Corneal power measurements with the Pentacam Scheimpflug camera after myopic excimer laser surgery.

PURPOSE: To evaluate corneal power measurements by a rotating Scheimpflug camera (Pentacam, Oculus) in eyes that have had myopic excimer laser surgery. SETTING: Private practice, Bologna, Italy. METHODS: This prospective comparative interventional case series comprised 16 eyes of 16 patients who had myopic excimer laser surgery and for whom all perioperative data were available. Four corneal power measurements obtained with the Pentacam (simulated keratometry, true net power, equivalent K reading, and BESSt formula) were analyzed and compared with values derived using the clinical history method and 2 other formulas for calculating corneal power after refractive surgery (modified keratometric refractive index according to Savini et al. and separate consideration of the anterior and posterior corneal curvatures according to Speicher). RESULTS: Analysis of variance showed a statistically significant difference between all methods (P<.0001). Bonferroni multiple comparison tests showed that the only Pentacam measurements not statistically different from the corneal power values derived using the clinical history method were the equivalent K readings at 1.0 mm, 2.0 mm, and 3.0 mm and those derived with the BESSt formula; however, considerably large 95% limits of agreement (LoA) were calculated between each of these values and those obtained with the clinical history method. CONCLUSIONS: The Pentacam device gave corneal power measurements that did not statistically significantly had differ from those predicted by the clinical history method in eyes that had previous myopic excimer laser surgery. Wide LoA are a potential source of error in intraocular lens power calculation in such patients.

The effect of scan diameter on retinal nerve fiber layer thickness measurement using stratus optic coherence tomography.

OBJECTIVE: To study how customizing the peripapillary scan diameter on the basis of optic nerve head (ONH) diameter affects retinal nerve fiber layer (RNFL) thickness measurements using Stratus optical coherence tomography (OCT). METHODS: Retinal nerve fiber layer was examined using 1 fixed-diameter circular scan (3.4 mm) and 2 customized-diameter scans (at 0.5 mm and 1 mm from the ONH edge) in 81 healthy subjects. RESULTS: Using fixed-diameter scans, the mean RNFL thickness increased with larger ONH vertical diameters (r = 0.3425, P =.002), whereas using customized-diameter scans, negative correlations were detected (r = -0.3004 [P =.006] at 0.5 mm and r = -0.2369 [P =.03] at 1 mm from the ONH edge). The mean values obtained by customized-diameter scans showed lower standard deviations in most measurements, meaning a tendency toward lower interindividual variability. CONCLUSIONS: When RNFL thickness is measured at a constant distance from the ONH edge, larger discs exhibit a thinner RNFL. Hence, the correlation between large discs and thicker RNFLs observed using the standard fixed-diameter scan probably represents a technical artifact reflecting the shorter distance between the scan and the ONH edge. A new normative database, stratified not only on the basis of age but also on the basis of ONH size, is suggested.

Correlation between attempted correction and keratometric refractive index of the cornea after myopic excimer laser surgery.

PURPOSE: Given that the standard keratometric refractive index of 1.3375 is no longer valid after excimer laser surgery, we aimed to investigate how this value changes postoperatively and if any correlation to the attempted correction exists. METHODS: The pre- and postoperative data of 98 patients who underwent either myopic photorefractive keratectomy (PRK) or LASIK were reviewed. Using postoperative videokeratography, the corneal radius (r) was obtained; the corrected corneal power (Pc) was measured by separately calculating the dioptric power of the anterior and posterior corneal surfaces. The postoperative index of refraction (n(post)) was derived from these values using the formula: n(post) = (rPc) +1. RESULTS: As the amount of refractive change increases, n(post) progressively decreases (P < .0001, r = 0.9581). Linear regression provided the subsequent formula to calculate the postoperative index of refraction: n(post) = 1.338 + 0.0009856 x attempted correction. CONCLUSIONS: Myopic PRK and LASIK induce a decrease in the keratometric refractive index. This reduction correlates to the amount of attempted correction. When the latter is known, calculating n(post) may enable the measurement of corneal power and thus provide an additional method for calculating intraocular lens power in eyes that have undergone myopic PRK or LASIK.

Intraocular lens power calculation after myopic refractive surgery: theoretical comparison of different methods.

OBJECTIVE: To evaluate the reliability of different methods developed to calculate intraocular lens (IOL) power after corneal refractive surgery. DESIGN: Retrospective observational case series. PARTICIPANTS: Preoperative and postoperative data of all eyes that underwent myopic excimer laser surgery in a private practice (Centro Salus, Bologna, Italy) between 1999 and 2004 were reviewed. INTERVENTION: The following methods were analyzed: videokeratography, clinical history, Shammas' refraction-derived and clinically derived methods, Rosa's correcting factor, Ferrara's variable refractive index, separate consideration of anterior and posterior corneal curvature (with and without preoperative data), Feiz-Mannis' formula and nomogram, and Latkany's regression formulas (based on both average and flattest postrefractive surgery keratometry). The Holladay 1 formula was used for eyes with an axial length between 22 and 24.49 mm and the SRK-T for eyes longer than 24.49 mm. Double-K formulas were also evaluated, when applicable. Each IOL power determined with these methods was compared to a benchmark value, calculated using the preoperative axial length and corneal power and aiming for the preoperative spherical equivalent. MAIN OUTCOME MEASURE: Mean error in IOL power prediction. RESULTS: Ninety-eight eyes of 98 patients were analyzed. The double-K clinical history method, Feiz-Mannis' formula, double-K method based on separate consideration of anterior and posterior corneal curvature (with and without preoperative data), and both Latkany's regression formulas were the only methods resulting in a mean IOL power not statistically different (P>0.05) from the benchmark used for comparative purposes. CONCLUSIONS: When prerefractive surgery data are available, IOL power should be calculated using the double-K clinical history method. Alternative choices may be represented by the Feiz-Mannis' formula, Latkany's regression formulas based on average and flattest postrefractive surgery keratometry, and the double-K method based on separate consideration of anterior and posterior corneal curvatures. A variant of the latter can be used to calculate IOL power when prerefractive surgery data are not available. Further prospective studies based on patients undergoing phacoemulsification after refractive surgery are needed to validate the results of this theoretical comparison.

Detection and quantification of retinal nerve fiber layer thickness in optic disc edema using stratus OCT.

OBJECTIVE: To investigate the ability of optical coherence tomography (OCT) to assess changes in retinal nerve fiber layer (RNFL) thickness in optic disc edema. METHODS: Prospective observational case series in a private eye clinic (Centro Salus). Twelve consecutive eyes (9 patients) with optic disc edema were analyzed, including 6 patients with anterior ischemic optic neuropathy, 1 patient with multiple sclerosis-associated papillitis, and 2 patients with bilateral papilledema. Peripapillary scans of the RNFL were obtained using Stratus OCT (software version 3.0; Carl Zeiss Meditec, Dublin, Calif). Repeated measurements were performed in 7 patients during a follow-up ranging from 8 to 30 weeks. The main outcome was RNFL thickness measurement. RESULTS: Optical coherence tomography detected and quantified diffuse thickening of the RNFL. Compared with eyes in a control group of 75 healthy subjects, eyes with optic disc edema showed a significant increase in the mean RNFL thickness in all quadrants (temporal, P = .002; superior, P<.001; nasal, P<.001; and inferior, P<.001). In patients who were followed up, progressive thinning was observed as the disease evolved toward optic atrophy or clinical resolution. CONCLUSIONS: Optical coherence tomography can identify and measure RNFL edema. This ability of OCT may help elucidate pathophysiological mechanisms in optic disc edema and provide a valuable aid to clinicians.

Corneal melting associated with topical diclofenac use after laser-assisted subepithelial keratectomy.

We report a case of corneal melting associated with topically applied preservative-free diclofenac (Voltaren Ofta) after laser-assisted subepithelial keratectomy. Keratolysis was detected on day 5; further progression toward perforation was arrested by immediate suspension of diclofenac and prescription of topical dexamethasone with 24-hour patching. At the last follow-up, the visual acuity had improved from counting fingers to 20/20. Preservative-free diclofenac instillation had never been associated with keratolysis. Topical steroids may be useful in treating corneal melting associated with nonsteroidal antiinflammatory drugs.

Influence of pupil size and cataract on retinal nerve fiber layer thickness measurements by Stratus OCT.

AIM: To investigate whether retinal nerve fiber layer (RNFL) thickness, as measured by optical coherence tomography (OCT), is influenced by pupil size and cataract. METHODS: RNFL thickness was measured by means of Stratus OCT (RNFL Thickness 3.4 acquisition protocol) in a group of consecutive patients undergoing phacoemulsification and intraocular lens implantation. Measurements were taken preoperatively without pupil dilation (PR1), preoperatively with pupil dilation (PR2), and 1 month postoperatively without pupil dilation. RESULTS: Twenty-five eyes of 25 patients were enrolled in the study and underwent statistical analysis. Pupil dilation caused RNFL thickness measurements to increase slightly in PR2 compared with PR1; the difference showed to be statistically significant in the 360-degree average measurement (P=0.0456) and in the nasal quadrant (P=0.032), but not in the remaining quadrants. Postoperative measurements were higher than those of PR1 in all quadrants (temporal P=0.011; superior P=0.0098; nasal P<0.0001; inferior P=0.0081) and in 360 degrees average (P<0.0001), suggesting that the presence of cataract significantly influences RNFL thickness as measured by Stratus OCT. More advanced degrees of lens opacity were correlated to a higher decrease in RNFL thickness values (r=0.4071, P=0.0434). CONCLUSIONS: While pupil size only marginally affects RNFL measurements performed by Stratus OCT, the presence and degree of cataract seem to have a significant impact. This effect should be taken in consideration when using this technology for the diagnosis of glaucoma and other neuro-ophthalmologic disorders possibly affecting the RNFL.

Tear meniscus evaluation by optical coherence tomography.

BACKGROUND AND OBJECTIVE: To assess the ability of optical coherence tomography to visualize the inferior tear meniscus and measure its height. PATIENTS AND METHODS: Twenty-seven eyes (27 patients) with aqueous tear deficiency were compared with 20 eyes (20 patients) with normal tear secretion (control group). After the instrument was focused on the ocular surface, a 4-mm long vertical scan, centered on the lower tear meniscus at corneal 6 o'clock hours, was obtained using optical coherence tomography. Tear meniscus height was measured by means of an external application. RESULTS: Mean tear meniscus height was significantly lower (P < .0001) in patients with aqueous tear deficiency (mean +/- standard deviation: 0.13 +/- 0.07 mm) than in the control group (mean +/- standard deviation: 0.25 +/- 0.08 mm). CONCLUSION: Optical coherence tomography can be used to noninvasively visualize the inferior tear meniscus. This method seems able to discriminate between patients with normal and dry eyes when measuring tear meniscus height.

Retinal nerve fiber layer evaluation by optical coherence tomography in unaffected carriers with Leber's hereditary optic neuropathy mutations.

PURPOSE: To study retinal nerve fiber layer (RNFL) thickness by optical coherence tomography (OCT) in unaffected carriers with Leber's hereditary optic neuropathy (LHON) mutations. DESIGN: Cross-sectional study. PARTICIPANTS: Sixty-six unaffected carriers (44 females and 22 males) were analyzed and compared with an age-matched control group of 70 patients (40 females and 30 males). The statistical analysis was performed after grouping both the patients and the control group on the basis of gender and, for unaffected carriers only, mitochondrial DNA mutation. METHODS: The Fast RNFL Thickness (3.4) scan acquisition protocol was used. MAIN OUTCOME MEASURE: Retinal nerve fiber layer thickness as measured by OCT. RESULTS: With respect to the control group, unaffected male carriers showed a thicker RNFL in the temporal and inferior quadrants and in the 360 degrees average measurement (P = 0.025, P = 0.03, and P = 0.018, respectively). These differences reached statistical significance in subjects carrying the 11778 mutation, whereas only a trend was detected in those with the 3460 mutation. Unaffected female carriers had an increased thickness in the temporal quadrant when compared with the control group (P = 0.003) and no differences in the other measurements. The increase in temporal sectors was statistically significant in females with the 11778 mutation, whereas a trend was detected in those with the 3460 mutation. CONCLUSIONS: A thickening of the temporal fibers was detected in all subgroups of unaffected carriers. This is the first evidence indicating the preferential involvement of the papillomacular bundle in subclinical LHON. This notion previously was based on the early loss of fibers from the temporal quadrant in acute LHON and the selective loss of small-caliber fibers at histopathology. Our study also revealed that males have a more diffuse involvement than females.

Retinal nerve fiber layer evaluation by optical coherence tomography in Leber's hereditary optic neuropathy.

PURPOSE: To study retinal nerve fiber layer (RNFL) thickness by optical coherence tomography (StratusOCT) in patients with Leber's hereditary optic neuropathy (LHON). DESIGN: Cross-sectional study. PARTICIPANTS AND/OR CONTROLS: Thirty-eight patients with LHON were analyzed and compared with an age-matched control group of 75 patients. Patients with LHON were classified as having early LHON (E-LHON, n = 8) when the duration of the disease was shorter than 6 months and atrophic LHON (A-LHON, n = 30) when the duration was longer than 6 months. METHODS: The fast RNFL thickness (3.4) scan acquisition protocol was used. MAIN OUTCOME MEASURE: Retinal nerve fiber layer thickness as measured by StratusOCT. RESULTS: Compared with the control group, eyes with E-LHON showed a thicker RNFL in the 360 degrees average measurement (P<0.01) and in the superior (P<0.01), nasal (P<0.05), and inferior quadrants (P<0.05); no significant changes were detected in the temporal quadrant. Eyes with A-LHON revealed a thinner RNFL in all measurements (P<0.001); the fibers of the nasal quadrant showed the lowest amount of reduction (38% vs. 42%-49.8% in the other quadrants). In cases with A-LHON and visual recovery, RNFL was significantly thicker in all measurements (P<0.001), except the temporal quadrant, with respect to A-LHON without visual recovery. CONCLUSIONS: On the basis of OCT data, the RNFL is thickened in E-LHON and severely thinned in A-LHON. RNFL is likely to be partially preserved in A-LHON with visual recovery. The temporal fibers (papillomacular bundle) are the first and most severely affected; the nasal fibers seem to be partially spared in the late stage of the disease.

Ocular surface changes in laser in situ keratomileusis-induced neurotrophic epitheliopathy.

PURPOSE: To evaluate the ocular surface changes in patients with laser in situ keratomileusis (LASIK)-induced neurotrophic epitheliopathy. METHODS: Seven consecutive patients with LASIK-induced neurotrophic epitheliopathy were studied prospectively and compared to a control group (seven consecutive patients who had LASIK- but without neurotrophic epitheliopathy). Bilateral sequential LASIK was performed at a 1-week interval; the first operated eye of each patient was considered for statistical analysis. Blinking, corneal sensitivity, tear break-up time, tear secretion and clearance were measured preoperatively (T0) and postoperatively at 1 week after surgery on the first eye (T1), and 1 week (T2), 1 month (T3), and 3 months (T4) after surgery was performed on the second eye. RESULTS: Laser in situ keratomileusis-induced neurotrophic epitheliopathy occurred bilaterally in all patients. During follow-up, patients with LASIK-induced neurotrophic epitheliopathy showed a significant decrease in blinking (P = .0002), which was not observed in cases without LASIK-induced neurotrophic epitheliopathy [corrected] Compared to eyes without LASIK-induced neurotrophic epitheliopathy, those with LASIK-induced neurotrophic epitheliopathy revealed lower values of sensitivity in the central cornea preoperatively and early postoperatively (T0, P = .004; T1, P = .003; T2, P = .003). A trend towards reduced sensitivity was also detected in the central cornea in late follow-up and in the superior, temporal, and nasal sectors of the flap at all examinations. No significant differences were observed in break-up time, tear secretion, or clearance within or between the two groups. CONCLUSION: Decreased blinking seems to be involved in the pathogenesis of LASIK-induced neurotrophic epitheliopathy. The reduction probably depends on the lower levels of corneal sensitivity and induces the epitheliopathy by increasing the ocular surface exposure.

Peripapillary detachment in pathologic myopia: Unusual OCT findings.

PURPOSE: To report an unusual case of myopic peripapillary retinal detachment (PPRD) imaged by optical coherence tomography (OCT). METHODS: Observational case report. RESULTS: OCT showed a nonreflective space between the retinal pigment epithelium and the neurosensory retina with the presence of bridging tissue that could be defined as an outer retinal schisis, which is not typical of myopic PPRD. CONCLUSION: This case suggests that the spectrum of PPRD in pathological myopia may extend beyond that already described.

Filtering blebs imaging by optical coherence tomography.

PURPOSE: To assess the ability of standard optical coherence tomography to visualize filtering blebs after glaucoma surgery. METHODS: A prospective interventional case series was conducted in a private practice. Twenty-nine eyes of 24 patients (21 with good, 2 with fair and 6 with poor intraocular pressure [IOP] control) were investigated. After the focus was manually adjusted on the conjunctiva, blebs were scanned perpendicularly to the limbus. RESULTS: Hyporeflective fluid-filled spaces were detected in 19 out of the 21 eyes with good IOP. Within this group, blebs were classified into three different categories according to their optical coherence tomography pattern: type A (featuring a thick wall and a single large fluid-filled space), type B (featuring a thin wall and multiple large fluid-filled spaces) and type C (featuring multiple, irregular and flattened fluid-filled spaces). Fluid-filled spaces were not observed in three out of the six eyes with poor IOP control. Trabeculectomy without antimetabolites was associated with type A blebs (P = 0.015, Fisher's exact test), mitomycin-C trabeculectomy with type B blebs (P = 0.0025) and mitomycin-C phacotrabeculectomy with type C blebs (P = 0.0173). CONCLUSIONS: Although it was not developed to evaluate the anterior segment of the eye, standard optical coherence tomography can visualize filtering blebs and reveal interesting details of their morphology. Clinicians using optical coherence tomography to diagnose glaucoma can take advantage of this ability of the instrument to obtain more information about their patients in the postoperative course of trabeculectomy and phacotrabeculectomy.

Ocular findings in mitochondrial neurogastrointestinal encephalomyopathy: a case report.

PURPOSE: To describe the ocular features of a patient with mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) due to a homozygous G1443A mutation in the thymidine-phosphorylase gene. METHODS: A case report with extensive ophthalmological investigation over a 9-year period, until death at age 38 years. Measures used included standard ophthalmological examination, visual field examination and optical coherence tomography (OCT). RESULTS: Ptosis and external ophthalmoplegia progressively worsened during the follow-up, as did the neurological and general status. Corneal and optic disc alterations were also observed at the last visit. Glaucomatous changes of the optic disc were confirmed by the visual field examination and OCT. CONCLUSION: In addition to previously described alterations such as ptosis and external ophthalmoplegia, MNGIE may be associated with glaucomatous-like optic neuropathy.