Intraocular lens power calculation for lens exchange

PURPOSE

To examine patients who had intraocular lens (IOL) exchange for large postoperative refractive errors and determine the factors that contributed to the error in IOL power calculation.

SETTING

Thirteen affiliated hospitals in Japan.

METHODS

This study comprised 34 cases that required IOL exchange because of large refractive errors after primary lens implantation. Patients with intraoperative complications were excluded from the study. The potential contribution of axial length, corneal refractive power, IOL manufacturer, and IOL fixation to errors in the predicted power was examined retrospectively. Axial length was calculated by the SRK/T and Holladay formulas using refraction after primary IOL implantation.

RESULTS

There was no statistical difference between the corneal refractive power before and after cataract surgery. The axial lengths calculated using the SRK/T and Holladay formulas were longer than the ultrasonic axial lengths in 24 and 23 cases, respectively. Using IOLs from the same manufacturer for both primary implantation and exchange reduced the error in predicted refraction.

CONCLUSION

Axial length and IOL manufacturer were important factors in predicting refraction power in eyes requiring IOL exchange.

[Accuracy of intraocular power calculation formulas]

PURPOSE

We examined the accuracy of intraocular lens power calculation formulas, with special emphasis on the prediction of refraction in different axial lengths.

MATERIAL AND METHODS

786 cases were subdivided into four groups based on the axial length (short axial length < 22.0 mm, normal axial length = 22-24.4 mm, mid-range axial length = 24.5-26.9 mm and long axial length > 27 mm). Seven different formulas (Holladay, SRK, SRK II, SRK/T, S-SRK, M-SRK, L-SRK) were tested for their accuracy in predicting post-operative refraction.

RESULT

The best results were obtained using the S-SRK formula in the short axial length group (n = 114), The SRK and Holladay formulas in the normal axial length group (n = 278). The Holladay and SRK/T formulas in the mid-range axial length group (n = 135), and the SRK/T and L-SRK in the long axial length group (n = 259).

CONCLUSION

Our results emphasize the importance of using an intraocular lens formula specific for each range of axial length when calculating the predicted refraction.

[Vascular endothelial growth factor levels in the aqueous and serum in diabetic retinopathy with or without neovascular glaucoma]

We determined the levels of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) in the aqueous and serum in non-insulin dependent diabetic patients with proliferative retinopathy (n = 12) and neovascular glaucoma (n = 11). The aqueous levels of PEGF/VPF were significantly higher in both groups than in 10 diabetics without such complications. The levels were very high in patients with neovascular glaucoma, suggesting that VEGF/VPF is involved in the pathogenesis and progression of diabetic neovascular glaucoma. The serum levels were not significantly related to the presence or the stage of retinopathy. The findings suggest the possibility of treatment of neovascular glaucoma using anti- VRGF/VFP preparations.

Analysis of preoperative factors predictive of visual acuity in axial myopia

PURPOSE

To identify the factors predicting visual acuity after cataract surgery in patients with high myopia.

SETTING

Departments of Ophthalmology, Showa University School of Medicine and Showa University Fujigaoka Hospital, Kanagawa, Japan.

METHODS

Stepwise regression analysis was used to identify the factors determining the visual acuity in 940 eyes with an axial length of 27.0 mm or longer having cataract surgery. Using a formula derived from the stepwise regression analysis, the predicted postoperative visual acuity was compared with the actual value measured in another group of 104 eyes.

RESULTS

Five factors were identified to significantly determine postoperative visual acuity: axial length, age, corneal opacity, refractive power of the cornea, and history of retinal detachment surgery. There was a significant relationship between predicted and actual postoperative visual acuities (r = .51, P < .001). Postoperative visual acuity was similar in 63% of cases.

CONCLUSION

The results showed that at least five factors determine visual acuity after cataract surgery in patients with high myopia.

Fine structure of the tongue and lingual papillae of the penguin

The tongue in four species of penguin was investigated by light microscopy and by scanning electron microscopy, with special reference to the lingual papillae. 1) The middle of the penguin tongue contains a pair of long cartilages and long tendons accompanied by striated muscle bundles. 2) Large, spine-like, and caudally directed lingual papillae (filiform-like papillae) densely cover the dorsal surface of the tongue, apparently serving to catch fishes. 3) By light microscopy, the dorsal lingual epithelium with the lingual papillae are seen as a thick cornified layer, but the lateral and lower surfaces have a thinner cornified layer. 4) The connective tissue core (CTC) under the epithelium of the lingual papilla shows a stereo structure similar to but smaller than the external form of the papilla. The CTC contains some blood vessels and nerve fibers; the lingual glands are found in the submucous layer only in the posterior tongue. 5) Bundles of nerve fibers in the lamina propria of the tongue were immunohistochemically positive for PGP 9.5, and it appeared that Merkel corpuscles were distributed in the connective tissue closely beneath the epithelium of the finger-like papillae, though they were only weakly immunoreactive for PGP 9.5. 6) Numerous fine filaments of elastic fibers are found closely beneath the epithelial cell layer of the dorsal surface of the tongue including the lingual papillae, while there are very few of them on the lateral and lower sides of the tongue.

[Change in intraocular pressure after intraocular lens implant during a follow-up period of over 10 years]

Changes in intraocular pressure were studied in 141 eyes following intraocular lens implant. The average observational time was twelve years. We tried to fix both loops of the implant in the ciliary sulcus. The intraocular pressure increased over the ten year interval at 0.19 mmHg per year. Twenty-seven of the 141 eyes developed glaucoma. We studied the intraocular pressure of the cases with or without complications. Thirty-eight eyes had complications, fifteen eyes (39%) developed secondary glaucoma, and three eyes (8%) developed glaucomatous visual field defect. In twenty-three cases without secondary glaucoma, the intraocular pressure increased over a three-year interval after surgery and remained constant thereafter. 103 eyes had no complications to influence the intraocular pressure, twelve eyes (12%) developed secondary glaucoma, and four eyes (4%) developed glaucomatous visual field defect. In 91 cases without secondary glaucoma, the intraocular pressure increased over a five-year interval after surgery at 0.28 mmHg per year and remained constant thereafter. We recommend regular examination, especially during the initial five-year period when the intraocular pressure is apt to increase even if complications are not evident.

Intraocular lens power calculation for microphthalmos

PURPOSE

To evaluate the refractive results and accuracy of intraocular lens (IOL) power calculation formulas in eyes with microphthalmos.

SETTING

Department of Ophthalmology, Showa University Hospital, Tokyo, Japan.

METHODS

The accuracy of IOL power calculated using the SRK, SRK II, S-SRK, SRK/T, Holladay, and Hoffer Q formulas was evaluated in six eyes with axial lengths less than 19.0 mm.

RESULTS

Postoperative measurement of refraction showed a tendency toward hypermetropia compared with the refraction predicted by each formula. The best predicted refraction was calculated using the SRK/T formula. The tendency for hyperopic estimation was related to the axial length, particularly in eyes with a shorter axial length. However, there was no relationship between the refractive power of the cornea and the error in the predicted refraction by the SRK/T formula. Two eyes with an IOL power of 30.0 diopters (D) had severe hypermetropia.

CONCLUSION

Theoretical formulas were more accurate than empirical ones in eyes with microphthalmos. The severe hypermetropia in the two eyes with a 30.0 D IOL indicates that such patients require a higher IOL power.

[Pharmacokinetics of norfloxacin and lomefloxacin in aqueous humour analysed by microdialysis]

The pharmacokinetics of norfloxacin (NFLX) and lomefloxacin (LFLX) in rabbit aqueous humour after instillation of 0.3% solution (20 microliters) and oral administration (20 mg/kg) were investigated by microdialysis. We also measured plasma concentration of fluoroquinolones after oral administration. After instillation, the maximum concentration (Cmax) of NFLX and LFLX in the aqueous humour was 0.80 and 1.20 micrograms/ml, and elimination half time (t1/2) was 130 and 96 min, respectively. After oral administration, the Cmax in plasma of NFLX and LFLX was 2.06 and 1.89 micrograms/ml, and the Cmax in aqueous humour was 0.16 and 0.62 microgram/ml, respectively. t1/2 of NFLX in aqueous humour and plasma was 225 and 295 min, and t1/2 of LFLX was 188 and 175 min, respectively. The ratio of aqueous humour/serum concentration of NFLX and LFLX was 7.8 and 35.3% 4 hrs after oral administration. These results suggest that, after instillation, LFLX penetrated better into the aqueous humour, and was eliminated faster, than NFLX, and that after oral administration, NFLX could not panetrate well into the aqueous humor from the blood.

[Intraocular lens power calculation for short eye]

The accuracy of intraocular lens power calculation formulas for short eyes was examined. We examined 217 eyes with an axial length of shorter than 22.5 mm, with postoperative visual acuity of 0. 5 or more, and postoperative astigmatism of less than +/- 2D. Five formulas were tested for accuracy in prediction for postoperative refraction, the S-SRK, the SRK, the SRK II, the SRK/T, and the Binkhorst formulas. The best results were produced by the S-SRK formula which predicted 74% of the cases within +/- 1D error, if the axial length was shorter than 22 mm. The A-constant was also examined to study the effect of postoperative refraction. The A-constant takes into consideration the depth of the anterior chamber lens, so that the differences in depth would be influenced for short eyes rather than regular eyes in prediction. However, there was no significant difference among the different A-constant groups.

[A study of the intraorbital blood flow using ultrasound color Doppler mapping images in optic canal fracture cases]

Ultrasound color Doppler flow mapping image (CFMI) equipment, SSA-270A (Toshiba Co) was used to measure the blood flow velocity of the ophthalmic artery (OA) and the central retinal artery (CA) in eyes with optic canal fracture. The maximal blood flow velocity (V max), the minimal blood flow velocity (V min), the mean blood flow velocity (V mean), and the resistance index (RI) before and after transethmoidal decompression of the optic nerve were compared. The examination was conducted on 13 patients. There was no difference in blood flow velocity in the CA after the operation. Pre-operative V max and RI of the OA in the damaged eyes were lower than in normal eyes, but they increased the day after the operation. We measured the intraorbital blood flow velocity by CFMI because ultrasound does not penetrate bone. Since the peripheral artery from the optic foramen did not change after the operation, we concluded that the peripheral blood flow of OA had been quantitatively improved by the trans-ethmoidal decompression of the optic nerve.

[Central ocular hypotensive effect of noradrenaline]

We investigated the effects of topical and central administration of noradrenaline (NA) on the intraocular pressure (IOP) in pigmented rabbits. Unilateral instillation of NA (200 micrograms) produced no significant change in IOP. On the other hand, intracerebroventricular (ICV) administration of NA (0.01-1 micrograms) decreased IOP in both eyes in a dose-related fashion. The ocular hypotensive effect of NA was diminished by sympathectomy of the superior cervical sympathetic nerve or by ICV pretreatment with yohimbine hydrochloride 1-10 micrograms). These results suggest that the hypotensive effects of contrally administered NA might be mediated by alpha 2-adrenoceptor stimulation in the central nervous system.

[An intraocular lens power calculation for high myopia]

The accuracy of intraocular lens power calculation formulas for the axial high myopia were examined, especially regarding the point of the predictive refraction. We examined 170 eyes with axial lengths of 27 mm or longer, with postoperative visual acuity of 0.5 or more, and postoperative astigmatism of less than +/- 2D. Five formulas were tested for accuracy in predicting postoperative refraction. They were the L-SRK, SRK, SRK II, SRK/T, and Binkhorst formulas. The SRK formula tended to predict less myopia than the actual postoperative refraction. The SRK II and Binkhorst formulas predicted more myopia than the actual postoperative refraction. The best results were produced by the L-SRK and SRK/T formulas. The accuracy of the L-SRK formula predictions were measured for each of the four myopic levels. The same was done for the SRK/T formula. For both formulas, there was no statistically significant difference in accuracy of prediction for the four myopic categories. The two formulas are considered to be useful for high myopic cases.

[Application of microdialysis for pharmacokinetic study in rabbit anterior chamber]

We evaluated a microdialysis technique for analyzing the pharmacokinetics of instilled or orally administered ofloxacin in the anterior chamber of pigmented rabbits. A microdialysis probe was inserted into the anterior chamber and was perfused (2 microliters/min) with Ringer solution using a microinjection pump. Two hours later, 20 microliters of 0.15 and 0.3% ofloxacin was instilled into an eye, or 20 mg/kg of the drug was administered into the stomach through an intubated catheter. Dialysate was then collected every 15 or 20 min for 6 (instillation) or 8 (oral administration) hours. Ofloxacin concentration in dialysates was determined with a HPLC-spectrofluorometry system. Ofloxacin levels in dialysates increased after the instillation in a dose-related manner, reached a maximum at 30 and 45 min, and then decreased gradually with t1/2 of 136 and 114 min after the 0.15% and 0.3% instillation, respectively. After oral administration, ofloxacin levels in dialysates reached a maximum at 120 min and decreased with t1/2 of 175 min. These data suggest the usefulness of microdialysis for pharmacokinetic studies in the anterior chamber, since continuous and stable data can be obtained from each animal.

Preferred postoperative refraction after cataract surgery for high myopia

Eighty-four patients (121 eyes) with high myopia who had cataract surgery and intraocular lens implantation completed a survey on preferred postoperative refraction. Forty-two percent of the sample reported that they were accustomed to removing their glasses to read a newspaper or book. These respondents were fitted with soft contact lenses and their refraction changed to 0 D, -3.00 D, and -5.00 D. Of the patients whose best corrected postoperative visual acuity was 20/40 or better (n = 63), 48% preferred the -3.00 D correction; 38%, the 0 D correction; and 14%, -5.00 D. Of those with a best corrected postoperative visual acuity worse than 20/200 (n = 8), 80% preferred the -5.00 D refraction, which allowed them to read close up. Most patients with phakic eyes and good visual acuity (n = 13) preferred the 0 D and -3.00 D corrections. Our results indicate that in patients with high myopia, it is important to take patient preference into account when selecting postoperative refraction.

Eye growth after cataract extraction and intraocular lens implantation in children

We studied the effect of cataract extraction and intraocular lens (IOL) implantation (14 unilateral and 2 bilateral cases) on eye growth in 16 children. Visual acuity, refractive power, axial length, corneal curvature, and anterior chamber depth in both the operated and unoperated eyes were measured before and after surgery. The operated eyes tended to become myopic (maximum, -11.00 diopters). However, though the axial length of two eyes increased significantly after surgery, there was no significant difference between the postoperative increase in axial length in the operated and in the unoperated eyes. The anterior chambers of the unoperated eyes tended to be deeper. We suggest that the tendency to become myopic in the operated eyes occurred because, as axial length increases with growth, the proportion occupied by the vitreous body, ie, the part posterior to the IOL, also increases.

Long-term study of children with implanted intraocular lenses

We studied children between five and 15 years of age who were implanted with intraocular lenses (IOLs). The subjects comprised eight cases of traumatic cataract, 11 of congenital cataract, and six of steroid cataract. The follow-up ranged from four months to nine and one half years. Twenty of the eyes studied achieved a postoperative visual acuity of equal to or better than 20/40. Binocular function was retained in most cases. Postoperative complications included seven cases of posterior iris synechia, three of iris capture, one of transitory elevated intraocular pressure, and one of cystoid macular edema. Corneal endothelial studies were normal in the eyes in which posterior chamber IOLs were implanted.

[The role of sympathetic cervical ganglion in the effect of clonidine for lowering intraocular pressure]

The contribution of sympathetic cervical ganglion to the mechanism of action of clonidine for lowering intraocular pressure (IOP) was investigated. Pigmented rabbits were used. The animals were divided into 3 groups: normal control group (group 1), animals in which the bilateral cervical sympathetic trunks had been amputated presynaptically (group 2), animals in which the superior cervical ganglion (SCG) had been bilaterally dissected (group 3). Changes in IOP were measured after topical application of clonidine unilaterally. In group 1, IOP was significantly decreased in eye treated by clonidine and contralateral eyes compared to pretreatment values. Decrease of IOP in the contralateral eye was greater than that in the treated eye. In group 2, IOP was decreased in the contralateral eye but increased in the eye treated by clonidine. Pretreatment of yohimbine administered orally antagonized the ocular hypotensive effect of clonidine in a dose-related manner. In group 3, where SCGs were dissected, no changes in IOP were observed in both eyes by unilateral administration of clonidine. These results suggested that the bilateral ocular hypotensive effect of clonidine administered unilaterally is in part due to direct action on the SCG and that the alpha 2 receptor in the SCG plays some role in the regulation of IOP.

[Ocular hypotensive effect of alpha-adrenoceptor agonist and antagonist in the conscious pigmented rabbit]

It has been reported that some of the topically-used antiglaucomatics have a central ocular hypotensive effect. In this study, the influence of topical and intracerebroventricular (i.c.v.) administration of phenylephrine, clonidine, guanfacine, prazosin, yohimbine on the intraocular pressure (IOP) was investigated in the rabbit. Male pigmented rabbits were used throughout the experiments. For measurement of IOP, an applanation pneumatonograph was used. By unilateral topical administration of phenylephrine, an increase in IOP in the eye in which instillation was performed was observed. On the other hand, a slight decrease in IOP was observed by similar treatment of prazosin and yohimbine. No significant change of IOP in the contralateral eye was observed with these drugs. On the contrary, unilateral topical administration of clonidine or guanfacine decreased the IOP of both eyes. Furthermore, the decrease of IOP was more remarkable in the contralateral eye compared to the eye which received instillation. The IOP of both eyes was decreased in a dose-related fashion by i.c.v. administration of clonidine or guanfacine. The ocular hypotensive effects of clonidine were diminished by the pretreatment by i.c.v. administration with yohimbine. These results suggest that the ocular hypotensive effect of clonidine and guanfacine is due to their alpha 2-adrenoceptor stimulation in the central nervous system.

Errors in IOL power calculations for axial high myopia

We studied 115 eyes with axial lengths of 27 mm or more after implantation of a posterior chamber intraocular lens in order to determine discrepancies between the predicted refractions and the actual postoperative refractions. We then reviewed the three major variables used to predict refractions in these eyes--corneal curvature, anterior chamber depth, and axial length measurements--in an attempt to determine whether any of these variables were correlated with the discrepancies. We found that the main reason for postoperative refractive error was inaccurate measurements of preoperative axial length.

A simple modified SRK formula for severely myopic eyes

We describe our modification of the most accurate intraocular lens power calculation formula currently used, the SRK formula, to improve the accuracy with which it can be used to calculate the power of IOLs that are implanted in severely myopic eyes, especially in those with exceptional axial length. This modified formula, which we call the L-SRK, is I = A - 2.5 L - 0.9 K - 1.69R - 1.69 (where I = the actual implanted IOL power; A = the A-constant; L = the axial length; K = the average keratometer reading; and R = the predicted postoperative refraction). The results achieved using this modified formula demonstrate its superior accuracy in calculating lens powers for severely myopic eyes.

A new intraocular lens formula for high myopia

We developed a formula suitable for calculating intraocular lens power for eyes with axial lengths of 27 mm or greater. We then used this formula in a prospective study to determine its reliability in 32 eyes. In these latter cases the mean error between predictive postoperative refraction and actual postoperative refraction was 0.36 D, with 67% of the cases having less than 1.0 D error; 84% of the cases having less than a 2.0 D error; and no cases having an error greater than 3.0 D. The new formula provided greater accuracy for these highly myopic eyes than the SRK, SRKII, Hollady, and Thompson formulas.