Phakic anterior chamber lenses for the correction of myopia.
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Anterior Chamber↗
Biomedical subjects
T P Werblin
Publications and source records attributed to T P Werblin.
Casebeer System for refractive keratotomy: patient satisfaction.
PURPOSE: To evaluate patient satisfaction 3 years after radical keratotomy (RK) using the Casebeer nomograms. SETTING: The Werblin Center, Princeton, West Virginia. METHODS: This study assessed the satisfaction of 96 patients who had bilateral distance correction by RK using the Casebeer System. The cases were part of the first 241 consecutive refractive keratotomy procedures (N = 128 patients) performed by one surgeon. Ninety-nine percent of the 96 patients in this study completed a questionnaire on satisfaction and visual symptoms 3 years postoperatively. A separate control population of 105 consecutive patients about to have RK surgery were asked to complete a questionnaire about their preoperative symptoms. RESULTS: Ninety-eight percent of patients were very to moderately satisfied 3 years after the procedure, 99% said they would have surgery again if given the chance, and 96% said they would recommend it to others. However, 69% stated they had mild to very severe symptoms 3 years postoperatively compared with 28% in the control group. CONCLUSION: Despite an extremely high degree of patient satisfaction, about 99%, the 1% dissatisfaction rate seen in this study could have be very significant in this young, potentially litigious patient population.
Adult↗
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.
Adult↗
Hyperopic shift after refractive keratotomy using the Casebeer System.
PURPOSE: To determine the degree of hyperopic shift following refractive keratotomy. SETTING: The Werblin Center, Princeton, West Virginia. METHODS: The results of 241 consecutive radial/astigmatic keratotomy procedures in 128 patients were studied. All procedures were performed using Casebeer nomograms. Refractive follow-up information was obtained for 78% of patients at 3 months (range 1 to 6 months), 1 year (range 6 to 21 months), and 3 years (range 30 to 44 months). RESULTS: Overall, the amount of hyperopic change decreased significantly (P < .05) during the 3 year period, from + 0.34 diopters (D) per year to + 0.12 D per year. Eyes with more than 6.0 D of preoperative intended correction were more unstable (+ 0.49 D in the first year and + 0.44 D in the second and third years) than eyes with less than 5.0 D (+ 0.27 D and + 0.05, respectively). CONCLUSION: Because the average magnitude of the hyperopic shift was + 0.6 D in the first 3 years after surgery, a slight undercorrection, -0.5 D to -0.7 D, should be the refractive endpoint for primary and enhanced refractive keratotomy surgery.
Follow-Up Studies↗
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.
Adult↗
Persistent hemorrhage after extracapsular surgery associated with excessive aspirin ingestion.
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Aged↗
Synthetic keratophakia for the correction of aphakia.
Although the majority of aphakic patients will have intraocular lens implants (IOLs), there are several groups of patients for whom IOLs are not indicated. Synthetic keratophakia for the correction of aphakia has several inherent advantages over alternative forms of refractive surgery which use lathed corneal tissue. For example, the ability to produce a synthetic lens to precise specifications before surgery is a dramatic advantage over the use of lathed tissue lenses whose refractive properties cannot be determined until weeks or months after the lens is in place on the recipient cornea. Synthetic materials appear to behave in a predictable manner and are biocompatible. Both polysulfones and hydrogel materials can be used to correct aphakia in clinical situations where other modalities are less appropriate.
Animals↗
Keratoconus in a rhesus monkey.
A 15-year-old female rhesus monkey was observed to have bilaterally thinned and prominently curved corneas. Slit lamp observations, pachymetry, keratometry, and corneoscopy were consistent with a diagnosis of keratoconus, a relatively common corneal dystrophy in humans heretofore not described in a subhuman primate.
Animals↗
Myopic hydrogel keratophakia. Improvements in lens design.
In order for a refractive surgical procedure to be generally accepted, it must give a predictable result as well as generate a suitable optical surface. Previously, in a non-human primate model, we showed that hydrogel intracorneal lenses could flatten the cornea and thereby be used as a potential treatment for myopia. Over 20 D of central corneal flattening was observed in some cases. It was evident that the major corneal flattening occurred only in a very small area covered by the first corneascopic ring and that this area was irregular in that an elliptical reflection was generally obtained. We herein present the results of myopic hydrogel lens design modification. By enlarging the size of the lens and optical zone, the central corneal flattening became more regular as judged by corneascopic analysis. With the most recent lens designs, animals with high-minus implants showed circular corneascopic images with an average of 10.0 D of central flattening. This observation of corneal flattening was confirmed with autorefractor readings (average, -8.5 D) and keratometric readings (average, -9.0 D). These results are compared with earlier lens implants 5.5 mm in diameter where flattening was documented by reading the central corneascopic ring and could not be confirmed with either keratometric or autorefractor data. We feel these preliminary attempts at lens design modification have significantly enhanced the potential for future clinical application of this technique.
Animals↗
Failed epikeratophakia graft.
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Corneal Transplantation↗
Fetal adenoma of the pigmented ciliary epithelium associated with persistent hyperplastic primary vitreous.
A 1.5-year-old girl presented with a peripheral iris mass. When the girl was 3 years old, the lesion was excised after it had manifested significant growth. A stalk of fibrovascular tissue was noted to extend from the lesion to the optic disc. Histopathologically, the tumor was a well-circumscribed, pigmented ciliary body adenoma. Electron microscopy revealed characteristic neuroepithelial melanosomes, distinct from those of choroidal melanocytes, and occasional annulate lamellae. A fibrovascular membrane extended over the tumor surface and was adherent to lens capsule. The association of this adenoma with a persistent stalk of primary vitreous indicates a congenital origin of this tumor. Both adenoma and adenocarcinoma of the pigmented and nonpigmented ciliary epithelium tend to be disorders of adults. The authors report the youngest presentation of a pigment epithelium adenoma, the only well-documented case associated with persistent hyperplastic primary vitreous, and the only documentation of annulate lamellae in a ciliary body tumor.
Adenoma↗
Pathology of corneal hydrogel alloplastic implants.
Hydrogel keratophakia is a new form of lamellar refractive surgery which, in theory, can deal with almost all forms of refractive error. We examined the histopathological effects of several types of hydrogel materials on the cornea of non-human primates. With the exception of one type of hydrogel material, which was associated with endothelial cell degeneration, only minor histopathologic changes were seen up to a maximum of one year of observation, including thinning of the epithelium and decreased population of stromal keratocytes. These changes did not correlate with any clinical abnormalities. Additional extensive preclinical testing and eventual human clinical trials will determine the safety and efficacy of this procedure.
Animals↗
Histological study of epikeratophakia in primates.
Two primate corneas were analyzed histologically 22 and 25 months after epikeratophakia surgery. Keratocytes had migrated from the host cornea into the lenticule through the surgical disruption of the host Bowman's membrane; the lenticule with the wider connection to the host cornea appeared to have more complete keratocyte repopulation. The lenticule stroma and host Bowman's membrane were continuously apposed along the interface, with a basement membrane-like material composed of collagen fibrils and amorphous matrix filling the interstices.
Animals↗
Compensating for thermally caused dimensional changes in the cryolathe.
Dimensional changes in the Barraquer cryolathe , resulting from contraction due to refrigeration, can exert a considerable effect on the dimensions of the lathed lenticule . We have devised a simple technique for re- zeroing the cryolathe after freezing. This procedure negates the effects of the dimensional changes and thereby improves the accuracy of shaping the lenticules .
Calibration↗
Myopic correction using alloplastic implants in non-human primates--a preliminary report.
Hydrogel keratophakia has been studied in a non-primate model in an attempt to develop a more predictable form of myopic refractive surgery. Although the largest potential clinical use for this form of surgery is for the correction of myopia, currently available surgical techniques are not nearly as predictable as non-surgical devices such as spectacles and contact lenses. In this paper, hydrogel lenses, implanted in non-human primate corneas, were used for the first time to flatten the anterior corneal surface as would be required for the correction of myopia. Up to 9 diopters of correction was obtained. Little change in corneal astigmatism was found. The technical aspects of the surgery are quite simple, and the corneas healed rapidly and have excellent clarity. Extensive primate testing will be necessary to determine the accuracy of this procedure before clinical trials should be undertaken.
Animals↗
Measurement of intraocular pressure after epikeratophakia.
New forms of refractive surgery result in corneas that are nearly doubled in thickness. To test the reliability of standard instrumentation for the measurement of intraocular pressure in such eyes, the MacKay-Marg tonometer was used on eye bank eyes with and without epikeratophakia lenticules and/or bandage contact lenses. The Goldmann applanation prism in the hand-held Perkins portable tonometer and the MacKay-Marg tonometer were used to measure IOP in vivo in a primate eye with an epikeratophakia graft. Measurements were compared with actual intraocular readings from a transducer. The MacKay-Marg tonometer was reliable at pressures above 20 mm Hg; the extra thickness of the graft and/or the rigidity of the contact lens impaired the accuracy below 20 mm Hg. The Goldman tonometer was accurate over the entire range of pressures.
Animals↗
Epikeratophakia: techniques, complications, and clinical results.
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Animals↗
Epikeratophakia: existing limitations and future modifications.
The predictability of optical correction has been a problem for all forms of refractive corneal surgery in epikeratophakia, changes in graft dimensions and surgical technique improved accuracy, but several problems still exist in cryolathing preserved corneal tissue. Preserved corneal tissue is quite oedematous and when frozen on the cryolathe, assumes an irregular shape. A mechanical technique to dehydrate tissue was developed which yields corneal tissue which behaves in a predictable fashion. The use of donor corneal tissue in refractive surgery has certain inherent limitations. There is no way of measuring the power of the lathed corneal lens prior to surgery; the power is a function of the shape the lens will take in vivo. The ability to supply large numbers of donor corneal buttons may be an impractical task should this type of surgery become widely used. The use of alloplastic lenses should overcome most of these difficulties.
Cornea↗