Journal Of Refractive And Corneal Surgery[JOURNAL]
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105 papers
Laser corneal surgery proceedings of the Third Annual Congress of the Summit International Laser User Group. Montreaux, Switzerland, September 17-19, 1993.
J Refract Corneal Surg · 1994 · PMID 7517295
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Cytotoxicity of viscoelastics on cultured corneal epithelial cells measured by plasminogen activator release.
Lindquist TD, Edenfield M
J Refract Corneal Surg · 1994 · PMID 7517294
BACKGROUND: Plasminogen activator has been shown to be released by epithelial cells following corneal injury. The demonstration of the release of plasminogen activator from cultured corneal epithelial cells has been used...
BACKGROUND: Plasminogen activator has been shown to be released by epithelial cells following corneal injury. The demonstration of the release of plasminogen activator from cultured corneal epithelial cells has been used for developing a cytotoxicity test, the Corneal Epithelial Plasminogen Activator test, which compares changes in the level of plasminogen activator in tissue culture media following chemical exposure as an index of chemical injury. METHODS: Cultured rabbit corneal epithelial cells were exposed to varying concentrations of several viscoelastics for 1 hour. Release of plasminogen activator into the tissue culture media following exposure to the viscoelastic agent was studied as an index of chemical injury. RESULTS: The least cytotoxicity to cultured rabbit epithelium was associated with those viscoelastic agents containing methylcellulose. A 1-hour exposure to most concentrations of methylcellulose and chondroitin sulfate (Phacote) and methylcellulose (Occucoat) demonstrated release of greater amounts of plasminogen activator than was seen following a similar exposure to balanced salt solution, suggesting the greatest protective effect of these two viscoelastics. In contrast, sodium hyaluronate and chondroitin sulfate (Viscoat) showed decreased amounts of plasminogen activator release after a 1-hour exposure to cultured corneal epithelial cells demonstrating cytotoxicity. Polyacrylamide (Orcolon) and most diluted preparations of sodium hyaluronate (Healon and Healon Yellow) showed only mild reductions in the release of plasminogen activator, whereas undiluted sodium hyaluronate preparations were nearly as cytotoxic as Viscoat. CONCLUSIONS: This study suggests that viscoelastic agents containing methylcellulose (Phacote and Occucoat) may be most protective of the corneal epithelium during ophthalmic surgery. The clinical success of several dilute viscoelastic solutions as tear substitutes was corroborated by the lack of cytotoxicity seen in this study. Viscoat and undiluted sodium hyaluronate preparations showed the greatest cytotoxicity to cultured rabbit corneal epithelium.
Excimer laser photorefractive keratectomy for myopia: comparison of 4.00- and 5.00-millimeter ablation zones.
O'Brart DP, Gartry DS, Lohmann CP … +2 more , Muir MG, Marshall J
J Refract Corneal Surg · 1994 · PMID 7517293
BACKGROUND: To date, there has been no systematic study of the effects of ablation zone diameter on the outcome of photorefractive keratectomy. To address these issues, we examined a series of eyes with bilateral correct...
BACKGROUND: To date, there has been no systematic study of the effects of ablation zone diameter on the outcome of photorefractive keratectomy. To address these issues, we examined a series of eyes with bilateral corrections using different-sized ablation zones. METHODS: Thirty-three patients underwent bilateral photorefractive keratectomy (Summit Excimed UV200, Waltham, Mass) with identical dioptric corrections in both eyes, except first eyes had 4.00-millimeter and second eyes had 5.00-millimeter ablation zones. Identical postoperative eyedrop regimens were used in both eyes of each subject and the interval between treatments was 12 months. The mean depth of the programmed central ablation was 24 microns in eyes treated with 4.00-millimeter and 39 microns with 5.00-millimeter zones. RESULTS: There was no statistically significant difference in the preoperative refraction between first and second eyes. Mean changes in refraction at 1, 3, 6, 9, and 12 months were significantly greater in eyes treated with 5.00-millimeter ablation diameters (p < .001). No eyes treated with 4.00-millimeter zones were overcorrected, but five eyes (15%) treated with 5.00-millimeter beams had a refraction greater than +1.00 diopter (D) at 12 months postoperatively. There was no significant difference in the amount of anterior stromal haze between the two eyes at any stage. In 14 patients, less night halo was noticed in the eye treated with a 5.00-millimeter zone. Using a computer program, halo measurements were made in both eyes of 12 patients whose pre- and postoperative refractions were within 0.50 D. The magnitude of halo was significantly less in eyes treated with 5.00-millimeter zones (p < .01). CONCLUSIONS: Despite greater depths of stromal ablation with 5.00-millimeter diameters, there was no increased anterior stromal haze or postoperative regression of refraction. The biological and physical constraints governing the optimum size of the photorefractive keratectomy ablation zone are discussed.
Excimer laser: a step-up in complexity and responsibility for the ophthalmic laser surgeon?
Krueger RR
J Refract Corneal Surg · 1994 · PMID 7517292
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FDA panel recommends conditional approval of excimer laser phototherapeutic keratectomy (PTK).
Waring GO
J Refract Corneal Surg · 1994 · PMID 7517291
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Corneal stability and avoidance of hyperopia following incisional keratotomy.
Casebeer JC
J Refract Corneal Surg · 1994 · PMID 7517290
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Aerosol application of cyanoacrylate adhesive.
Quillen DA, Rosenwasser GO
J Refract Corneal Surg · 1994 · PMID 7517289
BACKGROUND: Cyanoacrylate adhesive has been used to treat corneal perforations and stromal melting disorders. We examined the efficacy of aerosolization as a means of applying cyanoacrylate to the cornea. METHODS: Centra...
BACKGROUND: Cyanoacrylate adhesive has been used to treat corneal perforations and stromal melting disorders. We examined the efficacy of aerosolization as a means of applying cyanoacrylate to the cornea. METHODS: Central corneal perforations were created with a 1-millimeter trephine in cadaver eyes. A small amount of N-butyl cyanoacrylate was delivered to the perforation site via aerosol. Experiments were also conducted with cadaver eyes which had received lamellar keratectomies to stimulate corneal thinning disorders. RESULTS: Adequate seal of the 1-millimeter perforation was achieved following aerosol application of cyanoacrylate adhesive. In experiments conducted with eyes which had been perforated and those which received lamellar keratectomies, smooth anterior surface contours were achieved using the aerosol technique. CONCLUSIONS: Aerosolization may be an effective method of applying cyanoacrylate adhesive.
Electron microscopic evaluation of intrastromal corneal rings explanted from nonfunctional human eyes.
Quantock AJ, Assil KK, Schanzlin DJ
J Refract Corneal Surg · 1994 · PMID 7517288
BACKGROUND: Intrastromal corneal rings (ICRs) often exhibit small deposits in association with their suture holes. We assessed the morphology of four such deposits. METHODS: Four ICRs, explanted from nonfunctional human...
BACKGROUND: Intrastromal corneal rings (ICRs) often exhibit small deposits in association with their suture holes. We assessed the morphology of four such deposits. METHODS: Four ICRs, explanted from nonfunctional human eyes, were examined by scanning electron microscopy and transmission electron microscopy. RESULTS: The surface of the suture hole deposits consisted of a disorganized convolution of collagenous lamellae. Within individual lamellae, however, the collagen fibrils tended to orientate parallel with one another. The deposits consisted of an amorphous material interspersed with curved cellular processes, collagen fibrils of variable diameter, and proteoglycan macromolecules. CONCLUSIONS: We propose that the mechanism which regulates stromal remodeling is amended in the region of the ICR suture holes. Due to their location, suture hole deposits have no optical significance; however, evaluation of their morphology provides insights into the wound-healing properties of the corneal stroma following ICR insertion.
Evaluation of corneal thickness and endothelial cells before and after excimer laser photorefractive keratectomy.
Cennamo G, Rosa N, Guida E … +2 more , Del Prete A, Sebastiani A
J Refract Corneal Surg · 1994 · PMID 7517287
BACKGROUND: The possible endothelial damage induced by photorefractive keratectomy was investigated in myopic eyes. METHODS: A morphometric analysis of the endothelial cells was performed in 19 patients before and 2 mont...
BACKGROUND: The possible endothelial damage induced by photorefractive keratectomy was investigated in myopic eyes. METHODS: A morphometric analysis of the endothelial cells was performed in 19 patients before and 2 months after photorefractive keratectomy for the correction of various degrees of myopia. Central ultrasonic pachometry was also recorded at the same examination times. RESULTS: No significant changes (p = .816) of the endothelial cell density were found between preoperative and postoperative measurements. The pleomorphic index did not show any significant changes after treatment (p = .955). Central corneal thickness was reduced to a various extent (range from 50 microns to 250 microns) according to the amount of myopic correction intended. CONCLUSIONS: Our preliminary data suggest that photorefractive keratectomy for the correction of myopia does not induce endothelial cell damage, at least in the short term.
Visual function before and after photorefractive keratectomy for myopia.
Ambrosio G, Cennamo G, De Marco R … +3 more , Loffredo L, Rosa N, Sebastiani A
J Refract Corneal Surg · 1994 · PMID 7517286
BACKGROUND: To date, Snellen visual acuity and postoperative refraction have been used to evaluate the results of photorefractive keratectomy. However, other parameters, such as contrast sensitivity function and glare, m...
BACKGROUND: To date, Snellen visual acuity and postoperative refraction have been used to evaluate the results of photorefractive keratectomy. However, other parameters, such as contrast sensitivity function and glare, may be affected by refractive surgery and lead to unsatisfactory visual performance. This prospective study is aimed at evaluating the effect of photorefractive keratectomy on contrast sensitivity function and glare. SUBJECTS AND METHODS: Static contrast sensitivity function, dynamic contrast sensitivity function, and glare sensitivity were evaluated in 22 myopic eyes before as well as 1, 3, and 6 months after photorefractive keratectomy. The eyes tested were divided into three groups, according to the amount of myopia: group I, from -4.00 to -8.00 diopters (D); group II, from -8.25 to -11.00 D; group III, from -11.25 to -20.00 D. RESULTS: Both static and dynamic contrast sensitivity function at the intermediate spatial frequencies were altered at 1 month after photorefractive keratectomy, with a trend toward recovery at 3 and 6 months postoperatively. Glare sensitivity was not significantly affected by surgery. CONCLUSIONS: Contrast sensitivity function and glare testing may show abnormalities in the presence of optimal visual and refractive results. These tests may result especially important for the evaluation of new refractive surgical procedures.
Corneal power correction factor for photorefractive keratectomy.
Mandell RB
J Refract Corneal Surg · 1994 · PMID 7517285
BACKGROUND: Studies of corneal power changes resulting from photorefractive keratectomy generally rely on keratometer or videokeratograph measurements. These instruments convert corneal radius of curvatures values to opt...
BACKGROUND: Studies of corneal power changes resulting from photorefractive keratectomy generally rely on keratometer or videokeratograph measurements. These instruments convert corneal radius of curvatures values to optical powers by means of the single refracting surface formula, which incorporates an index of refraction value of 1.3375. This index approximates that of the tears but not the 1.376 index of the corneal epithelium or stroma. A hypothetical optical model was used to determine the most appropriate index to be chosen with respect to corneal power calculations relative to photorefractive keratectomy. METHODS: The contribution of each refractive element in the tear lens-corneal surface to the total power of the eye was calculated in order to identify which index of refraction was most appropriate for the corneal power calculation. RESULTS: The outer tear surface has significant optical power but the tear layer as a whole has nearly zero power due to the offsetting negative power of the posterior test surface. There is no significant difference in the effective power of light leaving the corneal anterior surface when considered with or without the tear layer. Photorefractive keratectomy changes the epithelium and anterior surface of the corneal stroma, but does not affect the posterior stroma or other ocular media. Hence the refractive index for the corneal epithelium or stroma of 1.376 should be used in converting radius to optical power values. The error in assuming a corneal index of 1.3375 is a constant proportion equal to 11.4% of the corneal power reading. CONCLUSIONS: Photorefractive keratectomy presents a situation in which the actual corneal refractive index of 1.376 should be used for correct corneal radius to power conversions. This may be accomplished by changing the index value in the instrument algorithm for keratometry and videokeratography to 1.376 or by adding a correction factor of either 11.4% of the regular reading to its value or multiplying by the factor 1.114. In other applications of keratometry or videokeratography, the index 1.3375 may be more appropriate.
Clear lens extraction and intraocular lens implantation in normally sighted hyperopic eyes.
Siganos DS, Siganos CS, Pallikaris IG
J Refract Corneal Surg · 1994 · PMID 7517284
BACKGROUND: Currently used corneal refractive procedures do not offer a perfect solution for high hyperopia. This article proposes clear lens extraction and intraocular lens (IOL) implantation for the correction of high...
BACKGROUND: Currently used corneal refractive procedures do not offer a perfect solution for high hyperopia. This article proposes clear lens extraction and intraocular lens (IOL) implantation for the correction of high hyperopia. METHODS: Extracapsular clear lens extraction and posterior chamber IOL implantation was performed in 10 normally sighted eyes of five patients with a hyperopic spherical equivalent refraction between +7.88 and +9.75 D. The follow-up period was 18 months. RESULTS: Mean uncorrected visual acuity improved from count fingers to 20/25. All eyes saw 20/30 or better without correction. Postoperative correction ranged from -0.37 to +0.50 diopters (mean, 0.01). The mean endothelial cell loss percentage at 18 months was 11.2% +/- 1.87% (range, 8% to 13%). CONCLUSIONS: The excellent results of contemporary cataract surgery, the reduced morbidity, patient satisfaction, as well as accuracy and rapid stability of the refraction suggest that clear lens extraction and IOL implantation are useful refractive procedures for the correction of high hyperopia.
Characterization of the inherent error in a spherically-biased corneal topography system in mapping a radially aspheric surface.
Roberts C
J Refract Corneal Surg · 1994 · PMID 7517283
BACKGROUND: Accurate measurement of corneal topography is crucial for many clinical applications. Also, the human cornea is known to be an asphere. Therefore, the purpose of this study was to quantitatively evaluate the...
BACKGROUND: Accurate measurement of corneal topography is crucial for many clinical applications. Also, the human cornea is known to be an asphere. Therefore, the purpose of this study was to quantitatively evaluate the accuracy of the EyeSys Corneal Analysis System in measuring a radially aspheric test surface and characterize the error function. METHODS: Curvature of a calibrated ellipsoid was determined using three techniques: 1) calculating theoretically, 2) modeling with a spherically-biased algorithm, and 3) measuring experimentally using the EyeSys system, both with the surface aligned and under conditions of misalignment. RESULTS: The inherent error steadily increased from center to periphery, with a maximum error greater than 3.00 diopters at a radius of 4 mm for an eccentricity of 0.5 and apical radius of curvature of 7.5 mm. CONCLUSIONS: The EyeSys Corneal Analysis System does not accurately measure the instantaneous radii of curvature of an ellipsoid. Misalignment error is small compared to the inherent error due to a spherically-biased reconstruction.
Optimists predict photorefractive keratectomy approval in 1994.
Moretti M
J Refract Corneal Surg · 1994 · PMID 7517785
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First ever eye donor: a lesson from Indian history and Kannappa Nayanar.
Basti S
J Refract Corneal Surg · 1994 · PMID 7517784
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Refractive corneal surgery with the Draeger rotary microkeratome in human cadaver eyes.
Stonecipher KG, Parmley VC, Rowsey JJ … +3 more , Fowler WC, Nguyen H, Terry M
J Refract Corneal Surg · 1994 · PMID 7517783
BACKGROUND: Instrumentation for performing a uniform lamellar keratoplasty has been undergoing various stages of refinement. Reliable reproduction and uniform thickness and diameter of lamellar resections is required bef...
BACKGROUND: Instrumentation for performing a uniform lamellar keratoplasty has been undergoing various stages of refinement. Reliable reproduction and uniform thickness and diameter of lamellar resections is required before lamellar refractive keratoplasty can be considered safe and effective. METHODS: The authors used the Draeger rotary microkeratome with mechanical blade advance for lamellar dissections in 61 human cadaver eyes prepared by injecting Swinger-Kornmehl (SK) solution into the anterior chamber to a pressure of 35 to 40 mm Hg and by soaking for 30 minutes in SK solution. Spacer sizes of 0.25 to 0.40 units were utilized using an anterior lamellar disc diameter estimate between 8.0 and 8.5 mm and a stromal lamellar disc diameter estimate between 5.5 and 6.5 mm. Preoperative pachometry, anterior and stromal lamellar disc thicknesses, and anterior and stromal lamellar disc diameters were measured. RESULTS: The Draeger unit created anterior lamellar thickness between 100 and 268 microns. Stromal lamellar disc thicknesses were consistently between 90 and 161 microns. The continuous, unidirectional, rotary blade and the uniform mechanical advance of the instrument produced a generally uniform bed as evaluated by scanning electron microscopy, although undulations were still present. CONCLUSION: The Draeger microkeratome produced regular lamellar dissections; however, predictability of the thickness of the lenticules varied 10% to 20%, and of the diameter, 1.5% to 15%. Predictability improved with experience. This variability may reduce predictability of refractive outcome.
Does the progressive increasing effect of radial keratotomy (hyperopic shift) correlate with undetected early keratoconus?
Saragoussi JJ, Pouliquen YJ
J Refract Corneal Surg · 1994 · PMID 7517782
Keratoconus suspect is a new clinical entity revealed by videokeratography. We perform systematic videokeratography on all candidates for refractive surgery, and have identified a keratoconus suspect in more than 10% of...
Keratoconus suspect is a new clinical entity revealed by videokeratography. We perform systematic videokeratography on all candidates for refractive surgery, and have identified a keratoconus suspect in more than 10% of eyes. A lot of patients with undetected early keratoconus have been operated on since 1980. We suggest a possible correlation between early keratoconus suspect and the hyperopic shift following radial keratotomy. Our arguments are based on clinical observations, knowledge about pathogenesis of keratoconus and the mechanism of action of radial keratotomy, and epidemiological considerations.
Intraoperative pachometry during automated lamellar keratoplasty: a preliminary report.
Casebeer JC, Slade SG, Dybbs A … +1 more , Mahanti RL
J Refract Corneal Surg · 1994 · PMID 7517781
BACKGROUND: The hinge technique greatly improves the results of automated lamellar keratoplasty but makes it impossible to measure the thickness of the corneal cap with a micrometer. We developed a technique of measuring...
BACKGROUND: The hinge technique greatly improves the results of automated lamellar keratoplasty but makes it impossible to measure the thickness of the corneal cap with a micrometer. We developed a technique of measuring cap and stromal disc thickness with a pachometer and compared the results with those obtained with a micrometer. METHODS: Measurements of the thickness of the stromal disc and/or corneal cap were taken with the Mitutoyo micrometer and the Chiron Corneo-Gage System III pachometer in five myopic and three hyperopic cases undergoing automated lamellar keratoplasty with complete cap resection. The intended postoperative refraction was plano. Postoperative refractions were taken at two months. RESULTS: In most cases, the corneal cap measured thinner while the stromal disc measured thicker by the micrometer than by the pachometer because of the hydration status of the stromal bed. In both myopic and hyperopic cases, the thickness measurements taken with the pachometer correlated better with the postoperative spherical equivalent values than those taken with the micrometer. CONCLUSIONS: The thickness measurement of corneal resections by both micrometry and pachometry is greatly influenced by tissue hydration status. When hydration is similar, the pachometer provides more accurate thickness readings than does the micrometer, as determined by correlations with intended refractive results.
Viability of bacteria in glycerin and ethanol preserved sclera.
Dailey JR, Rosenwasser GO
J Refract Corneal Surg · 1994 · PMID 7517780
BACKGROUND: Sclera is commonly preserved in glycerin or ethanol before being used for ophthalmic surgery. The purpose of this study was to determine the ability of bacteria to survive in sclera preserved in glycerin or e...
BACKGROUND: Sclera is commonly preserved in glycerin or ethanol before being used for ophthalmic surgery. The purpose of this study was to determine the ability of bacteria to survive in sclera preserved in glycerin or ethanol. METHODS: Fresh sclera was inoculated with Staphylococcus aureus, Streptococcus pneumoniae, or Pseudomonas aeruginosa and transferred to preservative vials containing glycerin, 95% ethanol, or trypticase soy broth (control) and stored at room temperature. Pieces of sclera were removed from preservative at designated intervals over a 14-day period. The sclera was then homogenized, plated on blood agar, and incubated at 37 degrees C. Colonies were counted at 24, 48, and 72 hours. RESULTS: S. pneumoniae, P. aeruginosa, and S. aureus were recovered from glycerin preserved sclera for up to 12 hours, 1.5 days, and 8 days, respectively. No bacteria was recovered from the ethanol preserved sclera. CONCLUSIONS: Bacteria cannot be recovered from ethanol preserved sclera but can survive in glycerin preserved sclera for at least 8 days. Ethanol may offer advantages over glycerin as a scleral preservative due to its greater antibacterial activity.
Traumatic corneal abrasions following photorefractive keratectomy.
Salz JJ
J Refract Corneal Surg · 1994 · PMID 7517779
BACKGROUND: During excimer laser photorefractive keratectomy, central Bowman's layer and superficial stroma are removed. A potential disadvantage of this technique is whether proper epithelization of the cornea will occu...
BACKGROUND: During excimer laser photorefractive keratectomy, central Bowman's layer and superficial stroma are removed. A potential disadvantage of this technique is whether proper epithelization of the cornea will occur in the event of a corneal abrasion. A potential advantage of photorefractive keratectomy over radial keratotomy in the event of blunt trauma is the presumably sound structural integrity of the cornea following superficial removal of stroma in photorefractive keratectomy compared to the weakened cornea following deep incisions in radial keratotomy. METHODS: We report two patients who sustained corneal abrasions from blunt trauma to the eye and orbit following photorefractive keratectomy--one following a fist injury and the other following a karate kick. RESULTS: In both patients, the corneal abrasions healed without incident and without recurrent erosions and both corneas remained intact. CONCLUSIONS: Corneal abrasion following trauma in two patients who has undergone photorefractive keratectomy healed as expected in a normal cornea. Although it is uncertain whether the trauma in these patients would have been sufficient to rupture radial keratotomy incisions, as would be expected from a superficial photorefractive keratectomy, the corneas remained intact following blunt trauma.
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