Corneal reshaping: an experiment with a type I collagen-based vitrigel for remodeling porcine corneas / Remodelamento corneano: relato de um experimento com um vitrigel a base de colágeno tipo I para remodelamento de córneas porcinas

ABSTRACT Purpose: This study aimed to report an experiment designed to determine anatomical changes in porcine corneas following placement of a novel polymer implant into the cornea. Methods: An ex vivo porcine eye model was used. A novel type I collagen-based vitrigel implant (6 mm in diameter) was shaped with an excimer laser on the posterior surface to create three planoconcave shapes. Implants were inserted into a manually dissected stromal pocket at a depth of approximately 200 μm. Three treatment groups were defined: group A (n=3), maximal ablation depth 70 μm; Group B (n=3), maximal ablation depth 64 μm; and group C (n=3), maximal ablation depth 104 μm, with a central hole. A control group (D, n=3) was included, in which a stromal pocket was created but biomaterial was not inserted. Eyes were evaluated by optical coherence tomography (OCT) and corneal tomography. Results: Corneal tomography showed a trend for a decreased mean keratometry in all four groups. Optical coherence tomography showed corneas with implants placed within the anterior stroma and visible flattening, whereas the corneas in the control group did not qualitatively change shape. Conclusions: The novel planoconcave biomaterial implant described herein could reshape the cornea in an ex vivo model, resulting in the flattening of the cornea. Further studies are needed using in vivo animal models to confirm such findings.

RESUMO Objetivo: Relatar um experimento projetado para determinar alterações anatômicas em córneas porcinas após a colocação de um novo implante de polímero na córnea. Métodos: Foi utilizado olho de porco ex vivo. Um novo agente modelador biocompatível, de colágeno tipo 1, com 6mm de diâmetro foi moldado com excimer laser em sua face posterior, para criar três formatos planocôncavos. Os implantes foram inseridos dentro de um bolsão, dissecado manualmente, a 200 micrômetros (μm). Foram definidos três grupos de tratamento: grupo A (n=3), teve a profundidade máxima de ablação de 70 μm; o grupo B (n=3), profundidade máxima de ablação de 64 μm; e o grupo C (n=3), profundidade máxima de ablação de 104 μm, com buraco central. O grupo controle, D (n=3), foi incluído, com a criação do bolsão estromal, porém sem inserir o material. A avaliação desses olhos foi realizada por tomografia de coerência óptica (OCT) e por tomografia corneana. Resultados: A tomografia corneana mostrou uma tendência para diminuição da ceratometria média em todos os 4 grupos. A tomografia de coerência óptica mostrou córneas com implantes localizados no estroma anterior e aplanamento visível, enquanto as córneas não mudaram qualitativamente o formato no grupo controle. Conclusões: O novo implante de biomaterial planocôncavo descrito aqui foi capaz de remodelar a córnea em modelo de animal ex vivo, resultando no aplanamento corneano. Novos estudos são necessários usando modelos animais in vivo para confirmar tais achados.

Corneal reshaping: an experiment with a type I collagen-based vitrigel for remodeling porcine corneas.

PURPOSE: This study aimed to report an experiment designed to determine anatomical changes in porcine corneas following placement of a novel polymer implant into the cornea. METHODS: An ex vivo porcine eye model was used. A novel type I collagen-based vitrigel implant (6 mm in diameter) was shaped with an excimer laser on the posterior surface to create three planoconcave shapes. Implants were inserted into a manually dissected stromal pocket at a depth of approximately 200 µm. Three treatment groups were defined: group A (n=3), maximal ablation depth 70 µm; Group B (n=3), maximal ablation depth 64 µm; and group C (n=3), maximal ablation depth 104 µm, with a central hole. A control group (D, n=3) was included, in which a stromal pocket was created but biomaterial was not inserted. Eyes were evaluated by optical coherence tomography (OCT) and corneal tomography. RESULTS: Corneal tomography showed a trend for a decreased mean keratometry in all four groups. Optical coherence tomography showed corneas with implants placed within the anterior stroma and visible flattening, whereas the corneas in the control group did not qualitatively change shape. CONCLUSIONS: The novel planoconcave biomaterial implant described herein could reshape the cornea in an ex vivo model, resulting in the flattening of the cornea. Further studies are needed using in vivo animal models to confirm such findings.

Disconjugacy of Eye Movements during Attempted Fixation: A Sufficient Marker for Amblyopia?

BACKGROUND: To investigate whether detection of disconjugacy of eye movements during attempted fixation, or interocular position instability, may serve as a single sensitive test for amblyopia. PATIENTS/METHODS AND MATERIAL: Binocular eye movements were recorded at 500 Hz using the EyeLink 1000 eye tracker (SR Research Ltd., Kanata, Ontario, Canada) and analyzed using EyeLink software and Matlab (MathWorks, Natick, MA, USA). Eight subjects (four amblyopes, one successfully treated amblyope, and three non-amblyopes: 7 - 44 years) were asked to fixate on a stationary cross subtending 0.5° at 57 cm. Interocular position instability was quantified by calculating the minimum area bivariate contour ellipse (BCEA) encompassing 68% of the difference between right and left eye position points during 20-second viewing epochs. For statistical analysis, BCEA values, as well as visual acuity and stereoacuity, were normalized by base-10 logarithm transformation. RESULTS: The amblyopic subjects with persistent vision loss (one anisometropic, two strabismic, one deprivation; uncorrected visual acuity range 20/60 - 20/300, corrected stereoacuity range nil-400 arcsec) showed significantly higher interocular position instability (larger 68% BCEAs) than the non-amblyopic subjects (uncorrected visual acuity range 20/20 - 20/800, corrected stereoacuities of 20 arcsec) and the successfully treated strabismic amblyope (to the 20/20 level of visual acuity and 70 arcsec of stereoacuity) during binocular viewing trials; p < 0.01. Interocular position stability was strongly correlated with stereoacuity (in that better stereoacuity was associated with lower 68% BCEAs; r = 0.95), but not with visual acuity (r = 0.20). CONCLUSION: Interocular position instability appears to differentiate amblyopic from non-amblyopic subjects and appears to improve after successful treatment. Interocular position instability may therefore prove to be a single sensitive test for the presence of amblyopia. As a difference measure, it is inherently less susceptible to head motion and calibration error, as well as to conjugate eye motion, and as such is expected to be somewhat immune to latent nystagmus. Interocular position instability may also be useful to guide treatment, especially in preverbal children, and to assess the efficacy of novel treatments. Further research is required to establish optimal interocular position instability thresholds and to determine how specific this measure is to amblyopia.

How Lingering Fusional Adaptation Influences the Bielschowsky Head Tilt Test in Superior Oblique Paresis.

BACKGROUND: The lack of a positive Bielschowsky head tilt test (BHTT) is commonly seen as an indicator that superior oblique paresis (SOP) is not present. This study investigated the influence of fusion on the BHTT in unilateral SOP. PATIENTS/METHODS AND MATERIAL: We analyzed vertical fusional vergence using our eye-tracking haploscope and the value of BHTT difference (BHTTD) in 11 patients who were diagnosed with congenital unilateral SOP and able to fuse. RESULTS: Patients used one of three different mechanisms of vertical vergence to achieve fusion. The three fusional mechanisms were associated with a significantly different BHTTD (p < 0.05). Seven of the eleven patients used vertical recti-mediated fusion and had a mean BHTTD ± SD of 21.7 ± 6.3 prism diopters (PD). Three of these patients whom we measured after a patch test for at least 30 min showed a decreased BHTTD (12.7 ± 3.8 PD). Three of the eleven patients used a mixed (oblique/rectus) fusional mechanism and had a mean BHTTD ± SD of 9.3 ± 8.6 PD. Of these patients, the one whom we measured after patching showed an increase of 11 PD in BHTTD. The remaining patient used oblique muscle-mediated fusion and had a BHTTD of only 3 PD that increased to 21 PD after patching. One explanation for this BHTT behavior in the latter patient involves lingering vergence adaptation of the "paretic" superior oblique muscle (SOM) and contralateral inferior oblique muscle, which makes these muscles more effective when activated, as is the case on ipsilateral head tilt (part of the ocular counter-roll mechanism), lessening the expected increase in hyperdeviation. Similarly, in our patients with mixed fusion, the vergence-adapted "paretic" SOM and contralateral superior rectus muscle are activated on ipsilateral and contralateral tilt, respectively, lessening the hyperdeviation in both directions. In the other seven patients, however, the vergence-adapted ipsilateral inferior rectus muscle and contralateral superior rectus muscle are activated on contralateral tilt, accentuating the BHTTD. CONCLUSION: Depending upon the specific muscles used for vertical fusion, the BHTTD is decreased or increased. The presence of a large BHTTD points to lingering or persisting fusional tonus involving the vertical rectus muscles. The lack of a positive BHTT does not rule out the diagnosis of SOP, but rather may be caused by lingering or persevering fusional tonus involving the oblique muscles. Performing the BHTT after a patch test for a minimum of 30 minutes may be necessary to reveal the BHTTD, supporting the diagnosis of SOP.

Inferior Oblique Muscle "Overaction" Caused by Inferior Oblique Muscle Shortening, Not by Hypertonicity.

PURPOSE: To determine whether fusional vergence adaptation in patients who can fuse in at least some gaze positions can cause curvature of the non-fixing eye movement paths of patients with apparent "overaction" or "underaction" of the oblique muscles, yielding possibly erroneous evidence of hypertonicity as the cause of the overaction or underaction. METHODS: The authors retrospectively studied Lancaster red-green plots of patients with oblique muscle "overaction/underaction." If fusion was present, the plot had usually been repeated after monocular occlusion for at least 30 minutes. Fundus torsion and fusion status were also recorded. RESULTS: After a patch test in patients displaying fusion, the non-fixing eye's movement path became more linear. CONCLUSIONS: Although it has been argued that true overaction of the oblique muscles would show curved eye movement paths on side gazes, in the study patients displaying fusion in at least some directions of gaze, the eye movement paths became more linear after patch testing, favoring the more mechanical explanation. Illustrated cases were consistent with the hypothesis that short inferior oblique muscles simply hold the globes in extorted positions, and the appearance of inferior oblique muscle "overaction" arises from the eyes' following their extorted movement paths on side gazes, not from hypertonicity of the inferior oblique muscle in the adducting eye. [J Pediatr Ophthalmol Strabismus. 2022;59(1):28-34.].

Torsional incomitance after asymmetrically adjusted Harada-Ito procedures for the simultaneous correction of vertical and torsional deviations in bilateral trochlear nerve palsy.

BACKGROUND: Adjustable bilateral Harada-Ito procedures have been described, sometimes with asymmetric adjustment used to correct vertical misalignment when coexisting with torsional strabismus. We investigated the causes of significant postoperative torsional incomitance noted in some patients undergoing these procedures. METHODS: The medical records of patients who underwent bilateral Harada-Ito procedures for bilateral trochlear nerve palsy between 1980 and 2018 were reviewed retrospectively. Cases with simultaneous operation on any other oblique or vertical rectus muscle were excluded. Surgical results, especially using Lancaster red-green (Lan R-G) plots, were correlated with the procedures performed. RESULTS: A total of 17 patients were included. At their last follow-up visit (mean, 12 months after surgery), 9 were diplopia free. Of the 8 with continuing diplopia, 2 had undercorrection and 1 had Brown syndrome. In 5 patients with continuing diplopia, there was relative intorsion of the eye movement paths in upgaze and relative extorsion of these paths in downgaze, a type of torsional incomitance. Asymmetric adjustment with tightening of one superior oblique tendon, and often loosening of the contralateral superior oblique tendon, had been performed in those 5 cases. Only 1 of the successful cases had the same type of asymmetric adjustment. There was a positive association between the severity of the preoperative Lan R-G pattern and postoperative diplopia. CONCLUSIONS: Asymmetric adjustment of bilateral Harada-Ito procedures when attempting to correct the coexisting vertical misalignment can cause significant torsional incomitance with incomplete correction of extorsion in downgaze and intorsion in upgaze. This pattern may result in postoperative diplopia that is surgically challenging to correct.

Increasing incidence and risk factors for divergence insufficiency esotropia.

PURPOSE: To document the increasing incidence of divergence insufficiency (DI) esotropia and to identify risk factors for DI. METHODS: All patients with a diagnosis of esotropia seen by one provider (DLG) over 41 years were identified from the medical record. Patients with onset of strabismus before age 10 years or with prior strabismus surgery were excluded. Cases of esotropia associated with thyroid eye disease, scleral buckles, trauma, neurological diseases, or atypical misalignment were included but not labeled as DI regardless of the distance versus near deviation. The remaining patients, whatever the original diagnosis, were retrospectively categorized as having, or not having, DI, using a uniform criterion: distance esotropia ≥5Δ more than near esotropia. RESULTS: The percentage of DI patients among acquired esotropia patients increased significantly between the first and second half of the 41-year period, from 11.8% to 29.4% (P < 0.001). Multivariate logistic regression identified advancing age and the use of progressive addition lenses as risk factors for the development of DI. CONCLUSIONS: The incidence of DI is increasing. DI's association with age and progressive addition lenses may help us to understand its etiology and to decrease the prevalence of this condition in the future.

Meridional aniseikonia-causes, symptoms, and therapies.

BACKGROUND: The term aniseikonia refers to the two eyes' appreciating different image sizes when viewing the same object. Meridional aniseikonia can occasionally cause significant distortion of the binocular spatial sense in perceptive patients. METHODS: The medical records of 3 adult patients who complained of binocular spatial distortion consistent with meridional aniseikonia were reviewed retrospectively. Detailed descriptions of symptoms, ocular findings, and management are reported. RESULTS: Each patient had undergone a refraction-altering surgical procedure, and each complained of binocular spatial distortion characterized by a trapezoidal view of square or rectangular shapes. Each patient improved following management of the astigmatic correction. CONCLUSIONS: Patients requiring a new astigmatic correction following cataract or corneal surgery may complain of binocular spatial distortion caused by meridional aniseikonia.

Using IOLs for anterior segment photography in children.

We present a novel and convenient technique for obtaining clear, high-resolution anterior segment images using an expired intraocular lens (IOL) over the lens of a smartphone's camera. Our technique provides the means to acquire high-quality images when expensive anterior segment imaging devices are unavailable. A further advantage is decreasing the economic and environmental costs of expired IOLs, whose life can be extended through "recycling" as adjunctive camera lenses.

Adjustable suture strabismus surgery in infants and children: a 19-year experience.

PURPOSE: To evaluate the success rate of adjustable suture techniques in horizontal eye muscle surgery in children ≤15 years of age over a 19-year period by a single surgeon. METHODS: The medical records of all consecutive patients in this age group who underwent horizontal eye muscle surgery from 1989 through 2012 were reviewed retrospectively. Patients were divided into two groups: those in whom a nonadjustable suture technique was used and those in whom adjustable sutures were used. The following data were collected: type of strabismus, preoperative measurements, postoperative results, and reoperation rates. RESULTS: A total of 116 cases in the nonadjustable group and 521 cases in the adjustable group were included. In the adjustable group, adjustment was performed in 63% of the cases, because of either an under- (41%) or overcorrection (22%). The adjustment procedure was performed under topical proparacaine in 15% of cases and under intravenous propofol in 85%. For the adjustable group, 3-5 minutes more per muscle intraoperatively and 15-20 minutes for adjustment were required. No complications were encountered during the adjustment procedures. Early success rate, defined as alignment within 8Δ of straight at 3 to 6 months' postoperative follow-up, was significantly greater in the adjustable group than in the nonadjustable group (77.7% vs 64.6% [P ≤ 0.03]). Of the adjustable patients, 15% required reoperation compared with 21% of the nonadjustable patients. CONCLUSIONS: Use of adjustable sutures in horizontal eye muscle surgery in children ≤15 years of age provided an improved success rate and fewer reoperations compared with nonadjustable sutures.

A no-moving-parts sensor for the detection of eye fixation using polarised light and retinal birefringence information.

Polarised near-infra-red light is reflected from the foveal area in a detectable bow-tie pattern of polarisation states, offering the opportunity for eye tracking. A coaxial optical transducer was developed, consisting of a laser diode, a polariser, a filter, and a photodetector. Several such transducers may be used to interrogate different spots on the retina, thus eliminating the requirement for scanning systems with moving parts. To test the signal quality obtainable, using just one transducer, a test subject was asked to fixate successively on twelve targets located on a circle around the transducer, to simulate the retina's being interrogated by twelve sensors placed on a 30 diameter circle surrounding the projection of the fovea. The resulting signal is close to the "ideal" sine wave that would have been recorded from a propeller-type birefringence pattern from a human fovea. The transducer can be used in the detection of fixation for medical and other purposes. It does not require calibration, strict restrictions on head position, or head-mounted appliances.

Attention attraction in an ophthalmic diagnostic device using sound-modulated fixation targets.

This study relates to eye fixation systems with combined optical and audio systems. Many devices for eye diagnostics and some devices for eye therapeutics require the patient to fixate on a small target for a certain period of time, during which the eyes do not move and data from substructures of one or both eyes are acquired and analyzed. With young pediatric patients, a monotonously blinking target is not sufficient to retain attention steadily. We developed a method for modulating the intensity of a point fixation target using sounds appropriate to the child's age and preference. The method was realized as a subsystem of a Pediatric Vision Screener which employs retinal birefringence scanning for detection of central fixation. Twenty-one children, age 2-18, were studied. Modulation of the fixation target using sounds ensured the eye fixated on the target, and with appropriate choice of sounds, performed significantly better than a monotonously blinking target accompanied by a plain beep. The method was particularly effective with children of ages up to 10, after which its benefit disappeared. Typical applications of target modulation would be as supplemental subsystems in pediatric ophthalmic diagnostic devices, such as scanning laser ophthalmoscopes, optical coherence tomography units, retinal birefringence scanners, fundus cameras, and perimeters.

Nonabsorbable versus absorbable sutures in large, hang-back medial rectus muscle recessions.

PURPOSE: To investigate the value of nonabsorbable sutures in reducing the incidence of consecutive exotropia after large, "hang-back" medial rectus recessions. METHODS: The medical records of patients who underwent medial rectus recession of ≥6.5 mm in individuals ≤2 years of age, or ≥7.0 mm in those >2 years were retrospectively reviewed. Patients were divided into two groups based on suture material used: absorbable, polyglactin 910 sutures (44 patients); nonabsorbable, polyester sutures (50 patients). Preoperative measurements, ductions, strabismus surgery, and postoperative results were analyzed. Inadequate anchoring of the medial rectus muscle was suspected when consecutive exotropia developed 4-7 weeks after surgery after initial satisfactory alignment and was confirmed if during reoperation the medial rectus muscle appeared recessed >2 mm beyond the originally intended recession. RESULTS: Consecutive exotropia due to inadequate anchoring of the medial rectus muscle occurred in 11 of 66 muscles (17%) in the absorbable suture group. The muscle was found 6-10 mm posterior to the intended recession. Limited duction in the field of action of the involved medial rectus muscle occurred in 9 of the 11 muscles (82%). None of the eyes with nonabsorbable sutures showed inadequate anchoring. The incidence of consecutive exotropia was higher in the absorbable suture group (30%) than in the nonabsorbable suture group (6%) (P < 0.005). CONCLUSIONS: Using nonabsorbable suture for large, hang-back medial rectus recessions greatly reduces the incidence of consecutive exotropia that can occur when absorbable suture dissolves.

Deficiency of depression in adduction: clinical characteristics and surgical management of the "inverted Brown pattern".

PURPOSE: To evaluate the clinical characteristics and surgical management of patients with an "inverted Brown pattern," which is defined clinically as a hypertropia with greatest deviation in down-and-in gaze of the higher eye, having the appearance of superior oblique muscle underaction but without significant inferior oblique muscle overaction. METHODS: The medical records of patients with this misalignment pattern who had cyclovertical muscle surgery at our institution from 2003 through 2015 were retrospectively reviewed; medical records were analyzed for pre- and postoperative motility patterns, fundus torsion, intraoperative findings, and type of strabismus surgery. RESULTS: A total of 45 patients presenting with a hyperdeviation worse in down-and-in gaze of the higher eye were included in the study. Of these, 25 (56%) had previously had inferior oblique-weakening procedures. The remainder included those with untreated superior oblique paresis (22%), previous orbital trauma (18%), or other ocular surgery (4%). The mean preoperative hyperdeviation in straight-ahead gaze was 8.7(Δ), compared with 0.9(Δ) postoperatively. Surgical success, defined as the absence of diplopia in straight-ahead gaze and not requiring further cyclovertical surgery, was achieved in 78% of patients. CONCLUSIONS: The motility pattern referred to as the "inverted Brown pattern" can develop in patients with orbital trauma, as previously described, or in association with superior oblique muscle paresis, most commonly after prior surgery to weaken the inferior oblique muscle. Weakening or reweakening of the inferior oblique muscle appears to correct this misalignment pattern, despite the absence of significant inferior oblique overaction preoperatively.

New pediatric vision screener, part II: electronics, software, signal processing and validation.

BACKGROUND: We have developed an improved pediatric vision screener (PVS) that can reliably detect central fixation, eye alignment and focus. The instrument identifies risk factors for amblyopia, namely eye misalignment and defocus. METHODS: The device uses the birefringence of the human fovea (the most sensitive part of the retina). The optics have been reported in more detail previously. The present article focuses on the electronics and the analysis algorithms used. The objective of this study was to optimize the analog design, data acquisition, noise suppression techniques, the classification algorithms and the decision making thresholds, as well as to validate the performance of the research instrument on an initial group of young test subjects-18 patients with known vision abnormalities (eight male and 10 female), ages 4-25 (only one above 18) and 19 controls with proven lack of vision issues. Four statistical methods were used to derive decision making thresholds that would best separate patients with abnormalities from controls. Sensitivity and specificity were calculated for each method, and the most suitable one was selected. RESULTS: Both the central fixation and the focus detection criteria worked robustly and allowed reliable separation between normal test subjects and symptomatic subjects. The sensitivity of the instrument was 100 % for both central fixation and focus detection. The specificity was 100 % for central fixation and 89.5 % for focus detection. The overall sensitivity was 100 % and the overall specificity was 94.7 %. CONCLUSIONS: Despite the relatively small initial sample size, we believe that the PVS instrument design, the analysis methods employed, and the device as a whole, will prove valuable for mass screening of children.

Mechanisms of Vertical Fusional Vergence in Patients With "Congenital Superior Oblique Paresis" Investigated With an Eye-Tracking Haploscope.

PURPOSE: To determine the mechanisms of vertical fusional vergence in patients with "congenital unilateral superior oblique paresis" (SOP) and to discuss the implications of these mechanisms. METHODS: Eleven patients were examined with our eye-tracking haploscope. RESULTS: Three different fusion mechanisms were found, producing significantly different cyclovergence to vertical vergence ratios (P < 0.05): primary use of the vertical rectus muscles in seven patients (ratio: 0.36 ± 1.6), primary use of the oblique muscles in one patient (0.04), and use of the superior oblique muscle in the higher eye and the superior rectus muscle in the lower eye in three patients (1.15 ± 0.32). Lancaster red-green testing showed alignment differences among these groups, primarily differences in amount of subjective extorsion between the two eyes in straight-ahead gaze: The patient with oblique-muscle-mediated fusion showed essentially no subjective extorsion (0.5°), the patients with vertical-rectus-muscle-mediated vertical fusion showed a mean ± SD subjective extorsion of 3.6° ± 1.4°, and the patients with the mixed (oblique/rectus) fusion mechanism showed 7.0° ± 1.7° (P < 0.05). CONCLUSIONS: The choice of fusion mechanism may be a function of how much intorting effect is needed. Use of the oblique muscles bilaterally causes the least intorting effect, use of the vertical rectus muscles bilaterally adds more intorting effect, and activation of the "paretic" superior oblique muscle in the higher eye and the superior rectus muscle in the lower eye provides the greatest intorting effect. Subclassifying "congenital SOP" in this way (in which the "paretic" muscle may remain functional in many cases) may help guide its optimal surgical correction.