Experimental imaging of intracorneal ring segments with optical coherence tomography

PURPOSE: To investigate the imaging of corneal structures with optical coherence tomography (OCT) after implantation of intracorneal ring segments (ICRS). METHODS: In an experimental study with six porcine eyes, qualitative and quantitative imaging with corneal OCT using a wavelength of 1310 nm after implantation of ICRS was performed. The optical results were compared with light microscopy of the histological sections. RESULTS: In corneal OCT, the ICRS revealed marked hyporeflective intrastromal areas, which correlated well with macroscopic and microscopic findings. Corneal OCT enabled precise images of the incision depth for the implantation of ICRS, and the exact intrastromal segment position. CONCLUSIONS: Noncontact slit lamp-adapted corneal optical coherence tomography could be employed to clinically monitor corneal changes after implantation of ICRS, evaluate the depth of the segments to correlate refractive changes, and quantify the stromal wound healing response.     

Optical coherence tomography imaging in keratoconus

Optical coherence tomography (OCT) is being increasingly used as a tool in the diagnosis and management of keratoconus. While elevation‐based topography remains essential, there is an expanding role for cross‐sectional OCT imaging in the diagnosis of the disease. Images and measurements of corneal thickness, and in particular, epithelial thickness, may be important in diagnosing early cases, and following procedures such as intrastromal corneal ring segments, corneal transplants and corneal collagen cross‐linking.     

High-speed optical coherence tomography for management after laser in situ keratomileusis

PURPOSE: To report applications of optical coherence tomography (OCT) in the management of laser in situ keratomileusis (LASIK) related problems. SETTING: Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California, USA. METHODS: Five patients referred for LASIK-related problems were enrolled in a prospective observational study. Clinical examination, ultrasound (US) pachymetry, Placido ring slit-scanning corneal topography (Orbscan II, Bausch & Lomb), and high-speed corneal OCT were performed. RESULTS: In cases of regression and keratectasia, OCT provided thickness measurements of the cornea, flap, and posterior stromal bed. Locations of tissue loss and flap interface planes were identified in a case with a recut enhancement complication. The information was used to determine whether further laser ablation was safe, confirm keratectasia, and manage complications. Optical coherence tomography measurements of central corneal thickness agreed well with US pachymetry measurements (difference 6.4 microm +/- 11.7 [SD]) (P = .026), while Orbscan significantly underestimated corneal thickness (-67.5 +/- 72.5 microm) (P = .17). CONCLUSIONS: High-speed OCT provided noncontact imaging and measurement of LASIK anatomy. It was useful in monitoring LASIK results and evaluating complications.     

Intrastromal corneal ring segments in a patient with previous laser in situ keratomileusis

PURPOSE: Intrastromal corneal ring segments (ICRS; Intacs) were inserted in a patient with residual myopia of -3.375 D (spherical equivalent) 10 months after laser in situ keratomileusis (LASIK). METHODS: A standard intrastromal corneal ring segment implantation technique was used with the addition of intraoperative ultrasonic pachymetry in 4 quadrants at the 7-mm zone to insure adequate stromal thickness for segment insertion. RESULTS: Four months after ICRS surgery and 14 months after LASIK, the patient had uncorrected visual acuity of 20/20 and a cycloplegic refraction of plano -1.00 x 23 degrees. CONCLUSION: Implantation of intrastromal corneal ring segments in an eye with previous LASIK resulted in additional corneal flattening with a decrease in residual myopia and improved uncorrected visual acuity.     

Evaluation of granular corneal dystrophy with optical coherent tomography

OBJECTIVE: To determine the intrastromal layer of corneal deposits in granular corneal dystrophy (GCD). DESIGN: Investigative case report. METHODS: A 32-year-old woman with bilateral decreased vision because of corneal deposits was examined with cross-sectional scans using optical coherence tomography (OCT). RESULTS: Visual acuity was 20/100 OU. Multiple confluent gray-white patches with an irregular shape were seen in the corneal stroma, leading to a diffuse opacification. OCT disclosed multiple hyperreflective dots in the anterior and deeper stromal layers. CONCLUSION: When severe corneal opacities obscure the clinical differentiation between anterior and deep infiltrates, OCT may determine the layers of the accumulation and select an appropriate surgical procedure.     

Optical coherence tomography for evaluation of anatomical changes in the cornea after laser in situ keratomileusis

PURPOSE: To examine the use of optical coherence tomography (OCT) in evaluating anatomical changes after laser in situ keratomileusis (LASIK) and complications related to the interface and corneal flap. SETTING: Istanbul University Eye Research Center and Department of Ophthalmology, Cerrahpasa Medical School, Istanbul, Turkey. METHODS: Eleven eyes of 11 patients who had myopic LASIK were included in the study. Mean age of the 7 men and 4 women was 29.4 years +/- 6.9 (SD). Cases analyzed included uneventful LASIK (4 eyes), epithelial ingrowth (5 eyes), and flap striae (2 eyes). Corneas were examined by OCT (Humphrey Systems). RESULTS: Optical coherence tomography resolved corneal flap and residual stromal layers in all cases. The mean thickness of the corneal flap and residual stroma was 138.2 +/- 16.5 microm and 321.7 +/- 32.1 microm, respectively. Interface between the corneal flap and residual stroma was shown by OCT. Optical coherence tomography revealed that the eye with flap striae had flap displacement undetected by biomicroscopy. Epithelial ingrowth was shown as a highly reflective area. CONCLUSION: Optical coherence tomography appears to be a promising method for evaluating anatomical changes in the cornea after LASIK.     

Donor disc attachment assessment with intraoperative spectral optical coherence tomography during descemet stripping automated endothelial keratoplasty

Optical coherence tomography has already been proven to be useful for pre- and post-surgical anterior eye segment assessment, especially in lamellar keratoplasty procedures. There is no evidence for intraoperative usefulness of optical coherence tomography (OCT). We present a case report of the intraoperative donor disc attachment assessment with spectral-domain optical coherence tomography in case of Descemet stripping automated endothelial keratoplasty (DSAEK) surgery combined with corneal incisions. The effectiveness of the performed corneal stab incisions was visualized directly by OCT scan analysis. OCT assisted DSAEK allows the assessment of the accuracy of the Descemet stripping and donor disc attachment.     

Intrastromal corneal segments implantation in keratoconus

Up-to-date models of intrastromal corneal segments are reviewed. Different techniques of up-to-date models of intrastromal corneal segments implantation in keratoconus are described. Mechanical and laser techniques of forming of corneal tunnels are analyzed. Information about potential complications of intrastromal corneal segment implantation is given.     

Corneal thickening and central flattening induced by femtosecond laser hyperopic-shaped intrastromal lenticule implantation

Purpose

To investigate the feasibility of the procedure and the modifications of the corneal curvature and profile obtained with a novel technique of stromal-lentoid implantation in ex vivo human corneas.

Design

Experimental ex vivo study in human corneas.

Materials and methods

Twelve stromal lentoids were produced by means of hyperopic femtosecond lenticule extraction (FLEx) with the VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany) with a refractive power of +8.00 D and optical zone of 6.0 (six lenticules) and 5.0 mm (six lenticules), respectively. The posterior surface of these stromal lentoids presented a higher curvature with respect to the anterior surface and, therefore, the thinnest point is located at the center of the lenticule, gradually thickening towards the periphery. Another 12 corneas underwent femtosecond laser intrastromal pocket creation at a depth of 115 microns, for lenticule insertion. After intrastromal lenticule implantation the changes of corneal profiles were evaluated by means of corneal topography and anterior segment optical coherence tomography (OCT).

Results

The implantations of intrastromal lenticules were successful in all cases with proper distention and centration. A mid-peripheral forward shift of the anterior corneal surface along with a thickening (greater in periphery) was induced. There was a significant flattening of anterior corneal central areas of 7.31 ± 1.52 D (p = 0.002). Diameters of the flattening area were found to be consistently correlated with the optical zone diameter of the implanted lenticules (p = 0.006). Central flattening was similar in both groups. OCT pachymetry maps showed an increase of corneal thickness consistently correlated with implanted lentoid thickness and diameter.

Conclusion

The implantation of modified hyperopic-shaped intra-corneal stromal lentoid is a feasible and reproducible technique for achieving central corneal flattening while increasing thickness. Whether this procedure may be beneficial in the treatment of refractive errors or ectatic corneal disorders such as keratoconus merits further study.

     

Intraocular pressure measurement in patients with instrastromal corneal ring segments.

PURPOSE: To study the measurement of intraocular pressure after implantation of Intacs (ICRS) intrastromal corneal ring segment, a device that is positioned circumferentially in the peripheral corneal stroma to correct myopia. The device changes the corneal curvature by shortening arc length. Since the ring segments are made of polymethylmethacrylate, this may cause localized changes in corneal elasticity so intraocular pressure measurement may be affected. METHODS: We measured the intraocular pressure of 12 eyes in which the ICRS had been in place longer than 6 months. We used Goldmann applanation and Tono-Pen tonometers over the central corneal and the paracentral corneal areas. We also measured the intraocular pressure with the Tono-Pen applanated directly over the intrastromal corneal ring segments. RESULTS: The resulting intraocular pressure measurements were similar for the Tono-Pen tonometer readings over the central cornea, paracentral cornea, and the Goldmann applanation tonometer readings over the central cornea (P < .01). Our measurements using the Goldmann applanation tonometer on the paracentral corneal area showed artificially elevated intraocular pressure in the 40 to 60 mmHg range. We were not able to obtain consistent results when we measured the intraocular pressure using the Tono-Pen on the corneal area directly overlying the intrastromal corneal ring segment implants. CONCLUSION: Consistent intraocular pressure measurements on eyes with the ICRS can be obtained with the Goldmann applanation tonometer over the central corneal area or with the Tono-Pen tonometer over the central or paracentral corneal areas.     

Anterior Segment Optical Coherence Tomography

Optical coherence tomography (OCT) is a non-contact optical signal acquisition and processing device that provides magnified, high resolution cross-sectional images of ocular tissues. Development of anterior segment OCT (AS-OCT) offers the benefits of fine resolution and noninvasive examination to investigation of anterior segment anatomy to the depth of the iris plane. This imaging device has been utilized for investigation into a myriad of corneal and anterior segment disease. Recent technological advances toward three-dimensional visualization broaden the scope of AS-OCT in ophthalmologic evaluation. The AS-OCT is a valuable imaging tool whose use in research and clinical practice will continue to expand our knowledge and management of various ophthalmic conditions.     

Anterior segment optical coherence tomography

Optical coherence tomography (OCT) is a non-contact optical signal acquisition and processing device that provides magnified, high resolution cross-sectional images of ocular tissues. Development of anterior segment OCT (AS-OCT) offers the benefits of fine resolution and noninvasive examination to investigation of anterior segment anatomy to the depth of the iris plane. This imaging device has been utilized for investigation into a myriad of corneal and anterior segment disease. Recent technological advances toward three-dimensional visualization broaden the scope of AS-OCT in ophthalmologic evaluation. The AS-OCT is a valuable imaging tool whose use in research and clinical practice will continue to expand our knowledge and management of various ophthalmic conditions.     

Optical Coherence Tomography Findings in Anterior Chamber Ointment Globule after Phacoemulsification

We present 2 cases of anterior chamber ointment with evidence of progressive endothelial cell loss. In both cases, an anterior segment optical coherence tomography (OCT) was similar to an OCT of a tobramycin-dexamethasone ointment placed on a pen tip. An anterior segment OCT also demonstrated the direct contact of the globule with the corneal endothelium. A gas chromatography/mass spectrometry analysis documented the similarity to tobramycin-dexamethasone ointment in 1 case. Anterior segment OCT can help in confirming the diagnosis. Corneal endothelial injury is a continuous process, and its clinical manifestation is related to the size of the globule, the initial endothelium count, and the duration of ointment contact, which is related to supine positioning. It is advisable to avoid ointments in the immediate postoperative period, especially in corneal wounds larger than 3 mm.Key Words: Optical coherence tomography, Anterior chamber ointment globule, Phacoemulsification     

Continuous monitoring of corneal thickness changes during LASIK with online optical coherence pachymetry

PURPOSE: To assess the continuous intraoperative monitoring of central corneal thickness (CCT) changes during laser in situ keratomileusis (LASIK) using online optical coherence pachymetry (OCP). SETTING: Department of Ophthalmology, Vivantes Klinikum Neukolln, Berlin, Germany. METHODS: In this prospective nonrandomized comparative clinical case series of consecutive patients, 32 eyes having LASIK for myopia, myopic astigmatism, or hyperopia were continuously monitored intraoperatively in real time with online OCP integrated into a clinical excimer laser. The intraoperative values were compared to the postoperative flap and residual stromal thicknesses measured with corneal optical coherence tomography (OCT) as well as the calculated myopic ablation depth. RESULTS: Continuous monitoring with online OCP enabled intraoperative visualization of the CCT changes during LASIK. The CCT, flap thickness after the microkeratome pass, time-resolved ablation, and residual stromal thickness were assessed. Intraoperatively, the mean flap thickness was 135 microm +/- 38 (SD) and the mean residual stromal thickness, 286 +/- 59 microm. The mean intraoperative flap and residual stromal thickness values were 43.7 microm and 15.4 microm lower, respectively, than the postoperative values assessed with corneal OCT (P<.001 and P=.005, respectively). The optically determined myopic ablation depth was 118 +/- 37 microm, which was 28 microm higher than the nominal ablation depth. There was a significant correlation (P<.001) between the postoperative flap (r=0.79) and residual (r=0.88) thickness measured with corneal OCT as well as the calculated myopic ablation depth (r=0.95). CONCLUSIONS: Intraoperative online OCP could be an important safety feature to monitor the flap and residual stromal thicknesses during LASIK. The individual ablation depth and possible dehydration effects were also monitored continuously.     

Flap thickness reproducibility in laser in situ keratomileusis with a femtosecond laser: optical coherence tomography measurement

PURPOSE: To compare ultrasound (US) pachymetry, Orbscan, and optical coherence tomography (OCT) measurements of the central corneal thickness (CCT) before laser in situ keratomileusis (LASIK) and evaluate the reproducibility of flaps created with the IntraLase femtosecond laser (IntraLase, Inc.) using OCT. SETTING: Department of Ophthalmology, IIsan Paik Hospital, Goyang, Korea. METHODS: Central corneal thickness was measured using OCT, US pachymetry, and Orbscan in 59 eyes of 30 patients before femtosecond laser LASIK. The postoperative corneal flap thickness, measured using OCT, was compared with the preoperative intended thickness. RESULTS: Optical coherence tomography, US pachymetry, and Orbscan measurements provided similar CCT values (P>.05). Corneal thickness values obtained using US or Orbscan correlated well with those obtained by OCT, with the correlation coefficient ranging from 0.804 to 0.889 (P<.05). The OCT measurements showed no significant difference between the postoperative flap thickness and the intended flap thickness (P>.05). CONCLUSIONS: Optical coherence tomography was comparable to US pachymetry and Orbscan in cornea thickness measurement. Optical coherence tomography was easy and relatively accurate to use preoperatively and in the early postoperative period. The femtosecond laser created highly reproducible flaps that corresponded with the preoperative intended thickness.     

Ferrara intrastromal corneal ring segments for severe keratoconus

PURPOSE: Intrastromal Ferrara ring segments were inserted in eyes with severe keratoconus to evaluate safety and efficacy of this procedure. METHODS: Intrastromal Ferrara ring segments were placed in 36 eyes of 35 patients with severe keratoconus, who were evaluated after 12 months of follow-up. All patients had highly disabling visual acuity, contact lens intolerance, and a previous indication for penetrating keratoplasty. Statistical analysis included preoperative and postoperative uncorrected visual acuity, best spectacle-corrected visual acuity, manifest refraction, anterior chamber depth, keratometry, and pachymetry. RESULTS: No patient had a loss of visual acuity. Uncorrected visual acuity improved in 28 eyes (77.78%) and best spectacle-corrected visual acuity improved in 29 eyes (80.56%). Spherical equivalent refraction decreased from -7.29 +/- 3.12 D to -4.80 +/- 3.04 D at 12 months after Ferrara intrastromal ring segment implantation. Corneal topography and ultrasound biomicroscopy showed corneal flattening, demonstrated by thinning of the central cornea and a reduction in anterior chamber depth. Segment decentration occurred in one eye (2.7%), asymmetric positioning of the segments in two eyes (5%), inadequate depth in two eyes (5%), migration of the segments in two eyes (5%), segment extrusion in five eyes (13.8%), conjunctivitis in one eye (2.7%), bacterial keratitis in one eye (2.7%), and hydrops in one eye (2.7%). CONCLUSIONS: With these early results, Ferrara intrastromal ring segments appear to be an alternative for the treatment of severe keratoconus.     

Corneal and epithelial thickness in keratoconus: a comparison of ultrasonic pachymetry, Orbscan II, and optical coherence tomography

PURPOSE: To compare corneal thickness measurements in individuals with keratoconus using optical coherence tomography (OCT), Orbscan II, and ultrasonic pachymetry and to measure epithelial and stromal thickness in these individuals using OCT. METHODS: Twenty individuals with keratoconus and 20 controls (without keratoconus) were enrolled. The Orbscan II was used to locate the steepest area of the cornea, which was taken to represent the cone apex. Each instrument was used to obtain four total corneal thickness measurements-from the cone apex, corneal center, mid-nasal, and mid-temporal cornea. Optical coherence tomography scans were analyzed to provide epithelial and stromal thickness readings. RESULTS: In individuals with keratoconus, mean central corneal thickness (CCT) measured by ultrasonic pachymetry, Orbscan, and OCT was 494.2 +/- 50.0 microm, 438.6 +/- 47.7 microm, and 433.5 +/- 39.7 microm, respectively. The central keratoconic cornea was 57.7 microm thinner than the normal cornea (post-hoc P<.001). The cone apex was thinner than the central cornea (P<.001). Keratoconic epithelium was 48.2 +/- 5.5 microm centrally and 42.1 +/- 4.5 microm at the apex. Central keratoconic epithelium was 4.7 microm thinner and central keratoconic stroma was 57.8 microm thinner than the normal cornea (P<.001, respectively). Comparing instruments, Orbscan and OCT correlated in CCT measurement (r=0.890) and apical thickness (r=0.846). All instruments produced similar readings for mid-nasal and mid-temporal corneal thickness in participants with keratoconus (P>.05). CONCLUSIONS: Ultrasonic pachymetry produced the highest corneal thickness readings in the center and apex, compared to Orbscan II and OCT. Centrally, the total cornea, epithelium, and stroma were thinner in individuals with keratoconus than in normal individuals.     

Imaging scleral expansion bands for presbyopia with optical coherence tomography

A 57-year-old woman was treated for mild presbyopia with implantation of scleral expansion bands (SEB). Although near vision was temporarily restored, the effect dissipated after 1 year. Slitlamp-adapted optical coherence tomography (OCT) at 1310 nm allowed precise cross-sectional visualization of the hyporeflective intrascleral segments. The OCT method provided precise images of the segment depth and thickness, the scleral thickness at the scleral spur, the anterior chamber angle, and the angle-opening distance. Intrascleral tilting of 1 segment was seen; this required removal of the SEB because of marked foreign-body sensation. Noncontact, slitlamp-adapted OCT can be used to evaluate scleral changes after SEB implantation.     

Intrastromal corneal ring segments: visual outcomes from a large case series

Background: To evaluate the clinical safety and efficacy of implanted Ferrara intrastromal corneal ring segments in a large sample of patients with ectatic corneal disease. Design: Retrospective, consecutive case series. Samples: A total of 1073 eyes of 810 patients consecutively operated from January 2006 to July 2008 were evaluated. Methods: Two groups were created according to the type of ring implanted: Group 1 – patients implanted with the 160° of arc ring – and Group 2 – patients implanted with the 210° of arc ring. Main Outcome Measures: Uncorrected visual acuity, best‐corrected visual acuity, keratometry, asphericity and pachymetry at the thinnest point of the cornea. All patients were evaluated using a corneal tomography (Pentacam, Oculus, Inc., Lynnwood, WA, USA). Results: For Group 1 patients, uncorrected visual acuity increased to 20/80, best‐corrected visual acuity increased to 20/40, asphericity decreased to ?0.35, spherical equivalent decreased to ?2.26 D and keratometry decreased to 45.72 D (P < 0.001 for each compared with preoperative values). For Group 2 patients, uncorrected visual acuity increased to 20/130, best‐corrected visual acuity increased to 20/60, asphericity decreased to ?0.56, spherical equivalent decreased to ?4.14 D and keratometry decreased to 48.10 D (P < 0.001 for each compared with preoperative values). The 210° intrastromal corneal ring segments reduced keratometry and asphericity more than the 160° intrastromal corneal ring segments did. The complication rate was 3.82%. Conclusions: Ferrara intrastromal corneal ring segments implantation is safe and effective and has a low complication rate. It can effectively reduce the corneal steepening and improve uncorrected visual acuity and best‐corrected visual acuity in patients with keratoconus.     

Clinical and research applications of anterior segment optical coherence tomography – a review

Optical coherence tomography (OCT) is being employed more and more often to image pathologies and surgical anatomy within the anterior segment, specifically in anterior chamber biometry, corneal pachymetric mapping, angle evaluation and high-resolution cross-sectional imaging. The cross-sectional imaging capability of OCT is similar to ultrasound, but its higher resolution allows OCT to measure and visualize very fine anatomic structures. No contact is required. In this review, we describe the utility and limitations of anterior segment OCT.