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Biomedical subjects

H J Shammas

Publications and source records attributed to H J Shammas.

At least 19 recordsLinked to original sources
PubMed1997

Topical and subconjunctival anesthesia for phacoemulsification: prospective study.

PURPOSE: To evaluate the efficacy and safety of topical and subconjunctival anesthesia for phacoemulsification and to compare the results with those of retrobulbar-peribulbar anesthesia. METHODS: This prospective study evaluated 402 patients having phacoemulsification during 60 surgical sessions. Patients were randomly assigned to receive a topical and subconjunctival injection of lidocaine 4% or a retrobulbar injection of the same anesthetic. RESULTS: Patients who received topical and subconjunctival anesthesia received less anesthetic (0.25 versus 3.25 mL) and had fewer side effects from the intravenous sedation and a lower incidence of capsular rupture associated with positive vitreous pressure during surgery (0 versus 2.9%). The difference in postoperative discomfort was not statistically significant, and there were no complications resulting from needle insertion. CONCLUSION: Topical and subconjunctival anesthesia using lidocaine 4% was as effective as retrobulbar and peribulbar anesthesia for routine phacoemulsification. In addition, fewer anesthetic drugs and less patient sedation were required, and there were fewer intraoperative and postoperative complications.

Administration, Topical↗
PubMed1996

Anterior intraocular lens dislocation after combined cataract extraction trabeculectomy.

PURPOSE: To evaluate the incidence, cause, and effect of intraocular lens (IOL) dislocation after combined cataract extraction and trabeculectomy. SETTING: An ophthalmic ambulatory surgery center in Lynwood, California. METHODS: This retrospective study comprised 150 patients with open-angle glaucoma who had either planned extracapsular cataract extraction (ECCE) (n = 96) or phacoemulsification (n = 54) combined with IOL implantation and trabeculectomy. I reviewed type of cataract extraction, preoperative glaucoma medications, axial length, and amount of filtration achieved postoperatively. RESULTS: The lens dislocated in 20 eyes (13.3%), with the highest incidence after planned ECCE (18.7%) and the lowest after phacoemulsification with capsulorhexis (3.7%). Eighteen of 30 eyes (60%) that had excessive filtration also had IOL dislocation. Mean induced postoperative myopia in eyes with lens dislocation was-2.25 diopters (D) +/- 0.55 (SD). CONCLUSIONS: Anterior IOL dislocation was related to increased postoperative filtration and was more common after planned ECCE. In all cases, it caused a distorted pupil, posterior synechias, and induced myopia of over -1.00 D.

Anterior Chamber↗
PubMed1994

Photorefractive keratectomy for the correction of myopia and astigmatism.

Photorefractive keratectomy corrects myopia with or without astigmatism by decreasing the refractive power of the central cornea. The Colliac matrix formula determines the anterior corneal radius of curvature expected to achieve emmetropia. We used the formula as an algorithm for the computer-controlled delivery of the laser beam. The formula was evaluated by using theoretical and clinical cases. We examined the relationship between the correction induced by photorefractive keratectomy, the diameter of ablation zone, and the thickness of the ablated corneal lenticule on the optical axis. Comparison between attempted and achieved keratometric readings showed the accuracy of the formula to be in the order of +/- 0.75 diopter.

Adult↗
PubMed1994

Integrated iseikonic equation for intraocular lens power calculations.

I present a simplified equation to calculate the iseikonic intraocular lens power and the resultant refractive error needed to achieve iseikonia with 5% tolerance limits. Iseikonic lens power calculations are indicated in the presence of a unilateral cataract and a phakic fellow eye. Iseikonia is often achieved by leaving the operated eye more myopic than the fellow eye. The induced myopia, with 5% tolerance limits, ranges from -0.75 +/- 2.75 diopters (D) for a posterior chamber lens to -2.40 +/- 2.75 D for an anterior chamber lens.

Humans↗
PubMed1993

Optics for photorefractive keratectomy.

Matrix calculations are applied to Gaussian optics in the study of myopic correction by photorefractive keratectomy. The Colliac matrix formula determines the postoperative anterior curvature radius of the treated cornea. It also calculates the maximal depth of the removed corneal tissue and the ablation zone diameter needed to achieve emmetropia.

Adult↗
PubMed1990

Clinical evaluation of the Bio-Pen for axial length measurement.

The axial length of 207 eyes was evaluated in a clinical comparison between the Bio-Pen biometric ruler and the Kretz 7200 MA A-scan unit. The overall correlation was 0.99. The Bio-Pen measurement averaged 0.056 mm shorter than the Kretz. The difference was statistically significant (P less than .0001). The Bio-Pen was found to be a convenient and clinically accurate biometer.

Biometry↗
PubMed1989

Mature cataracts in eyes with unilateral axial myopia.

Seven patients with unsuspected unilateral axial myopia developed a cataract in the longer eye. Vision deteriorated in all cases between the ages of 40 and 55 years. Bilateral axial length measurements were necessary for the diagnosis and revealed a difference of 4.5 mm to 6.7 mm between the two eyes. Five cases had a mature cataract and had extracapsular cataract extraction; surgery restored isometropia, improved the visual acuity to 20/200 or better, and enlarged the field of vision. All patients were amblyopic in the cataractous eye.

Adult↗
PubMed1988

Accuracy of lens power calculations with the biconvex and meniscus intraocular lenses.

In a prospective study, intraocular lens power calculations were within +/- 0.50 diopter of the final refraction in 77 of 88 eyes (87.5%) with a biconvex lens and in 41 of 90 eyes (45.5%) with a meniscus lens. The more precise power calculations with the biconvex intraocular lens seemed to be related to the superior optical design of the lens, with its close configuration to a normal crystalline lens.

Cataract Extraction↗
PubMed1984

A comparison of immersion and contact techniques for axial length measurement.

A prospective study was conducted on 180 eyes to evaluate axial length measurements obtained with both contact and immersion techniques. Each eye was measured with the Ocuscan-DBR (contact), the Ocuscan-400 (immersion), and the Kretz 7200 MA (immersion) units. Axial length measurements obtained by the two methods were highly reproducible. Axial length measurements obtained with the contact technique were shorter than measurements obtained with the immersion technique by an average of 0.24 mm.

Anthropometry↗
PubMed1983

Secondary implantation of anterior chamber lenses.

One hundred and sixty-nine aphakic eyes underwent secondary implantation of anterior chamber lenses. The postoperative visual acuity decreased by one or more lines in five eyes (3%), remained the same in 71 eyes (42%), and improved by one or more lines in 93 eyes (55%). The presence of macular degeneration, background diabetic retinopathy, and open-angle glaucoma with a cup-to-disc ratio of 0.6 or less did not contribute to any visual deterioration.

Anterior Chamber↗
PubMed1982

Axial length measurement and its relation to intraocular lens power calculations.

The axial length was measured in five hundred consecutive cases using the Kretz 7200 MA ultrasound unit and an immersion technique. The reproducibility of the measurements was within +/- 0.2 mm when performed manually, and within +/- 0.05 mm when performed electronically. Intraocular lens power calculations were performed using a modification of Colenbrander's formula. We predicted within + 1 diopter in 78.8% of the cases. The accuracy was up to 83% when the axial length ranged between 23.0 and 25.0 mm. Stronger power lenses were implanted in shorter eyes and weaker power lenses in longer eyes, necessitating the use of a fudge factor. Surgeons using an immersion technique for axial length measurements should use formulas yielding stronger power lenses, such as Binkhorst's formula or our modification of Colenbrander's formula, with a fudge factor for short and long eyes.

Biometry↗
PubMed1982

The fudged formula for intraocular lens power calculations.

The formula presented is a modification of Colenbrander's formula. The formula yields a 0.70 diopter stronger power emmetropizing lens for a 23.0 mm eye. It also fudges the axial length by subtracting 0.1 mm for each 1.0 mm longer than 23.0 mm, and by adding 0.1 mm for each 1.0 mm shorter than 23.0 mm. Axial length was measured using immersion A-scan technique. In our prospectively tested group, the adjusted formula predicted implant power within +/- 1.00 diopter in 95% of eyes.

Biometry↗
PubMed1981

Cystoid macular edema following secondary lens implantation.

We reviewed 224 cases that had undergone secondary lens implantation. Cystoid macular edema occurred in 16 (7.1%) cases; edema was transient in 14 (6.3%) cases and permanent in two (0.8%) cases. Three factors seem to affect the incidence of CME: time lapse between cataract extraction and lens implantation; a positive preoperative fluorescein angiogram; and vitreous loss during lens implantation--if implantation is performed within a year of cataract extraction. Two eyes with pre-existing CME and a functional vision of 20/100 or better deteriorated to 20/200 or less after secondary lens implantation due to permanent macula edema. However, the incidence of postoperative CME can be as low as 1.3% if the macula is clear on the preoperative fluorescein angiogram and if surgery is performed no sooner than one year after cataract extraction.

Adult↗
PubMed1981

Traumatic fracture of a Choyce-style anterior chamber lens.

Accidental blunt trauma to a pseudophakic eye fractured the Choyce-style lens which had been implanted 11 months previously. This lens was removed, and its fracture was examined microscopically and duplicated experimentally using a torque-loading force and a shock-loading force. The nature and occurrence of lens fracture in situ depends on the direction of trauma.

Aged↗
PubMed1981

Melanocytoma of the ciliary body.

A 57-year-old Caucasian woman was found, on a routine ophthalmoscopic examination, to have a pigmented ciliary body mass suggestive of a malignant melanoma. The eye was enucleated primarily because a radioactive phosphorus test yielded a 79% greater uptake over the lesion than over a control area-a result regarded as positive at that time. Histopathologically, the lesion proved to be a benign melanocytoma of the ciliary body. Electron microscopy clearly revealed a large complement of inflammatory cells (macrophages) within the tumor. This case reemphasizes the advisability of carefully documenting tumor growth before enucleating eyes harboring pigmented lesions.

Ciliary Body↗