Changes In Anterior Corneal Curvature Research Articles

Effect of timolol maleate (0.5%) in the management of myopic regression post laser-assisted in-situ keratomileusis: Clinical and topographical outcomes.

Purpose:The aim of this study was to analyze the effect of timolol maleate (0.5%) eye drops in the treatment of myopic regression after laser-assisted in-situ keratomileusis (LASIK).Methods:The study was conducted at a tertiary care eye hospital in north India between April 2017 & March 2018 as a prospective interventional study. Patients who underwent uneventful myopic LASIK with hansatome mechanical keratome and presented with regression were included in the study. Baseline demographic characteristics, time to presentation with regression best-corrected visual acuity (BCVA), refraction, intraocular pressure, central corneal thickness and keratometry were recorded at baseline and at each follow-up visit. The enrolled patients were prescribed timolol maleate (0.5%) eyedrops twice daily. They were followed up every month till 3 months on timolol maleate (0.5%) eyedrops and at 6 months post stopping the treatment.Results:Twenty-nine eyes of 15 patients were enrolled in the study. Mean pre LASIK spherical equivalent (SE) was – 7.48 ± 2.9 Diopters (Range-3.125 to –11.75 Diopters) and mean regression spherical equivalent was –1.02 ± 1.1 Diopters. There was a decrease in mean SE from presentation (intervention start point) up to 6 months follow-up (–1.34 ± 0.89 to –0.30 ± 0.29 Diopters). While posterior corneal curvature (K1 and K2 Back) changed significantly over treatment period (P = 0.0029, P = 0.0024 respectively), changes in anterior corneal curvature (K1 and K2 Front) were not significant (P = 0.05, P = 0.06 respectively). Central corneal thickness (CCT) and intraocular pressure (IOP) did not change significantly over treatment course.Conclusion:Timolol maleate (0.5%) eyedrop is an effective modality for the treatment of refractive regression post LASIK circumventing the need for laser re-treatment in such patients. The most probable mechanism is reversal of the anterior bowing of the cornea in response to intraocular pressure changes.

Corneal Tomography Changes and Refractive Outcomes After Descemet Stripping Without Endothelial Keratoplasty.

To investigate corneal tomography changes and refractive outcomes after Descemetorhexis without endothelial keratoplasty (DWEK). Retrospective chart review of 25 eyes from 16 patients with Fuchs corneal endothelial dystrophy that underwent successful DWEK combined with cataract surgery. There was no significant change in anterior corneal curvature on tomography maps. However, all tomography maps demonstrated an increase in central posterior float and all but one demonstrated a decrease in pachymetry after DWEK. Only 7 of 25 eyes had increased irregular astigmatism on tomography after DWEK, of which 57% had preexisting irregular astigmatism before the procedure. The mean difference between the targeted and outcome refraction was +0.65 diopters (D) at the time of corneal clearance, but this improved to +0.38 D 1 month after corneal clearance. Postoperative refraction was within 1 D of target refraction for 92% of cases (23 eyes) but within 0.5 D of target refraction for only 48% of cases (12 eyes). The differences between expected and actual refractive outcomes were correlated with change in posterior corneal curvature and pachymetry. DWEK induces an increased central posterior float localized to the site of Descemet membrane stripping, confirming the need for centralized stripping. Irregular astigmatism can occur after DWEK but is typically minimal and occurs more commonly in the setting of preoperative irregular astigmatism. DWEK induces about a 0.5 D hyperopic shift, which should be considered when determining intraocular lens power with simultaneous surgery.

Two-Year Refractive Outcomes After Descemet Membrane Endothelial Keratoplasty.

To monitor refractive changes after Descemet membrane endothelial keratoplasty (DMEK) and to determine what may influence these changes and the time point of stabilization. From 67 pseudophakic DMEK eyes operated on for Fuchs endothelial dystrophy at a tertiary referral center, biomicroscopy, visual acuity, subjective refraction, and Scheimpflug-based corneal tomography data were obtained before and up to 2 years postoperatively. Visual acuity and changes in spherical equivalent (SE), mean anterior and posterior simulated keratometry (Km), and central pachymetry were analyzed. At 3 months postoperatively, both hyperopic (28/67 eyes) and myopic (21/67 eyes) shifts were observed; 18/67 eyes showed no SE change. The mean change in SE at 3 months was +0.33 diopters (D) (95% confidence interval = [0.11, 0.54], P = 0.028), which stabilized thereafter (P > 0.466). Initial flattening of mean anterior Km by 0.66D (95% confidence interval = [-0.81, -0.51], P < 0.001) at 3 months was followed by a slow steepening, which became significant between 1 and 2 years postoperatively (P < 0.001). Posterior Km stabilized after 3 months (P > 0.252). Preoperative to 3 months postoperative absolute changes in anterior Km were positively related to preoperative backscattered light from the central anterior cornea (P = 0.035), and the presence of partial graft detachment postoperatively (P = 0.013). After DMEK, SE and posterior corneal curvature were on average stable at 3 months after surgery, whereas the mean anterior corneal curvature showed an ongoing gradual change. Changes in anterior corneal curvature may be related to preoperative anterior corneal densitometry or postoperative partial graft detachment.

Assessing the accuracy of Orbscan II post‐LASIK: apparent keratectasia is paradoxically associated with anterior chamber depth reduction in successful procedures

To establish a relationship between the forward protrusion of the cornea (keratectasia), following successful LASIK, and anterior chamber depth. One hundred and fifteen eyes of 59 patients who had undergone Zyoptix LASIK and 39 eyes of 21 patients who had undergone PlanoScan LASIK at the Eye Institute, Centre for Refractive Surgery, Remuera, Auckland, New Zealand, were included in the study. The results of Orbscan II acquisitions, taken before and 8.3 weeks +/- 4.0 (mean +/- standard deviation) following the procedure, were analysed to determine the amount of forward protrusion of the central 2 mm diameter of the posterior surface. The apparent keratectasia was then related to the Orbscan II anterior chamber depth (ACD) measurement in a linear mixed model analysis that included 'right or left eye', 'sex', 'type of LASIK procedure', 'change in pachymetry', 'postoperative pachymetry', 'change in anterior corneal curvature', 'postoperative anterior corneal curvature', 'planned ablation depth' and 'time until follow-up' as factors and covariates. The mean +/- SD amount of keratectasia determined by Orbscan II was 22.8 +/- 26.8 microm for the Zyoptix group and 16.9 +/- 24.6 microm for the PlanoScan group. The reduction in depth of the anterior chamber was 14.7 +/- 79.3 microm for the Zyoptix group and 18.2 +/- 68.8 microm for the PlanoScan group. The mixed model analysis demonstrated strong relationships with postoperative pachymetry and change in anterior corneal curvature (P < 0.001 and P < 0.001, respectively). Furthermore, the statistical model showed a marked significant difference in the Orbscan II assessment of keratectasia and change in ACD (P < 0.001). Using the Orbscan II device, the forward protrusion of the posterior corneal surface appears to coincide with a paradoxical reduction in depth of the anterior chamber. Although the keratectasia found in this study is accompanied by thin postoperative corneas and larger central pachymetry change, the contradictory decrease in anterior chamber depth creates uncertainty of measurement, and of ectasia as a mechanism of regression.

A laboratory model for microkeratome-assisted posterior lamellar keratoplasty utilizing a running graft suture and a sutureless hinged flap.

To evaluate changes in anterior corneal curvature and graft stability with different sized donor buttons in a laboratory model of posterior lamellar keratoplasty. Thirty-six human eye bank corneas (18 donors and 18 recipients) were mounted on an artificial anterior chamber. A manual microkeratome was used to create a hinged anterior lamellar keratectomy. A 7.0-mm diameter posterior lamellar disk (posterior stroma, Descemet's membrane, and endothelium) was then trephinated from the recipient cornea. Three different sizes (7.0, 7.25, and 7.5 mm) of donor buttons were compared. They were sutured into the recipient bed with a running 10-0 nylon suture and covered by the host corneal flap. The flap was replaced without sutures. The resulting endokeratoplasty was analyzed by computerized videokeratography and tonometry. Regular postoperative astigmatism was present in all cases. There was an average increase in astigmatism of 1.47 +/- 1.49 diopters (D) postoperatively. The mean change in the average keratometry readings was -5.12 +/- 6.12 D. The grafts and flaps maintained watertight seals with average leak pressures of 66.9 +/- 46.4 mm Hg. Although donor buttons oversized by 0.5 mm had the least change in average keratometry reading, those oversized by 0.25 mm had the best stability at high pressure. All groups had little change in astigmatism. The optimal sized button of those tested would be either oversized by 0.25 or 0.5 mm. This new surgical technique may result in lower risk of high and irregular astigmatism in the management of corneal endothelial disorders.

Excimer laser photorefractive keratectomy

Excimer laser photorefractive keratectomy has been used for the correction of myopia, hyperopia and astigmatism. This laser removes tissue through a process termed photoablative decomposition, in which incident photon energy is sufficient to break molecular bonds. Selective removal of tissue across the anterior corneal surface results in a change in anterior corneal curvature. The surgical outcome may be influenced also by interindividual variability in wound healing and pharmacologic interventions. The nature of the excimer laser-tissue interaction, and clinical outcomes of predictability, stability and complications of surgery for myopia are discussed in detail.

Topographic analysis of early changes in corneal astigmatism after cataract surgery

Using the Topographic Modeling System (TMS), we studied the early changes in anterior corneal curvature following cataract surgery. Thirty patients who had planned extracapsular cataract extraction (p-ECCE) or phacoemulsification were evaluated with TMS at three days, and one, two, three, and five weeks postoperatively. After p-ECCE, the upper part of the cornea which corresponded to the wound and the lower cornea markedly steepened and showed a bow-tie pattern of astigmatism. Eight (57%) of 14 cases showed little reduction in the corneal steepening at five weeks postoperatively. In five cases (36%) the steepening in the lower cornea was less than the minimal change in the upper cornea. After phacoemulsification, corneal steepening was much less than it was after p-ECCE; three cases (17%) showed almost no surgically induced alteration of the cornea. In eight phacoemulsification cases (61 %), postoperative corneal steepening decreased rapidly and the corneal shape recovered within five weeks. Our topographic analysis clearly demonstrated that a smaller wound in phacoemulsification surgery produced less corneal steepening and stabilized more rapidly than a larger wound in p-ECCE.

BETA‐ADRENERGIC RECEPTOR ANTAGONISM IN MYOPIA*

A previous study has demonstrated that timolol maleate (0.5%), a non-selective beta-adrenergic antagonist, produces in emmetropes a significant reduction in accommodative convergence (AC) during the initial four minutes of a near-vision task. The present study has examined the effect of timolol on AC for three refractive groups (each comprising N = 20): emmetropes, early-onset myopes (EOMs), i.e. myopia onset prior to 15 years of age and late-onset myopes (LOMs), i.e. myopia onset after 15 years. A double-blind protocol was adopted between timolol and a saline control. AC was derived from accommodation stimuli of 3.3, 4.1 and 4.8 D with changes in heterophoria being assessed using a Maddox rod and tangent scale. The relationship between the ocular hypotensive effect of timolol and anterior corneal curvature was also investigated using a Goldmann applanation tonometer and a two-position keratometer (Haag-Streit). Timolol produced a significant reduction in AC in emmetropes but did not induce significant changes in AC in LOMs or EOMs. The timolol-induced reduction in IOP did not result in any changes in anterior corneal curvature.