[Blue light and intraocular lenses (IOLs): Beliefs and realities]. / Lumière bleue et implants intraoculaires : croyances et réalités.

The first intraocular lenses (IOLs) used for cataract surgery transmitted both ultraviolet (UV) radiation and visible light to the retina. Colorless UV-blocking IOLs were introduced and rapidly adopted in the 1980s. Yellow-tinted blue-blocking (also known as blue-filtering) IOLs were marketed in the early 1990s. Blue-blocking IOLs were intended to simulate age-related crystalline lens yellowing to reduce the cyanopsia that some patients experienced after cataract surgery. When blue-filtering IOLs were introduced in North America, however, blue-blocking chromophores were advocated as a way to protect patients from age-related macular degeneration (AMD) despite the lack of evidence that normal environmental light exposure causes AMD. The "blue light hazard" is a term that describes the experimental finding that acute, abnormally intense light exposures are potentially more phototoxic to the retina when short rather than long wavelengths are used. Thus, in brief exposures to intense light sources such as welding arcs, ultraviolet radiation is more hazardous than blue light, which is more hazardous than longer wavelength green or red light. International commissions have cautioned that the blue light hazard does not apply to normal indoor or outdoor light exposures. Nonetheless, the hazard is used for commercial purposes to suggest misleadingly that ambient environmental light can cause acute retinal phototoxicity and increase the risk of AMD. Very large epidemiological studies show that blue-blocking IOLs do not reduce the risk or progression of AMD. Additionally, blue-filtering IOLs or spectacles cannot decrease glare disability, because they decrease image and glare illuminance in the same proportion. Blue light is essential for older adults' scotopic photoreception needed to reduce the risk of nighttime falling and related injuries. It is also critical for circadian photoreception that is essential for good health, sleep and cognitive performance. Unfortunately, age-related pupillary miosis, retinal rod and ganglion cell photoreceptor degeneration and decreased outdoor activity all reduce the amount of healthful blue light available to older adults. Blue-restricting IOLs further reduce the available blue light at a time when older adults need it most. Patients and ophthalmologists are exposed to hypothesis-based advertisements for blue-filtering optical devices that suppress short wavelength light critical for vision in dim lighting and for good physical and mental health. Spectacle and intraocular lens selections should be based on scientific fact, not conjecture. Ideal IOLs should improve photoreception rather than limit it permanently. Practice efficiency, surgical convenience and physician-manufacturer relationships may eliminate a patient's opportunity to choose between colorless blue-transmitting IOLs and yellow-tinted, blue-restricting IOLs. Cataract surgeons ultimately determine whether their patients have the opportunity to make an informed choice about their future photoreception.

Descemet's membrane endothelial keratoplasty rejection after SARS-COV2 infection or vaccination: 2-year retrospective study.

PURPOSE: To assess the incidence of Descemet's membrane endothelial keratoplasty (DMEK) rejection potentially associated with coronavirus disease 2019 (COVID-19) infection or vaccination, and its association with known rejection risk factors during the first two years of the pandemic. METHODS: This retrospective study included patients with DMEK rejection between January 2020 and December 2021. Diagnostic criteria were based on symptoms, visual acuity, and other clinical assessments. Risk factors for graft rejection were considered, and a telephone survey was conducted to identify possible preceding COVID-19 infection or vaccination. RESULTS: Of 58 patients, 44 were included. Six patients (14%) reported COVID-19 infection, with one immediate endothelial graft rejection (EGR) post-infection. After vaccine availability, 13 of 36 patients had EGR at an average of 2.7 months post-vaccination. Five (38%) had immediate EGR following vaccination, four of which had concomitant risk factors for rejection. CONCLUSION: Although the risk of endothelial graft rejection (EGR) associated with COVID-19 infection or vaccination appears to be extremely low, there may be a causative relationship, especially in patients with pre-existing risk factors for EGR. A temporary increase in anti-rejection treatment following COVID-19 infection or vaccination is recommended, especially in patients with pre-existing risk factors, along with closer monitoring during the subsequent 4 to 8 weeks.

Success of ChatGPT, an AI language model, in taking the French language version of the European Board of Ophthalmology examination: A novel approach to medical knowledge assessment.

PURPOSE: The purpose of this study was to evaluate the performance of ChatGPT, a cutting-edge artificial intelligence (AI) language model developed by OpenAI, in successfully completing the French language version of the European Board of Ophthalmology (EBO) examination and to assess its potential role in medical education and knowledge assessment. METHODS: ChatGPT, based on the GPT-4 architecture, was exposed to a series of EBO examination questions in French, covering various aspects of ophthalmology. The AI's performance was evaluated by comparing its responses with the correct answers provided by ophthalmology experts. Additionally, the study assessed the time taken by ChatGPT to answer each question as a measure of efficiency. RESULTS: ChatGPT achieved a 91% success rate on the EBO examination, demonstrating a high level of competency in ophthalmology knowledge and application. The AI provided correct answers across all question categories, indicating a strong understanding of basic sciences, clinical knowledge, and clinical management. The AI model also answered the questions rapidly, taking only a fraction of the time needed by human test-takers. CONCLUSION: ChatGPT's performance on the French language version of the EBO examination demonstrates its potential to be a valuable tool in medical education and knowledge assessment. Further research is needed to explore optimal ways to implement AI language models in medical education and to address the associated ethical and practical concerns.

[Epigenetics and myopia: Mechanisms and therapeutic targets]. / Épigénétique et myopie : mécanismes et perspectives thérapeutiques.

The development of myopia is influenced by multiple environmental and genetic factors. A third component, epigenetics, may shed light on some of the relationships between environmental and genetic factors. Epigenetics is defined as the study of modulations of gene activity that can be transmitted over cell divisions without involving mutation of the DNA sequence. Methylation is one of the main mechanisms by which gene expression is decreased. In the context of myopia, the study of epigenetic mechanisms also contributes to the understanding of the involvement of candidate genetic variants. The analysis of metabolic and signalling pathways associated with ocular development enables discussion of the biological significance associated with these candidate genes. A better understanding of epigenetic mechanisms would allow individual risk estimations for myopia and probably targeting of therapeutic interventions at a population level. Measuring the level of DNA methylation at candidate gene sites could be used to monitor the effectiveness of myopia prevention measures such as reducing near work and increasing outdoor activity. More specifically, one could consider activating the methylation of myopia promoter genes or, on the contrary, inhibiting the methylation of myopia repressor genes. Finally, the control of metabolic and signalling pathways could be considered by targeting, for example, the regulation of the G protein signalling pathway (RGS 2) with the expression of the adenosine A2a receptor (AdoRs).

Surgical approaches to autologous limbal stem cell transplantation (LSCT) following severe corneal chemical burns.

Chemical injury of the conjunctiva and cornea are true ocular emergencies and require immediate intervention. They can produce severe, extensive ocular damage, including limbal stem cell deficiency (LSCD), and lead to irreversible visual loss. LSCD can be treated surgically through autologous limbal stem cell transplantation (LSCT). Autologous LSCT can be performed through cultivated limbal epithelial transplantation (CLET) or by direct grafting of limbal epithelial cells through conjunctival-limbal autografting (CLAU) or simple limbal epithelial transplantation (SLET). In this review we provide an overview of each surgical approach. CLET allows for a implantation of a large graft in the recipient eye while preserving donor cells. Its success rate is higher with an increased number of transplanted stem cells; failures tend to occur within the first year. CLAU is performed by directly transplanting autologous limbal stem cells from the patient's healthy eye, reducing the risk of immune rejection. This constitutes a risk for the donor eye, as the removal of stem cells from the fellow eye may lead to LSCD in the donor eye. SLET consists of direct implantation of donor stem cells on an amniotic membrane, thus avoiding the need for ex-vivo expansion. Combinations of CLAU and SLET within a single procedure have also been successfully utilized. Autologous LCST is an effective technique for surgical management of unilateral LCSD. Depending on the patient history and status of the fellow eye, either CLET, CLAU or SLET (including the combination of mini-CLAU and SLET) can be used to restore long-term function and prevent visual impairment.

Non stripping descemet membrane endothelial keratoplasty in difficult cases: A case series.

Endothelial keratoplasty (EK) has been increasingly used instead of penetrating keratoplasty (PK) in the management of post PK graft rejection. Both DSAEK and DMEK involve the surgical removal of the diseased host endothelial cell layer and Descemet's membrane (DM) (descemetorhexis) before transplantation, a technically challenging step, especially in post-PK eyes. Understandably, interest arose when non-stripping DMEK (nDMEK) was described in 2013, and recent studies suggested encouraging results without increased early postoperative failures or complications requiring rebubbling. The purpose of our series was to further study the feasibility and safety of nDMEK and to compare the results with traditional DMEK. This is a single center case series of 3 eyes which underwent nDMEK performed by experienced surgeons (C.P, A.M). Two eyes had nDMEK as a secondary procedure following a failed/rejected PK, while the third case underwent nDMEK on a virgin eye. Undiseased donor DM and a regular host endothelium were required to be eligible for nDMEK. The average change in CCT at last follow-up was -21.2% (±13.3). All required intracameral air injection (rebubbling) within the first few days, with a mean of 2.33 rebubblings per eye, the first one occurring at 6.33±2.52 days after surgery. Non-stripping DMEK surgery appears to be a feasible option, and results are satisfactory at mid to long term. However, in our series, the immediate postoperative period was marked by an increased rebubbling rate. While foreseeable particularly in high-risk cases, surgeons considering this technique should expect a higher risk of early rejection.

Myopic outcomes after excimer laser phototherapeutic keratectomy (PTK).

PURPOSE: To evaluate refractive outcomes following excimer laser phototherapeutic keratectomy (PTK). METHODS: A retrospective non-randomized review of refractive outcomes of 146 consecutive eyes treated with excimer laser PTK at the Rothschild Foundation, Paris, France. Inclusion criteria were all patients undergoing PTK laser using a flying spot excimer laser system (Wavelight Allegretto, Alcon Surgical, Inc.) from October 2016 to June 2018. Exclusion criteria were incomplete data, irregular astigmatism and dystrophies of uncertain diagnosis. Preoperative diagnoses included recurrent corneal erosion syndrome without dystrophy and Cogan corneal dystrophies. The primary outcome measure was the change in spherical equivalent (SEQ) at M1 post PTK. The secondary outcome measure was the creation of a regression equation for predicting refractive outcomes after PTK, by analyzing the effect of ablation depth (AD) and optical zone (OZ) diameter. RESULTS: Fifty-eight eyes of 54 patients were included. The mean OZ was 7.352 mm±0.622. The mean AD was 18.362µm±21.406. At M1 postoperatively, the mean SEQ was -2.485 D±2.628 and mean final SEQ was -1.052 D±1.260. Both OZ and AD were independent variables with significant effects on the final visual outcome. A regression equation for predicting refractive outcomes was established. No complications were observed. CONCLUSION: The Wavelight flying spot excimer laser system produces myopic outcomes following PTK. Both OZ and AD are significant variables. A regression equation was created and may aid in prediction of refractive outcomes following PTK.

[Evaluation of vision quality after laser vision correction in healthcare professionals]. / Évaluation de la qualité de vision après chirurgie réfractive au laser chez les professionnels de santé.

PURPOSE: Healthcare professionals require good quality of vision. The main objective of this study is to evaluate the satisfaction and vision quality after laser vision correction in healthcare professionals. METHODS: This is a monocentric retrospective study. An online 25-question survey was sent to ametropic physicians, surgeons and nurses who underwent corneal refractive surgery with laser-assisted in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) between July 2012 and February 2016. Questionnaire responses were recorded anonymously by the internet survey site. These patients' pre- and postoperative data were analyzed. RESULTS: In total, 2491 laser vision corrections were performed during this time frame. One hundred and fifty-eight patients were healthcare providers; 131 received the survey, and 111 responded. Ninety-nine were surgeons, 60 were medical physicians, and 32 were nurses. Ninety-one percent reported that they were satisfied with their postoperative vision quality, 63.9% even reported an improvement in their quality of vision compared with their corrected preoperative vision, 92.8% reported that they would have the procedure again, and 94.6% would recommend the procedure to a family member or a patient. Visual outcomes showed high levels of efficacy and predictability. CONCLUSION: While healthcare professionals require good quality of vision, those who had undergone laser vision correction reported the same satisfaction as the general population and would recommend the procedure to their family, friends and patients.

[Comparison of high-order optical aberrations induced by different multifocal contact lens geometries]. / Comparaison des aberrations optiques oculaires d'ordre élevé induites par différentes géométries de lentilles multifocales.

PURPOSE: To analyze the effects of different multifocal soft contact lens geometries on high-order ocular optical aberrations. MATERIALS AND METHODS: Thirty nonpresbyopic eyes were fitted with eight multifocal contact lenses: Soflens Multifocal High, Soflens Multifocal Low, Focus progressive, Acuvue Bifocal Add +2.00, Rythmic Multifocal Profile 1, Rythmic Multifocal Profile 2, Proclear D Add 2.00, Proclear N Add 2.00. All these contact lenses corrected the ametropia for far distance. The ocular aberrations were measured with and without each contact lens using a Hartmann-Shack aberrometer, (Zywave from Bausch and Lomb) successively after pupil dilation with one or two drops of Neo-Synephrine and wavefront decomposition in Zernike polynomials up to the 5th order. RESULTS: Odd and even aberrations increased for all the tested multifocal soft contact lenses. The most significant increase was noted for the a(4.0) Zernike coefficient. The mean value of a(4.0) without contact lens was -0.178+/-0.121 microm. The contact lenses having a central zone for near addition cause the inversion of the sign of the a(40) coefficient The central far vision contact lens leads to the opposite effect, increasing spherical positive aberrations. The most significant increase in total high-order ocular aberrations were noted for Proclear D soft contact lenses (0.396+/-0.109 microm without contact lens, 0.511+/-0.123 microm with contact lens; p<0.05, +29%), for Proclear N soft contact lenses (0.396+/-0.109 microm without contact lens, 0.568+/-0.165 microm with contact lens; p<0.05 +43%) and for Acuvue Bifocal soft contact lens (0.396+/-0.109 microm without contact lens, 0.567+/-0.162 microm with contact lens; p<0.05 +43%). CONCLUSION: Wearing multifocal contact lenses induces an increase in high-order ocular aberrations. The location of the near addition zone is related to the sign of the variation of the a(4.0) coefficient. The central near vision multifocal contact lenses seem to induce large amounts of negative spherical aberrations. The far vision contact lenses seem to induce an increase in positive spherical aberrations. The relative decentration of the lens to the pupil may explain the increase in odd high-order aberrations. These results might be useful to understand the visual complaints of patients fitted with multifocal contact lenses.

Determination of corneal asphericity after myopia surgery with the excimer laser: a mathematical model.

PURPOSE: To determine the theoretical change of corneal asphericity within the zone of laser ablation after a conventional myopia treatment, which conforms to Munnerlyn's paraxial formula and in which the initial corneal asphericity is not taken into consideration. METHODS: The preoperative corneal shape in cross section was modeled as a conic section of apical radius R(1) and shape factor p(1). A myopia treatment was simulated, and the equation of the postoperative corneal section within the optical zone was calculated by subtracting the ablation profile conforming to a general equation published by Munnerlyn et al. The apical radius of curvature r(2) of the postoperative profile was calculated analytically. The postoperative corneal shape was fitted by a conic section, with an apical radius equal to r(2) and a shape factor p(2) equal to the value that induced the lowest sum of horizontal residuals and the lowest sum of squared residuals. These calculations were repeated for a range of different dioptric treatments, initial shape factor values, and radii of curvature to determine the change of corneal asphericity within the optical zone of treatment. RESULTS: Analytical calculation of r(2) showed it to be independent of the initial preoperative shape factor p(1). The determination of p(2) was unambiguous, because the same value induced both the lowest sum of residuals and the lowest sum of the squared residuals. For corneas initially prolate (p(1) < 1), prolateness increased (p(2) < p(1) < 1), whereas for oblate corneas (p(1) > 1), oblateness increased (p(2) > p(1) > 1) within the treated zone after myopia treatment. This trend increased with the increasing magnitude of treatment and decreased with increasing initial apical radius of curvature R(1). CONCLUSIONS: After conventional myopic excimer laser treatment conforming to Munnerlyn's paraxial formula, the postoperative theoretical corneal asphericity can be accurately approximated by a best-fit conic section. For initially prolate corneas, there is a discrepancy between the clinically reported topographic trend to oblateness after excimer laser surgery for myopia and the results of these theoretical calculations.

Aqueous flare induced by heparin-surface-modified poly(methyl methacrylate) and acrylic lenses implanted through the same-size incision in patients with diabetes.

PURPOSE: To compare the degree of blood-aqueous barrier (BAB) breakdown in eyes of diabetic patients after phacoemulsification and implantation of heparin-surface-modified poly(methyl methacrylate) (PMMA) or soft hydrophobic acrylic intraocular lenses (IOLs) performed using the same technique with the same incision size to determine the influence of the IOLs on postoperative inflammation independent of other surgical factors. SETTING: Department of Ophthalmology, University of Paris XIII, Bobigny, France. METHODS: In a prospective study, 44 eyes of 31 diabetic patients with or without mild to moderate diabetic retinopathy were randomly assigned to receive an HSM PMMA IOL (22 eyes) or a soft hydrophobic acrylic IOL (22 eyes) after standardized phacoemulsification surgery. Both types of IOLs had a 6.0 mm optic, were inserted unfolded, and were placed in the bag through a calibrated 6.0 mm superior scleral incision. Anterior chamber flare was measured preoperatively and 1, 7, 30, and 240 days postoperatively using the Kowa 500 laser flare meter. RESULTS: The mean flare value was higher on the first postoperative day in both groups. There were no statistically significant between-group differences in flare scores or clinical parameters preoperatively or at any postoperative visit. CONCLUSIONS: No significant difference was observed in inflammation between eyes having HSM PMMA IOL implantation or those having soft hydrophobic acrylic IOL implantation through the same-size incision. This indicates that hydrophobic acrylic and HSM PMMA materials induce the same degree of BAB breakdown after phacoemulsification in eyes of diabetic patients.

[Primary congenital ectropion. Apropos of 2 cases]. / L'ectropion congénital primitif. A propos de 2 cas.

PURPOSE: Congenital lid ectropion is a rare anomaly. In the usual classification, primary ectropion caused by tightening of the anterior lamella may sometimes be confused with secondary ectropion, especially with blepharophimosis syndrome or euryblepharon. METHODS: Through analysis of two representative cases of congenital ectropion and review of literature we discuss similarities and differences between primary and secondary ectropion including blepharophimosis and euryblepharon. RESULTS: Horizontal narrowing of palpebral fissure and inversus epicanthal folds are the main clinical feature to be considered when differential diagnosis is difficult between primary forms and blepharophimosis, as ptosis is often an underlying abnormaly in both cases. CONCLUSION: To be effective, the surgical management of congenital lid ectropion requires precise clinical examination, clear understanding of causative factors and several procedures.

[Three-dimensionnal representation and descriptive geometry of the pure spherical and pure cylindrical profiles of Excimer photoablation]. / Modélisation tridimensionnelle et géométrie descriptive des profils de photoablations sphériques et cylindriques pures au laser Excimer.

PURPOSE: To analyze the theoretical shape of the lenticules of corneal tissue ablated using Excimer laser for the correction of pure negative and positive spherical and cylindrical refractive errors, and to investigate the possible correlations between their spatial configuration and the clinical outcome for each procedure. METHODS: To obtain a theoretical three-dimensional representation of each ablated lenticule, we used software that performs boolean operations on three-dimensional virtual surfaces (Bryce 3D, Metacreation, Dublin, Ireland). The representation of the theoretical shape of the refractive lenticule etched by a given profile of ablation based on a paraxial model over a circular optical zone was obtained by performing appropriate Boolean operations between different preoperative and postoperative surfaces or elements. These operations were repeated to obtain the representation of the theoretical additional lenticule corresponding to the volume of tissue ablated to blend any abrupt optical zone edges with a constant slope. RESULTS: The lenticule corresponding to the negative spherical treatment had its maximum thickness in its center and no thickness at its edge, thus inducing a natural blend with the peripheral untreated cornea. The lenticule corresponding to the positive spherical treatment had its maximal thickness at the junction between the optical and transition zones, which are both circular. The lenticule corresponding to the negative cylindrical treatment had its maximal thickness along the flatter initial meridian and an elliptical transition zone contour. The lenticule corresponding to the positive cylindrical treatment had its maximal thickness at the edge of the optical zone along the initial flatter meridian, and no thickness at the perpendicular principal meridian. The transition zone is also elliptical. CONCLUSION: The basic characteristics of the lenticule corresponding to the pure negative spherical treatment could explain the lesser degree of postoperative refractive regression than that one occurring after pure positive spherical treatment and pure positive and negative cylindrical treatments. The characteristics of the lenticules corresponding to the negative and positive cylindrical treatments may also account for the substantial spherocylindrical coupling and regression, respectively commonly observed after such treatments. The three-dimensional representation of the lenticules ablated for the correction of pure spherical and cylindrical refractive errors may help to better understand the outcome of these procedures aimed at reshaping the anterior surface of the cornea.

[A review of mathematical descriptors of corneal asphericity]. / Etude des paramètres permettant la description mathématique de l'asphéricite cornéenne.

PURPOSE: Corneal asphericity may be modeled on a conic section which can be described by the apical radius of curvature in the meridian studied and by a measure of the degree of asphericity. MATERIAL AND METHODS: Through an extensive review of the literature, we expose the principles, the population variations and report the application of such corneal modeling. RESULTS: The aspheric anterior corneal surface can be described by a conic section, defined by its radius of curvature and by a parameter measuring asphericity. We analyse the various parameters used in the literature to determine their usefulness. Conic sections, obtained by cutting a cone by a plane, include ellipses, hyperbolas and parabolas. Two useful parameters are the apical radius of the ellipse and its eccentricity defined in Cartesian terms by a second order equation where the apical radius is R and the eccentricity is e: The apical radius is that of the circle tangent to the apex of the conic section and e describes the variation of this curve with distance from the corneal apex. Baker introduced the form factor p making the equation: with It is easier to understand the effect of alteration of p than of e on corneal curvature: There is a relation between the horizontal, a, and the vertical, b, hemi-axes and R The advantage of this notation is that e(2) can be greater than 1 When p=0 the conic section is a parabola, when p<0 it is a hyperbola. Kiely et al. studied corneal asphericity by photokeratoscopy and introduced the parameter Q, where Q=p-1. Q, the asphericity factor, is used by the Eyesis and Orbscan systems; when Q=0 the cornea is spherical. Thus different parameters describe variations in corneal curvature along any meridian. Average anterior corneal asphericity using various keratometric systems is p=0.8, making the corneal section a prolate ellipse. However there is great individual variation, 20% of normals exhibiting oblate (p>1), paraboloid (p=0) or hyperbolic (p<0) corneas. all becoming more spherical with age. Little connection between asphericity and ametropia is reported, except for a tendency to flattening in myopia and towards oblateness in progressive myopia. Direct measurement of denuded cadaver corneas gave a prolate elliptical profile although calculation after deduction of epithelial thickness measured by ultrasonic biomicroscopy suggested p=-0.22, a hyperbolic profile. The few reports on the posterior surface suggest it to be hyperbolic or prolate. Increasing distance from the corneal apex worsens the comparison to a conic section as flattening increases. Precision can be improved by adding polynomial coefficients above the second degree to the equation of the section: The non-toric 3D corneal surface can be described by the following equation for the revolution of a conic section about the optic axis: x(2)+y(2)+pz(2)-2rz=0 where z is the axis of revolution. Since the mean value of p is 0.8 this corresponds to a sphere stretched along one axis, as is a rugby ball. Each meridian has the same radius of curvature and the value of p is constant. For a toric cornea the radius and value of p must be defined for two meridia at right angles. This corresponds to an elongation on an axis different from that of revolution. Similarly a toric ellipsoid is generated by rotation of an arc around an axis at right angles to its elongation. Because of its asphericity, representation of the corneal surface depends on the direction in which its curvature is measured: In the ellipsoidal model this depends on the principal meridians, the tangential, in the plane of the axis of symmetry and the saggittal, perpendicular to this. These may define two radii of curvature, the saggital (axial) and the tangential. Most algorithms assume these properties of ellipsoids. Asphericity is translated into variations in radius of curvature from apex to periphery, increasing for a flat periphery, decreasing for a steep one. Associated to toricity, it gives rise to the common butterfly pattern. Spherical aberration is minimal through a small pupil but becomes significant the larger the aperture, with deterioration of image quality. Raytracing allows analysis of the effects of non-axial rays. The mean value of Q, at -0.26 thanks to the naturally prolate asphericity of the cornea reduces spherical aberration by half. The relaxed form of the crystalline lens further reduces it by inducing the opposite spherical aberation to that of the cornea. This is important in accommodation and presbyopia. The use of an aspheric corneal surface in the schematic eye allows calculation of the ideal asphericity, which corresponds quite well with clinical findings. Radial keratotomy reverses the natural asphericity of the cornea. Photorefractive keratotomy (PRK) also changes asphericity, Q increasing to an oblate value. These changes might increase spherical aberration, explaining some postoperative deficiencies. Current excimer laser protocols ignore asphericity, relying on paraxial algorithms alone. New strategies to control asphericity in order to diminish spherical aberration may offer solutions. The original conic section models were made to improve the geometry of contact lenses. Understanding of asphericity is important in adaptation after refractive surgery. Modification of spherical aberration by contact lenses and corneal warpage induced by rigid lenses have also been studied. CONCLUSION: The approximation of the corneal surface by a conic section allows understanding of corneal asphericity and offers a quantitative description. This allows a more precise description of the corneal surface and of the genesis of certain optical aberrations of the eye.

[Early limbal autograft after alkali burn of the ocular surface]. / Autogreffe de limbe précoce après brûlure alcaline de la surface oculaire.

Limbal autograft transplantation is recommended for treatment of limbal stem cell destruction and its complications. It is appropriate to restore corneal reepithelialization and arrest corneal vascularization and scarring. In unilateral alkali injury, limbal transplantation was first recommended for late management of corneal conjunctivalization. Our patient had severe ocular unilateral alkali injury. Early autologous limbal transplant was effective in restoring an excellent corneal surface and a good visual function.