Accuracy of Toric Intraocular Lens Calculations Using Estimated Versus Measured Posterior Corneal Astigmatism

PURPOSE

To compare the prediction accuracy of toric intraocular lens calculations using estimated vs measured posterior corneal astigmatism (PCA).

DESIGN

Retrospective case series.

METHODS

A total of 110 eyes of 110 patients with uncomplicated toric intraocular lens implantation were included in this study. Predicted postoperative refractive astigmatism was calculated with the Barrett Toric Calculator using the estimated PCA (E-PCA), the measured IOLMaster 700 PCA (I-PCA), and the measured Pentacam PCA (P-PCA). Refractive astigmatism prediction errors (RA-PEs), including their trimmed (tr-) centroid (mean vector), spread (precision), tr-mean absolute RA-PE (accuracy), and percentage within a certain threshold, were determined using vector analysis and compared between groups.

SETTING

University Eye Clinic, Maastricht University Medical Center+, the Netherlands.

RESULTS

The tr-centroid RA-PEs of the E-PCA (0.02 diopter [D] at 82.2°), the I-PCA (0.08 D at 35.5°), and the P-PCA (0.09 D at 69.1°) were significantly different from each other (P < .01), but not significantly different from zero (P = .75, P = .05, and P = .05, respectively). The E-PCA had the best precision (tr-mean 0.40 D), which was not significantly lower than the I-PCA (0.42 D, P = .53) and P-PCA (0.43 D, P = .06). The E-PCA also had the best accuracy (0.40 D), which was not significantly different from the I-PCA (0.42 D, P = .26) and significantly better than the P-PCA (0.44 D, P < .01). The precision and accuracy of the I-PCA did not significantly differ from those of the P-PCA. There were no statistically significant differences in the percentage of eyes within a certain absolute RA-PE threshold.

CONCLUSIONS

The Barrett Toric Calculator using the E-PCA, I-PCA, or P-PCA showed a comparable prediction of postoperative refractive astigmatism in standard clinical practice.

Comparison of biometry measurements and intraocular lens power prediction between 2 SS-OCT-based biometers

PURPOSE

To evaluate the agreement in biometry measurements and intraocular lens (IOL) power prediction between the Eyestar 900 and the IOLMaster 700.

SETTING

Institutional.

DESIGN

Retrospective comparative study.

METHODS

Patients were evaluated before cataract surgery using both devices on the same visit. Axial length, anterior and posterior keratometry, anterior chamber depth, corneal diameter (CD), central corneal thickness, and lens thickness were recorded by both devices. The agreement in measurements and in IOL power calculations was evaluated using the Barrett Universal II (BU-II) formula with either predicted or measured posterior keratometry.

RESULTS

In total, 402 eyes of 402 consecutive patients were included. The mean age was 72.0 ± 9.2 years. Clinically, mean differences in measured variables were small, albeit slightly larger for posterior flat and steep keratometry (0.43 diopters [D] and 0.42 D, respectively). The measurement correlation and agreement between the devices were good for all variables with slightly lower agreement in CD measurements. Consistent bias was seen in measurements of posterior flat and steep keratometry. Good agreement was also found in anterior and posterior astigmatism measurements. Good IOL power calculation agreement was found using either predicted posterior keratometry (95% limits of agreement [LoA] of -0.40 to +0.30 D) or measured posterior keratometry (95% LoA of -0.45 to +0.40 D). The agreement was within ±0.5 D in 394 eyes (98.0%) using predicted posterior keratometry and in 386 eyes (96.0%) using measured posterior keratometry.

CONCLUSIONS

The Eyestar 900 and the IOLMaster 700 show strong agreement in biometry measurements and IOL power prediction by the BU-II formula using either standard or total corneal keratometry and can be used interchangeably.

Autorefraction as an Objective Method to Evaluate Accuracy of Intraocular Lens Calculation Formulas

PURPOSE

To compare the spherical equivalent (SE) and astigmatic prediction error between subjective refraction (SUBref) and autorefraction (AUTOref) after cataract surgery to determine whether the latter is useful as an objective method to compare the accuracy of different methods of intraocular lens (IOL) power calculation.

METHODS

Postoperative refraction was examined using two techniques: SUBref and AUTOref. The results of these two techniques were compared. Predicted postoperative refraction for spherical outcome was calculated with the Barrett Universal II (BUII), Haigis, Holladay I, SRK/T, Hoffer Q, and BUII with measured posterior corneal astigmatism (MPCA) formulas. Predicted postoperative refraction for astigmatic outcome was calculated with the Barrett Toric calculator, vergence-based toric calculator using the Holladay 1 formula for effective lens position, and Barrett Toric calculator MPCA formulas. Formula accuracy and ranking were compared between the two methods of refraction.

RESULTS

Data were obtained from 219 eyes of 155 patients. Statistically significant differences were detected between SUBref and AUTOref for SE, J₀, and J₄₅ (P < .001). The spherical outcome formula analysis demonstrated no significant differences, whereas the predicted cylinder power analysis demonstrated significant differences within individual formulas between SUBref and AUTOref measures. The lowest median absolute error and the highest percentage of eyes achieving their refractive target for both SUBref and AUTOref were achieved with the BUII formula and the Barrett Toric calculator.

CONCLUSIONS

AUTOref is a useful method with adequate accuracy to determine spherical and astigmatic outcome and equally or more effective in being able to discriminate between spherical outcome formulas. The AUTOref method can allow valuable studies to be conducted in less-than-optimal environments and provides the ability to compare studies without the confounding factors of SUBref. [J Refract Surg. 2022;38(9):580-586.].

Measured Corneal Astigmatism Versus Pseudophakic Predicted Refractive Astigmatism in Cataract Surgery Candidates

PURPOSE

To compare standard and total corneal astigmatism measurements to the predicted pseudophakic (nontoric) refractive astigmatism in candidates for cataract surgery.

DESIGN

A retrospective, cross-sectional study.

METHODS

A single-center analysis of consecutive eyes measured with a swept-source optical coherence tomography biometer at a large tertiary medical center between February 2018 and June 2020. Corneal astigmatism was calculated based on standard keratometry astigmatism (KA), total corneal astigmatism (TCA), and predicted refractive astigmatism (PRA) for a monofocal nontoric intraocular lens (IOL) implantation calculated by the Barrett toric calculator using the predicted posterior corneal astigmatism (PRA_{(Predicted-PCA)}) and the measured posterior corneal astigmatism (PRA_{(Measured-PCA)}) options. Separate analyses were performed for each eye.

SETTING

Ophthalmology Department, Shaare Zedek Medical Center, Jerusalem, Israel.

RESULTS

In total, 8152 eyes of 5320 patients (4221 right eyes [OD] and 3931 left eyes [OS], mean age 70.6±12.2 years, 54.2% females) were included in the study. The mean vector values (centroid) for KA, TCA, PRA_{(Predicted-PCA)}, and PRA_{(Measured-PCA)} were 0.07 diopters [D] at 19.5°, 0.27 D at 7.5°, 0.44 D at 2.9°, and 0.43 D at 179.3°, respectively (P < .01), for OD and 0.02 D at 150.3°, 0.23 D at 169.7°, 0.40 D at 179.4°, and 0.42 D at 169.5°, respectively (P < .01), for OS. More than 73% of eyes had a PRA >0.5 D.

CONCLUSIONS

Standard and total corneal astigmatism measurements differ significantly from the PRA by the Barrett toric calculator. The PRA, rather than the KA or TCA, should be used as the reference guide for astigmatism correction with toric IOL implantation.

Using the first-eye prediction error in cataract surgery to refine the refractive outcome of the second eye

PURPOSE

To refine the refractive outcome of the second eye after cataract surgery by deriving adjustment coefficients for intraocular lens (IOL) selection based on the prediction error (PE) of the first eye.

SETTING

University Hospital Southampton, Southampton, England, and the Lions Eye Institute, Perth, Australia.

DESIGN

Retrospective study of two heterogeneous datasets.

METHODS

One hundred thirty-nine patients who underwent delayed sequential bilateral cataract surgery in Australia were retrospectively analyzed. The PE was determined by comparing postoperative subjective refraction with the predicted postoperative refraction (PPOR) calculated by the Barrett Universal II, Hoffer Q, Holladay I, and SRK/T formulas. Adjustment coefficients were derived for each formula and applied to the second eye's IOL calculation. Separately, patient-specific optimized IOL constants were derived from the first-eye PE and applied to the second-eye calculation. The same adjustments were applied to a dataset of 605 patients in the United Kingdom to test the validity of the Australian results.

RESULTS

The study comprised data on 139 patients in Australia and 605 patients in the U.K. The Australian-derived adjustment coefficients based on PE ranged from 0.30 to 0.56 (Barrett Universal II 0.30; Hoffer Q 0.56; Holladay I 0.53; SRK/T 0.48). Applying these to the U.K. dataset led to the percentage of patients within 0.50 diopters of PPOR with their second eye improving from 70.74%, 65.29%, 69.09%, and 67.77%, with the Barrett Universal II, Hoffer Q, Holladay I, and SRK/T, respectively, to 72.73%, 68.76%, 71.57%, and 72.56%. Using patient-specific optimized IOL constants derived from the first eye had similar efficacy to formula-specific adjustment.

CONCLUSION

Second-eye refinement via either formula-specific PPOR adjustment or patient-specific IOL constant adjustment improved the percentage of patients achieving the refractive target with their second eye.

Photodynamic Therapy with Verteporfin for Corneal Neovascularisation

Corneal neovascularization can be a difficult problem to treat. The authors describe a patient with lipid keratopathy secondary to corneal neovascularization treated with photodynamic therapy. Six months following treatment the neovascularization has not returned and the lipid keratopathy has not increased in size. No significant side effects from the treatment occurred. Photodynamic therapy with Verteporfin was a useful treatment modality in this case of corneal neovascularization with associated lipid keratopathy.

Postoperative endophthalmitis in a patient with Darier-White disease

CASE REPORT

We report a case of endophthalmitis after cataract surgery in a patient with Darier-White disease.

COMMENTS

A keratotic lid lesion in contact with the ocular surface near the temporal corneal wound is believed to be the source of infection. Such lesions are the predominant manifestation of Darier-White disease and are known to harbour gram-positive skin flora. This has implications for planning intraocular surgery in these patients.

Comparison of pseudophakic dysphotopsia with Akreos Adapt and SN60-AT intraocular lenses

PURPOSE

To determine the relative incidence of unwanted light images with the AcrySof SN60-AT intraocular lens (IOL) (Alcon) and the Akreos Adapt (Bausch & Lomb) IOL.

SETTING

The Eye Clinic, Sir Charles Gairdner Hospital, Nedlands, Australia.

METHODS

In a prospective randomized study of 61 patients who had cataract surgery, the relative incidence of unwanted light images with 2 biconvex acrylic double square-edged IOLs, the SN60-AT and Akreos Adapt, was compared. Patients were followed at 1 week and for a minimum of 6 weeks. At both follow-ups, patients were asked to rate their experience of dysphotopic phenomenon according to a set of questionnaire criteria. The Mann-Whitney test was used to analyze the ordinal data.

RESULTS

All 61 patients were interviewed at both stages of follow-up. The mean follow-up was 8 weeks +/- 2 (SD). At 1 week, there was significantly more dysphotopsia (positive and negative) with the SN60-AT IOL (37.5%) than with the Akreos Adapt IOL (24.1%) (P = .042). Significantly more patients with the SN60-AT IOL reported negative dysphotopsia at 1 week only. At 8 weeks, the incidence of positive and negative dysphotopsia declined to 31.3% and 20.7% in the SN60-AT group and Akreos Adapt group, respectively, and there was no longer a statistically significant difference between the 2 groups.

CONCLUSIONS

More patients with the SN60-AT IOL than with the Akreos Adapt IOL reported dysphotopsia. One week postoperatively, the difference was significant. The difference was primarily a result of the higher incidence of negative dysphotopsia with the SN60-AT IOL. At 8 weeks, the incidence of all types of light phenomena was significantly lower in both groups.

Prospective randomized controlled trial of the effect of intracameral vancomycin and gentamicin on macular retinal thickness and visual function following cataract surgery

PURPOSE

To investigate whether the use of vancomycin (20 microg/mL) and gentamicin (8 microg/mL) in the infusion fluid at the time of cataract surgery increases the incidence of macular thickening as measured with optical coherence tomography (OCT) following phacoemulsification.

SETTING

A public teaching hospital in Western Australia.

METHODS

Fourty-one patients (50 eyes) with cataracts between 50 and 85 years of age were randomized to receive no antibiotics in the infusion fluid at the time of cataract surgery (control group) or vancomycin (20 microg/mL) and gentamicin (8 microg/mL) in the infusion fluid (antibiotic group). Optical coherence tomography measurements were performed preoperatively and 1 day and 1 and 5 weeks postoperatively. A significant increase in macular thickness (mean of the central 1.0 mm diameter) on OCT was defined as 15 microm or greater. Five weeks postoperatively, the best corrected Snellen acuity and Pelli-Robson contrast sensitivity were measured.

RESULTS

Twenty-five percent in the control group and 38% in the antibiotic group had a significant increase in macular thickness measured on OCT 5 weeks postoperatively (P = .34). The mean contrast sensitivity of patients with increased macular thickness on OCT was 1.26, and in those with no change it was 1.43 (P = .001).

CONCLUSIONS

The use of intracameral vancomycin (20 microg/mL) and gentamicin (8 microg/mL) at the time of cataract surgery had no significant effect on macular thickness or visual function postoperatively. Overall, 31% of eyes showed an increase of 15 microm or greater in central retinal thickness. These patients had significantly reduced contrast sensitivity.

High-order aberrations in pseudophakia with different intraocular lenses

PURPOSE

To compare high-order aberrations in patients who had cataract surgery and implantation of different types of intraocular lenses (IOLs).

SETTING

Sir Charles Gairdner Hospital and Lions Eye Institute, University of Western Australia, Perth, Australia.

METHODS

Fifty eyes of 48 patients were included in this study. The optical aberrations were measured with the Hartmann-Shack wavefront sensor (Zyoptix, Bausch & Lomb) before and after surgery using a 5.0 mm wavefront aperture diameter for all comparisons. The eyes were divided into 4 groups according to the type of IOL (material and curvature). A fifth group of 10 eyes of 6 elderly patients with normal crystalline lenses had the same examination.

RESULTS

There was no statistical difference in high-order aberrations between the 2 acrylic IOL groups with different curvatures (P>.05) or between the silicone and poly(methyl methacrylate) (PMMA) IOL groups (P>.05). However, the measured high-order aberrations were significantly higher (3rd through 5th order) in the 2 acrylic IOL groups than in the PMMA and silicone IOL groups (P<.05).

CONCLUSIONS

An increase in IOL high-order aberrations contributed to the decline in retinal image quality. An IOL modifies the entire aberration pattern of the eye. There was a statistically significant increase in aberrations in patients with an acrylic IOL compared to those with a silicone or PMMA IOL. The exact mechanism is uncertain. Further study is required to optimize IOL design.

Coexistent adenoviral keratoconjunctivitis and Acanthamoeba keratitis

A 17-year-old youth presented with bilateral follicular conjunctivitis and nummular subepithelial corneal infiltrates. Failure of this to settle in an outpatient setting led to corneal scraping with microscopy and culturing for bacteria, fungi, Herpes simplex, adenovirus and Acanthamoeba as an inpatient. Polymerase chain reaction analysis of corneal cells was positive for adenovirus, and culture on live Escherichia coli-coated agar plates was positive for Acanthamoeba by phase contrast microscopy on day two. We conclude that Acanthomoeba infection can complicate adenoviral keratoconjunctivitis. This observation is in keeping with previously reported modes of infection by Acanthamoeba, whereby any epithelial breach seems to allow inoculation of the eye by this opportunistic organism.

In vitro bacterial adherence to hydrogel and poly(methyl methacrylate) intraocular lenses

PURPOSE

To compare the in vitro adherence of Staphylococcus epidermidis to poly-(hydroxyethyl methacrylate) (polyHEMA) or hydrogel intraocular lenses (IOLs) and poly(methyl methacrylate) (PMMA) IOLs.

SETTING

Lions Eye Institute, Perth, Western Australia.

METHODS

One-piece hydrogel lenses and one-piece PMMA lenses were suspended for 60 minutes in standardized suspensions of a well-characterized strain of S. epidermidis and then sonicated in a known quantity of balanced salt solution to remove the adherent bacteria. Quantitative cultures of the sonicates were performed and the results analyzed statistically.

RESULTS

The mean bacterial adherence of S. epidermidis to the PMMA IOLs (58,400 CFU) was more than 20 times greater than that to the hydrogel IOLs (1953 CFU). The difference was statistically significant (P < .001).

CONCLUSIONS

Adherence of S. epidermidis to hydrogel IOLs is significantly lower than to PMMA IOLs. This suggests that the risk of postoperative endophthalmitis after cataract extraction and IOL implantation may be lower with the use of hydrogel IOLs.

A new hydrogel intraocular lens design

A new hydrogel intraocular lens was designed to improve fixation and support. The lens, IOGEL model 2000S, has a 6.00 mm optic that merges via a crescentic flange into a terminal loop for an overall diameter of 12.00 mm. The haptics are more flexible than existing loops and the design of the lens is based on a concept of minimum loop rigidity; that is, a haptic that is rigid enough to support the weight of a lens in aqueous within the capsular bag is considered adequate for modern cataract surgery. I evaluated the lens design's safety and efficacy. Excluding patients with pre-existing macular degeneration, the corrected acuity of all patients at last follow-up was 20/40 or better in 100%, 20/30 or better in 95%, 20/25 to 20/20 or better in 85%, and 20/15 or better in 15%. The new haptic can accommodate compression of the capsular bag and allows early, reliable fixation. The centration of the lens was excellent early in the postoperative period and later after capsular fibrosis developed.

An improved universal theoretical formula for intraocular lens power prediction

Although available empirically derived and theoretical formulas perform adequately for eyes of average axial length, both have been shown to be deficient for eyes that have unusually short and long axial lengths. I developed a formula based on a theoretical model eye in which anterior chamber depth is related to axial length and keratometry. A relationship between the A-constant and a "lens factor" is also used to determine anterior chamber depth. The location of the intraocular lens' principle planes of refraction is retained as a relevant variable in the formula, and the user need not know the material and construction of the lens and or its constant. I compared the new formula with the SRK II, Holladay, and SRK/T formulas in a group of 100 unselected patients and in selected subgroups of patients with average, short, and long axial lengths. The new formula was significantly more accurate than the other third-generation formulas and maintained its accuracy in the subgroups. The formula can be described as universal because it can be used for different lens styles and for eyes with short, medium, and long axial lengths.

Pterygium excision with conjunctival autografting: an effective and safe technique

The optimum mode of treatment for symptomatic pterygia would combine efficacy (a low recurrence rate) with safety (freedom from sight threatening complications), and would not affect visual acuity adversely. The efficacy of pterygium excision with conjunctival autografting in a sun exposed population in which pterygia are prevalent has previously been questioned. A cross sectional review of 93 eyes of 85 patients was carried out by slit-lamp examination a minimum of 6 months (range 6-76 months) after pterygium excision and free conjunctival autografting. Case notes were reviewed to obtain details of complications and visual acuity changes related to surgery. Of six recurrences (6.5%) four of these were asymptomatic with minor recurrences. Two patterns of recurrence were identified: cross graft recurrence (three cases) and outflanking (three cases). Complications (wound dehiscence, three cases; Tenon's granuloma one case; conjunctival cyst, one case) were all corrected by minor surgical revision without sequelae. Unaided acuities were unchanged or improved 3 months after surgery in 86 cases, with a minor diminution (1 Snellen line) in seven cases. This study demonstrates a low recurrence rate for a safe technique in an area in which ongoing ultraviolet light exposure levels are high and pterygia are prevalent.

Combined small incision phacoemulsification and trabeculectomy

A method of combined cataract extraction and trabeculectomy is described in which phacoemulsification is performed through a 3.5 mm incision with insertion of a foldable hydrogel lens. This procedure is suitable for most cases in which glaucoma and cataract are coincident. In an initial series of ten patients followed for nine months, all those without additional pathology achieved a corrected visual acuity of 20/40 or better. The maximum induced astigmatism was 0.5 diopters (D), with no change or a reduction in astigmatism in seven patients (70%). Astigmatic shift between week 1 and three months was minimal (average = 0.075 D), with little change thereafter. Intraocular pressures were controlled (< or = 21 mm Hg) without adjunctive medication in all but one of the patients at nine months. This combined procedure preserves the principal advantages of small incision phacoemulsification: low induced astigmatism, early refractive stabilization, and rapid visual rehabilitation. In addition, reducing the extent of tissue dissection may reduce the stimulus to wound healing and early filtration failure.

Further studies on ultraviolet-absorbing hydrogels for intraocular lenses: relationship between concentration of a polymerizable benzophenone, absorption, and extractability

A tendency to reduce the use of benzophenone absorbers is currently evident in the manufacture of the UV-absorbing IOLs, mainly because the cutoff wavelengths are inferior to those provided by benzotriazoles. In principle, by incorporating large amounts of benzophenones it may be possible to achieve high cutoff wavelengths. A covalently bondable benzophenone UV absorber, Cyasorb UV-2098, was incorporated in poly(2-hydroxyethyl methacrylate) (PHEMA) in increasing concentrations, and certain associated phenomena were investigated. At 4% w/w absorber content, the nonhydrated polymers turned partially opaque. In water-swollen hydrogels, opacification occurred at a lower absorber content (2% w/w). By using extraction techniques and gas chromatography, we also found that up to 8% w/w of the absorber remained unpolymerized and could leach out from any material containing less than 5% w/w absorber. In samples with higher initial content of absorber, the amount of unreacted, leachable absorber was significantly higher (25% to 30%). Based on this study model (hydrogel/Cyasorb UV-2098), we concluded that benzophenone absorbers cannot provide cutoff wavelengths higher than those provided by benzotriazoles.

Cytotoxic effects of residual chemicals from polymeric biomaterials for artificial soft intraocular lenses

Development of improved hydrogels for soft intraocular lenses, based on 2-hydroxyethyl methacrylate monomer, requires the use of various other monomers and polymerization additives which have potential ocular toxicity. Three monomers, 2-hydroxyethyl methacrylate, methyl methacrylate, and 2-ethoxyethyl methacrylate, as well as two common inhibitors, hydroquinone and 4-methoxyphenol, were subjected to in vitro cytotoxicity assays as aqueous solutions at different concentrations. A new polymerization initiator, 2,2'-azo-bis-(2,4-dimethyl valeronitrile), was thermally decomposed in water at different concentrations and the products were also assayed for cytotoxicity. Assays were based on incubation with human choroidal fibroblasts. Cell death was evaluated by trypan blue dye exclusion, DNA synthesis inhibition, and lactate dehydrogenase tests. While methyl methacrylate and 2-ethoxyethyl methacrylate were found nontoxic, the other chemicals displayed high cytotoxicity. However, when extracts of synthesized poly(2-hydroxyethyl methacrylate) specimens, differentially treated after polymerization, were subjected to the same assays it was found that toxicity from residual 2-hydroxyethyl methacrylate monomer was lost during steam sterilization and storage in water because of the removal of the monomer through aqueous washing. The lack of toxicity in these specimens suggests that residual contents of inhibitor and initiator are too low to cause toxic effects on choroidal fibroblasts. It is concluded that hydrogels have low cytotoxic effects in vitro.

Laser-induced damage to transparent polymers: chemical effect of short-pulsed (Q-switched) Nd:YAG laser radiation on ophthalmic acrylic biomaterials. I. A review

The use of short-pulsed lasers in ophthalmic surgery inspired and called for research on the damage inflicted by the laser radiation upon the acrylic polymers from which artificial intraocular lenses are made. The possible release of toxic monomers by laser-induced depolymerization is of great concern but past investigations of this phenomenon have been very limited. The present knowledge of various types of laser-induced damage to transparent polymers is reviewed with particular emphasis on the acrylic materials and intraocular lenses.

Laser-induced damage to transparent polymers: chemical effect of short-pulsed (Q-switched) Nd:YAG laser radiation on ophthalmic acrylic biomaterials. II. Study of monomer release from artificial intraocular lenses

Commercial intraocular lenses and polymer specimens, both poly(methyl methacrylate) (PMMA) and poly(2-hydroxyethyl methacrylate) p(HEMA), were subjected to various levels of irradiation from a Q-switched Nd:YAG laser, and then to extraction and sample-enrichment techniques. The extracts were analysed by capillary gas chromatography. In PMMA samples, residual contents of 0.05-0.89% (wt) MMA were found and it appeared that the laser radiation did not cause a detectable increase of the monomer content. No residual HEMA could be found in p(HEMA) samples before or after laser bombardment. It is concluded that the accidental exposure of lenses to Nd:YAG laser cannot produce a significant release of monomers. Depolymerization induced by laser is a process unlikely to occur at the energy levels used in ophthalmic surgery.

Results of the intercapsular technique with the IOGEL lens

Standard biconvex 12 mm diameter IOGEL PC-1 hydrogel intraocular lenses were inserted into the eyes of 55 patients using intercapsular in-the-bag placement and extracapsular ciliary sulcus placement. All patients had senile cataracts. Endothelial specular microscopic assessment was performed preoperatively and postoperatively at six and 12 months. Viscoelastic agents were not used in any of the cases and upper haptic positioning was achieved with dialing and irrigation and iris retraction in each group, respectively. Major complications in both groups were iridocapsular synechias. This resulted in dislocation of a single haptic into the anterior chamber angle in one ciliary-sulcus-placed lens and in an updrawn pupil in one of the intercapsular cases. Pigment dispersion syndrome occurred in one case with a ciliary-sulcus-placed lens. In one case in each group a Nd:YAG laser posterior capsulotomy was performed. Whereas the visual results in each group were similar, the percentage cell loss was significantly greater in the group with lenses in the ciliary sulcus at six months postoperatively. The lower cell loss in the intercapsular group was attributed to the protective effect of the anterior capsule on the endothelium during the major intraocular manipulations.

Multicenter trial of an intraocular hydrogel lens implant

Several features suggest that hydrogels may have potential advantages as an intraocular lens material. The IOGEL lens is a single piece hydrogel composed of 38% poly HEMA. Clinical experience with the IOGEL lens in Australia has been published, and the safety and efficacy of the lens is currently being investigated in a multicenter trial in Europe, the U.S.A., Canada, Australia, and Japan. This is the first large-scale study of a hydrogel implant. The IOGEL lens clinical study was initiated in May 1986 in Europe, in September 1986 in the U.S.A., and in November 1986 in Canada and Australia. The enrollment progress in May 1987 showed that 501 cases had been implanted in Europe, Canada, and Australia and 100 cases in the U.S.A. The visual acuity outcome is equivalent to that reported in the literature. Patients in the multinational trial achieved 20/40 or better in 86% of cases and in 96% of cases excluding unrelated pathologies. Although hydrogels have only had limited use in the clinical situation, the results of this study suggest that the IOGEL lens is a viable alternative to polymethylmethacrylate lens implants.

Intraocular lens calculation formulas for new intraocular lens implants

Several different formulas are available for preoperative calculation of the required implant power for a desired postoperative refraction. However, the application of both theoretical and statistically derived regression formulas to the new generation of soft intraocular lens implants poses several difficulties. In this paper the calculation of an A constant for a specific intraocular hydrogel lens implant, as well as the derivation of a universal theoretical formula, is described. The theoretical formula can be applied to other implant styles with various optical configurations and composed of different biomaterials. The SRK and theoretical formulas have been applied retrospectively to a series of patients receiving an intraocular hydrogel lens implant. A comparison shows that both perform satisfactorily in predicting the desired postoperative refraction.

Clinical results of hydrogel lens implantation

Polymethylmethacrylate has proven to be a useful intraocular lens (IOL) implant material and remains the most widely used material for the fabrication of IOLs. Complications, however, from IOL implantation still occur. A hydrogel lens has been designed for posterior chamber placement. A clinical study from August 1983 to June 1985 was undertaken to determine the safety and efficacy of this new lens manufactured from 38% poly HEMA. The noninflammatory postoperative complications were limited to lens decentration and opacification of the lens capsule. Three cases of posterior capsule opacification required YAG laser capsulotomy. Laser capsulotomy is feasible and the lens appeared to be more resistant to damage from the YAG laser than polymethylmethacrylate lenses. In general, the material appeared to be well tolerated and there have been no cases of persistent iritis or clinically detectable cystoid macular edema. If the visual acuity outcome by age decade for all patients irrespective of follow-up time is considered, 92% of patients achieved 20/40 or better corrected visual acuity.

Antinociceptive effect of peripheral segmental electrical stimulation in the rat

We have investigated the effect of transcutaneous electrical stimulation, applied to the base of the tail, on the flexor withdrawal response of the rat, following immersion of the tail in water at 49 degrees C. In intact rats, electrical stimulation delayed the response to the controlled noxious stimulus, the delay depending on the duration of stimulation and on the frequency and pulse width of the stimulus. The prolongation in reaction time produced by stimulation at 100 Hz, 0.2 msec for 30 min at a voltage sufficient to cause slight fibrillation of the tail muscles, but no escape behaviour, was equal to that produced by 7.5 mg/kg of morphine. The specific narcotic antagonist naloxone (1 mg/kg) virtually abolished the effect of the electrical stimulation. After recovery from the operation, rats with complete spinal transection at the 10th or 11th thoracic vertebra exhibited a flexor withdrawal response to the noxious stimulus behaviourally simpler and of shorter latency than that exhibited by the intact animals. Peripheral electrical stimulation again delayed the response, and naloxone prevented the delay, but the antinociceptive action of the stimulation was quantitatively less than that observed in intact animals. Morphine also had a correspondingly reduced effect in the spinal animals. Depletion of 5-hydroxytryptamine levels by systemic pretreatment with parachlorphenylalanine significantly diminished the effect of both electrical stimulation and morphine administration in intact rats, but not in spinal rats. Our results support the concept that peripheral electrical stimulation excites naloxone-dependent antinociceptive mechanisms at both spinal and supraspinal levels. The supraspinal mechanism, but not the spinal mechanism, is associated with 5-hydroxytryptamine.

Failure of naloxone to reverse peripheral transcutaneous electro-analgesia in patients suffering from acute trauma

Transcutaneous electrical stimulation of the intercostal nerves innervating the site of fractured ribs in 6 patients produced subjective and clinical evidence of decrease in the pain experienced by the patients. This analgesia was not significantly modified by naloxone, a pure narcotic antagonist. The possible role of endogenous morphine-like substances in peripheral electro-analgesia in man is discussed.

Naloxone-reversible peripheral electroanalgesia in intact and spinal rats

Peripheral electrical stimulation of the rat produced a "dose-dependent" analgesia both in intact and in spinal animals. Naloxone, a narcotic antagonist, almost completely reversed this analgesia. It is felt that peripheral electroanalgesia acts via the release of endogenous narcotic-like substances, the enkephalins, at spinal and supraspinal centres.