and 1990 were reviewed. There were no sight threatening complications of surgery and no patient lost one or more lines of corrected Snellen acuity. Overall 78.7% saw 6/12 or better unaided postoperatively and 51.7% saw 6/6 or better. Refraction showed 61.3% to be within 1 dioptre of emmetropia and 86.7% were within 2 dioptres. Further analysis demonstrated that results of unaided acuity and proximity to emmetropia were much better for low (< -2.87 D) and moderate (-3.0 to -5.87 D) than for high (> -6.0 D) myopes.

Excimer laser photorefractive keratectomy. 18-month follow-up

PURPOSE

This study, comprising 120 patients (follow-up, 12 to 22 months; mean, 18 months), was designed to evaluate the efficacy and safety of excimer laser photo-refractive keratectomy.

METHODS

Ablation zone diameter (4 mm), ablation rate (0.22 microns/pulse), fluence (180 mJ/cm2), and frequency (10 Hz) were kept constant, and all patients used a standard topical corticosteroid regimen.

RESULTS

Overcorrection was followed by regression to a stable refraction by 4 months. At 1 year, 95% and 70%, respectively, of patients undergoing - 2.00 diopters (D) and -3.00 D corrections and 40% and 20% of those undergoing -6.00 D and -7.00 D corrections were within +/- 1.00 D of intended refraction. Anterior stromal "haze," maximal at 6 months and diminishing thereafter, was detected in 110 patients (92%). However, best-corrected Snellen visual acuity was reduced in only 22 (18%). Good correlation existed between haze and regression (r = 0.68). Night "halos," due to the relatively small 4-mm diameter ablation zone, were reported by 94 patients (78%) in the early postoperative period, and, at 1 year, 12 (10%) declined treatment of the other eye because of persistence of this problem.

CONCLUSION

Marked individual variation was found after photorefractive keratectomy. However, in low myopia, predictability is "fair," and the procedure is safe. The authors conclude that excimer laser photorefractive keratectomy holds considerable promise for refractive surgery in the future.

Combined myopia and astigmatism surgery. Review of 350 cases

Between February 1985 and December 1987, 350 eyes had combined radial keratotomy and transverse keratotomy surgery. All procedures were performed by the same surgeon. The number and length of the radial and transverse incisions were varied according to the surgeon's clinical judgment based on his personal experience and the nomograms developed by Thornton. Our results showed that 93% of the eyes had 20/40 or better uncorrected visual acuity at the last follow-up visit. The data indicate that quantifiably predictable results can be achieved with this procedure and that results appear stable up to five years after surgery in 80% of the documented cases. There was a tendency toward increasing effect of the transverse incisions in 20% of cases studied. This seems to correlate well with previous studies measuring long-term results with radial incisions for myopia.

Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study five years after surgery. The Perk Study Group

In the Prospective Evaluation of Radial Keratotomy (PERK) Study, 793 eyes of 435 patients with 2 to 8 diopters (D) of myopia received a standardized surgery consisting of 8 incisions with a diamond-bladed knife set at 100% of the thinnest paracentral ultrasonic corneal thickness measurement and a diameter of the clear zone of 3.0 to 4.5 mm; 97 eyes (12%) received an additional 8 incisions. There were 757 eyes (95%) followed for 3 to 6.3 years. After surgery, uncorrected visual acuity was 20/40 or better in 88% of eyes. The refractive error was within 1 D of emmetropia for 64% of eyes; 19% were myopic and 17% were hyperopic by more than 1 D. Between 6 months and 5 years after surgery, 22% of the eyes had a refractive change of 1 D or more in the hyperopic direction. For 25 eyes (3%) there was a loss of 2 or more lines of best spectacle-corrected visual acuity.