Fitting contact lenses after myopic keratomileusis.

PURPOSE: To evaluate the long-term efficacy and results of contact lens fitting following myopic keratomileusis (MKM). SETTING: Department of Ophthalmology, Manhattan Eye, Ear, and Throat Hospital, and Swinger Vision Center, New York, New York, USA. METHODS: Postoperative fitting of contact lenses was studied as part of a prospective evaluation of myopic keratomileusis. In this series, 27 eyes of 20 patients had residual postoperative refractive errors that were corrected with contact lenses. Patients were fit at a mean of 9.4 months after surgery by the trial-lens method. Preoperative keratometry readings and refractions, as well as postoperative keratometry readings, refractions, and contact lens specifications, were recorded and used for fitting. RESULTS: Twenty-six eyes (96%) were fit successfully: 24 (89%) with rigid gas-permeable lenses and 2 (7%) with daily-wear soft lenses. The mean diameter of the rigid lenses was 10.00 mm (range 9.4 to 11.0 mm) and the mean base curve, 8.52 mm (range 7.9 to 9.2 mm). The 2 soft lenses had base curves of 8.6 and 8.9 mm. The mean lens power was -5.24 diopters (D) (range -0.37 to -14.75 D), which was, on average, 4.06 D more myopic than the postoperative spectacle refraction. Postoperative keratometry provided a good starting point for the trial lens. Lenses were tolerated for up to 16 years. One eye, fit with a soft lens, developed significant myopia during the fifth year. CONCLUSION: After lamellar refractive surgery, the topography of the cornea is significantly altered. Although the postoperative keratometry readings are steeper than the actual curvature, they are reasonably reliable for determining the base curve of the initial trial lens, validating the use of conventional methods of fitting rigid contact lenses in patients who have had MKM.

Reproducibility of videokeratographic digital subtraction maps after excimer laser photorefractive keratectomy.

BACKGROUND: Digital subtraction photokeratography can best identify topographic changes after excimer laser photorefractive keratectomy (PRK). To evaluate the reproducibility of these topographic maps, the authors used a topographic modeling system to generate multiple subtraction maps from different combinations of technically acceptable preoperative and postoperative maps for eyes that underwent PRK. The assigned patterns for each patient then were evaluated for consistency. METHODS: Seven hundred twenty-two individual subtraction maps were generated for 64 eyes that underwent PRK. A mean of 11.3 maps were generated for each eye. The topography of each map was individually classified as normal, central island, peninsula, or asymmetric. All maps within a set (consisting of examinations for 1 patient at a single postoperative interval) then were examined as a unit to determine the overall topographic classification for that set of maps. Each set in which each constituent map had the same topographic assignment as the set was considered "nonvariant," whereas those sets in which one or more individual subtraction maps had different topographic assignments were considered "variant." RESULTS: Of the 64 sets, 33 (52%) were variant and 31 (48%) were nonvariant. CONCLUSIONS: Any one subtraction map produced by the topographic modeling system may not be a reliable indicator of the excimer effect.

Excimer laser photorefractive keratectomy after radial keratotomy.

BACKGROUND: Correction of residual myopia after radial keratotomy may be attempted with repeated keratotomy surgery, but predictability can be less than satisfactory. Excimer laser photorefractive keratectomy (PRK) provides an alternative approach to improving the refractive result in these patients. METHODS: Twenty-five eyes of 20 patients at five clinical locations underwent PRK for residual myopia after radial keratotomy. The number of incisions ranged from 4 to more than 16. Clear zones ranged from 3 mm to 4 mm. Best corrected visual acuity was 20/20 or better in 16 of the 25 eyes, with a range from 20/12 to 20/80. Uncorrected visual acuity was 20/200 or worse in 15 of the 25 eyes, with a range from 20/25 to finger counting. The interval between radial keratotomy and PRK averaged 33.5 months, with a range from 5 to 96 months. Nineteen eyes had 6 months or more of follow up; 15 had 12 months or more. RESULTS: Corneal haze was maximal 1 month after surgery (mean +/- SE, 0.65 +/- 0.09), and declined to 0.35 +/- 0.16 at 12 months. Twelve months after PRK, mean keratometric readings were 40.19 +/- 0.81 diopters (D) and mean spherical equivalent refraction was -1.42 +/- 0.47 D. Nine (60%) of the 15 eyes with 12 months follow up were within 1 D of emmetropia and 12 (80%) were within 2 D. Eight (53%) of the 15 eyes had uncorrected visual acuities of 20/40 or better. Spectacle-corrected visual acuity in the eyes with 12 months follow up improved in 4, did not change in 4, and worsened in 6. CONCLUSIONS: The results of PRK are less predictable in eyes that have previously undergone radial keratotomy, and these eyes respond with more haze after PRK than normal eyes.

Single-grating laser pulse stretcher and compressor.

Stretching and compressing of laser pulses is demonstrated with a single-grating apparatus. A laser pulse of 110 fs is stretched to 250 ps and then recompressed to 115 fs. The apparatus exploits a two-level structure: one level for stretching and the other for compressing. This single-grating configuration shows significant simplification in structure and alignment over existing multiple-grating systems. Such a stretcher-compressor is particularly suitable for use with chirped-pulse amplification in which laser wavelength tuning is desirable. Only one rotational adjustment is rquired to restore the alignment of the entire stretcher and compressor when the laser wavelength is changed.

Histopathology of human keratorefractive lenticules.

Eight human corneal lenticules (three from keratophakia, two from hypermetropic keratomileusis, and three from myopic keratomileusis) were examined by light and electron microscopy. The keratophakic lenticules were removed for optical reasons 3, 3.5, and 6 months after surgery. Microscopically, all displayed hypocellularity, mature collagen fibrils and microfibrils, keratocyte ghosts, and keratocytic debris. The hypermetropic keratomileusis specimens were removed at 13 and 14 months postoperatively, the first because of opacities from enzymatic digestion of the cornea, and the second due to contact lens-induced erosion of Bowman's layer and decreased lacrimal secretion. Ultrastructurally, both lenticules exhibited fractures in Bowman's layer, and the 14-month specimen showed multilayered squamous epithelia. The myopic keratomileusis specimens were removed at 4, 8, and 48 months postoperatively due to opacification of the interface caused by delayed epithelial healing, detergent trauma, and previous epithelization, respectively. Electron microscopy revealed fractures in Bowman's layer, subepithelial fibrocellular growth, sparse keratocyte populations of the anterior stroma, porous collagen bundles, keratocytic debris, and regions of epithelial ingrowth.

Nonfreeze epikeratophakia for the correction of myopia.

We developed a procedure for preparing epikeratophakia tissue lenses for the correction of myopia from unfrozen tissue using a newly developed artificial anterior chamber and the BKS-1000 (Barraquer-Krumeich-Swinger) refractive set. The results of 23 clinical cases involving tissue that was not frozen or lyophilized demonstrate a correlation coefficient of 0.90 in terms of accuracy of correction and good visual acuity results.

Postoperative astigmatism.

With the numerous significant advances in surgical methodology--e.g., microinstrumentation, the operating microscope, the surgical keratometer, and intraocular lenses--that have been developed over the past two decades, both surgeons and patients have become increasingly aware of the final optic result of any surgical intervention. This is especially so since the development of refractive surgery, where good uncorrected vision is frequently the final arbiter of success. We have progressed to the stage where the optic manipulation of the cornea, whether intentional or otherwise, can be understood in terms of a number of variables. These include the preparation and closure of the surgical wound, the choice of suture material, and both intraoperative and postoperative manipulations. Where these have failed and postoperative astigmatism still occurs, a number of surgical procedures are available to reduce the astigmatic error to an acceptable level.

Keratophakia--postoperative astigmatism.

Forty-nine cases of primary keratophakia and 13 cases of secondary keratophakia were analyzed for postoperative astigmatism. For primary cases, the surgically induced astigmatism was 1.55 D, whereas for secondary cases it was 0.19 D (insignificant). There was a tendency for both procedures to induce against-the-rule astigmatism, and both procedures were found capable of producing irregular astigmatism.

Epithelial ion transport in rabbit corneas following myopic keratomileusis.

In isolated rabbit corneas that had undergone lamellar keratectomy or myopic keratomileusis, the stimulation of chloride transport by 10(-5) M epinephrine was completely inhibited at 1 week following surgery. At 28 days following surgery, both groups responded to 10(-7) M epinephrine. The response to 10(-5) M amphotericin B was normal both at 1 week and at 28 days following surgery. We conclude that, although the Na-K pump was not affected by the lamellar keratectomy and cryolathing, that either the epithelial beta receptors and/or the cAMP pathway were temporarily inhibited for at least 1 week following surgery. A lamellar keratectomy, therefore, can have an adverse effect on the epithelial transport system of the corneal epithelium even though the epithelium may appear normal clinically.

Four-incision radial keratotomy for low to moderate myopia.

The first 112 consecutive eyes (75 patients) to undergo four-incision radial keratotomy (RK) performed by four surgeons were evaluated retrospectively. The preoperative myopia (spherical equivalent) ranged from -1.12 to -7.00 D (95% between -1.12 and -4.25 D). The preoperative uncorrected visual acuity was 20/100 or worse in 95% of the eyes. A six-month follow-up was achieved in 95% of the eyes and 45% were followed over one year. Following four incision RK, 79% of the eyes achieved 20/40 or better vision and 82% were corrected to within 1 D of emmetropia. Following repeat RK in 15 eyes (13%), 82% had uncorrected visual acuity of 20/40 or better, and 90% were corrected to within 1 D of emmetropia. Only 3.5% of the eyes were overcorrected by more than 1 D and only one eye had induced astigmatism greater than 1 D. For eyes with preoperative myopia up to -4.25 D over 90% achieved uncorrected visual acuity of 20/40 or better and were within 1 D of emmetropia following primary four incision RK and a second four incisions in 13 eyes (12%). Only 3.5% of the eyes in this group were overcorrected by more than 1 D. There were no serious complications.

A corneal mold to restore normal corneal dimensions.

A corneal mold is described that provides an MK corneal button of normal thickness and curvature from an edematous, post-mortem button. The uniform, processed tissue can then be used for experimental refractive surgery.

Retinal evaluation and treatment after refractive corneal surgery.

Refractive corneal surgery (a collective term used to describe a variety of surgical procedures that alter the refractive status of the eye through the surgical modification of corneal curvature) shows promise for use in situations where current methods of optical correction do not meet the patient's needs. This article reviews our experiences with the retinal evaluation of patients who have undergone corneal refractive surgery and offers recommendations for the treatment of retinal pathology after such surgery.

Dehydration of post-mortem eyes for practice and experimental surgery.

A technique has been developed that allows for rapid dehydration of the cornea of an intact globe. This technique results in a marked improvement in corneal clarity and visualization of anterior chamber structures. Treated eyes can be used for practice and experimental surgery.

Freezing increment in keratophakia.

In homoplastic keratomileusis, keratophakia, and epikeratophakia, the corneal tissue that provides the final refractive lenticule undergoes a conformational change when frozen. Because corneal tissue is composed primarily of water, an assumed value of 9.08% (approximate volumic percentage expansion of water when frozen) is frequently used for the increase in thickness, or freezing increment, rather than measuring it directly. We evaluated 32 cases of clinical keratophakia and found the increase in thickness to average 37 +/- 21%. In this series of 32 cases, the percentage of patients with a greater than 4 D residual refractive error was 16%. If an assumed freezing increment of 9.08% had been used, the percentage would have been 28%, with two-thirds of these 28% manifesting a marked undercorrection. Because of a lack of studies documenting the behavior of corneal tissue following cryoprotection and freezing, it is suggested that measurements be taken during homoplastic surgery to minimize the potential for significant inaccuracy in obtaining the desired optic result.