Significant Corneal Thinning Research Articles

Amniotic Membrane Transplantation in the Management of Corneal Ulceration Following Infectious Keratitis

ABSTRACT Purpose To report on the outcomes of amniotic membrane transplantation (AMT) for corneal ulceration following infectious keratitis. Method In this retrospective cohort study of 654 patients with culture-proven infectious keratitis from 8 hospitals in Galicia (Spain), a total of 43 eyes of 43 patients (6.6%) underwent AMT for postinfectious corneal ulceration. The indications for AMT were sterile persistent epithelial defects, severe corneal thinning or perforation. Results AMT was successful in 62.8% of cases, with 37.2% requiring an additional surgery. Median time to healing was 40.0 days (IQR 24.2–101.7 days) and final BCVA was lower than baseline (p = 0.001). Ulcers were large (>3 mm) in 55.8% of cases. Previous herpetic keratitis and topical steroid use were more common in patients who received AMT (p < 0.001). 49 microorganisms (43 bacteria and 6 fungi) were isolated. Conclusions AMT is a therapeutic option for complications following infectious keratitis, which present with a sterile persistent epithelial defect, significant corneal thinning or perforation.

Visual and Topographic Outcomes of Corneal Collagen Cross Linking for Post LASIK Ectasia

PurposeTo assess the topographic and visual outcomes of corneal cross-linking (CXL) for post-LASIK ectasia.MethodsA retrospective case series of patients who had progressive post-LASIK ectasia, with at least 2 years of follow-up. They had epithelium-off CXL. Topographical and visual changes were recorded.ResultsThe study included 21 eyes of 11 patients. At month 24, the final logMAR corrected distance visual acuity (CDVA) and spherical equivalent (SE) were stable compared to baseline (0.16, and −2.0 diopter (D), respectively). The final Kmean and Kmax were 42.5 and 47.4 D, respectively. Stability or improvement in CDVA, SE, and Kmax was seen in 17 eyes (81%). Significant corneal thinning was seen (438 vs 457 microns, p = 0.003). Thinning by 2% or more was seen in 12 eyes (57.1%). Failure of CXL was seen in 4 eyes (19%). No other ocular complications were seen.ConclusionCXL for post LASIK ectasia is a safe and effective modality. Despite corneal thinning, there was stability or improvement in topographic parameters and CDVA over the 2-year follow-up period.

Importance of monitoring the ocular surface of patients with Kearns‐Sayre syndrome: a case report

AbstractPurposeKearns‐Sayre Syndrome (KSS) is a congenital mitochondrial myopathy initially described by the triad: Progressive external ophthalmoplegia, pigmentary retinopathy, heart block. Surgical procedures to alleviate ptosis can cause corneal injury from exposure. The lack of blinking can lead to a difficult contraction of the muscles responsible for squeezing the meibomian glands causing their dysfunction (MGD). Therefore, the follow‐up is of special interest in those cases where we suspect KSS due to the probable appearance of complications.MethodsWe present the case of a male of 9 years old who presented a sudden‐onset ptosis and bilateral internuclear ophthalmoplegia. Initially, he was diagnosed with Myasthenia. At the age of 12, resection of the elevator upper eyelid was performed in both eyes (BE). In the successive visits: negative Bell's sign, a progressive MGD and significant corneal thinning in the lower half of the BE were observed, and the right eye (RE) was affected with an infiltrated ulcer.ResultsTreatment with high hydration in BE and RE was treated with antibiotics eye drops and antibiotic ophthalmic ointment. After reviewing the history and given the high suspicion of KSS, genetic tests were requested to confirm it. Maintenance treatment was settled in BE with high hydration, 20% autologous serum and therapeutic contact lens. After a year of exhaustive monthly follow‐up, the patient remains stable and there is no progression of the corneal thinning.ConclusionsIt is important to take care of the ocular surface in these cases of KSS due to the corneal exposure after ptosis surgery. We must achieve stability in terms of symptoms and visual acuity without incurring other complications such as infections or perforation.

Correlation between long-term use of rigid gas permeable contact lenses and endothelial morphometric changes in keratoconus patients

PurposeThis study was conducted to evaluate the effects of long-term use of rigid gas-permeable (RGP) contact lenses on corneal endothelium in keratoconus (KC) patients using non-contact specular microscopy. In addition, the correlation between wearing duration of RGP lenses (years & hours /d) and endothelial morphometric changes in KC patients was performed. This may provide more useful data for clinical application of RGP contact lens. Study designThis study was a prospective, observational, comparative, hospital based, nonrandomized, cross-sectional, and quantitative study. Subjects and methodsThe study included 40 eyes of non-wearer contact lens KC patients (group 1) and 38 KC eyes with a long history of Rose K2 RGP contact lens wearing (group 2). The corneal endothelial morphology such as endothelial cell density (ECD); coefficient of variation of cell area (CV); percentage of hexagonal cells (HEX); and central corneal thickness (CCT) were evaluated in all patients using SP3000P Specular Microscope. ResultsThe study included 40 eyes of non-wearer contact lens KC patients (20 mild KC eyes and 20 moderate KC eyes) and 38 KC eyes with a long history of RGP contact lens wearing (18 mild KC eyes and 20 moderate KC eyes). The mean duration of RGP lenses wearing was 5.67 ± 3.481 years & 12.11 ± 2.698 h/d in mild KC eyes and 7.15 ± 5.294 years &13.65 ± 2.889 h/d in moderate KC eyes. Wearing duration in hours in mild KC eyes showed a significant moderate negative correlation with ECD (r = −0.529, p = 0.024) and a moderate positive correlation with CV (r = 0.565, p = 0.015). In addition, wearing duration in years in moderate KC eyes showed a significant moderate negative correlation with ECD (r = −0.465, p = 0.039) and moderate positive correlation with CV (r = 0.627, p = 0.003). However, wearing duration in hours in moderate KC eyes showed a significant moderate negative correlation with HEX only (r = −0.490, p = 0.028). This study reported significant corneal thinning in contact lens wearer KC eyes in contrast to non-wearer KC eyes. ConclusionThis study documented a significant correlation between a long-term use of Rose K2 RGP using the three-point touch and corneal endothelial morphometric changes in KC patients. In addition, the current study confirmed a significant corneal thinning in RGP contact lens wearer compared to non-contact lens wearer KC patients. Further studies are recommended to evaluate the association between different RGP lens materials with different oxygen permeability transmissibility; different lens design types; different fitting methods; the duration of contact lens wear and the endothelial morphometric changes in KC patients.

Unilateral Traumatic Posterior Corneal Ectasia: Clinical Manifestations, Findings of Advanced Imaging, and Long-term Follow-up

PURPOSE: To describe a case of unilateral isolated traumatic posterior corneal ectasia characterized by advanced multi-modal diagnostic tests. METHODS: Case report and literature review. RESULTS: Following blunt trauma to the left eye, a 34-year-old woman presented with persistently blurry vision. Central corneal thickness was 300 µm, compared to 519 µm in the right eye. Scheimpflug tomography revealed significant corneal thinning in a defined inferotemporal region with corresponding elevation of the posterior corneal surface. Posterior corneal ectasia was confirmed with anterior segment optical coherence tomography. Wavefront aberrometry demonstrated increased higher order aberrations in the affected eye. Vision remained stable during 4.5 years of follow-up with a final visual acuity of 20/50 maintained with spectacle correction only. CONCLUSIONS: A unique case of unilateral post-traumatic posterior corneal ectasia was presented. The multi-modal imaging provided a detailed characterization of the structural characteristics of the cornea, guided management, and allowed for differentiation from other corneal pathologies at an early stage. [ Journal of Refractive Surgery Case Reports . 2021;1(2):e31–e35.]

Extreme corneal flattening following collagen crosslinking for progressive keratoconus.

To study the clinical, tomographic and densitometric features of eyes that showed >5 D of corneal flattening following collagen crosslinking (CXL) for progressive keratoconus and to identify preoperative predictive factors for such a response. This was a retrospective case control study of 548 eyes with progressive keratoconus which had undergone epithelium-off CXL (Dresden protocol) with a follow-up of 1 to 10 years. Eyes that showed ⩾5 D corneal flattening in maximum keratometry (Kmax) following CXL (group A) were compared with one eye of the remaining patients in the same cohort (group B). Changes in refraction and visual acuity, Kmax and thinnest pachymetry were compared between both groups. Univariate and multivariate regression analysis identified preoperative risk factors for unusual corneal flattening. Forty three eyes in group A were compared with 502 eyes in group B. At the time of maximum flattening, group A showed more flattening (-7.6 ± 3.2 D) and thinning (-53.7 ± 45.2 µ) than group B (-1.69 ± 2.9 D and -26.6 ± 36.7 µ, respectively). Multivariate analysis based on parameters suggested by a univariate regression analysis identified pre-op Kmax to be the most significant predictor of intense corneal flattening. A subgroup analysis of K-matched eyes revealed that the duration of time following CXL was a significant risk factor for extreme corneal flattening following CXL. An intense corneal flattening >5 D in Kmax was documented in 7.85% of a cohort of keratoconus patients who underwent CXL. High preoperative Kmax and the duration of time following CXL were significant predictors of this response which was accompanied by significant corneal thinning.

Corneal tissue properties following scleral lens wear using Scheimpflug imaging.

PurposeTo investigate the effect of short‐term scleral lens wear on the corneal stroma at a macroscopic (thickness) and microscopic (within tissue) level, including regional variations.MethodsFourteen young, healthy participants wore a rotationally symmetric, 16.5 mm diameter, scleral lens for 8 h. Scheimpflug images were captured before, and immediately after, lens wear, and also on a second day (without lens wear) to quantify natural corneal diurnal variations. After corneal segmentation, pixel intensities of the stromal tissue were statistically modelled using a Weibull probability density function from which parameters α and β were derived.ResultsBoth α and β parameters increased significantly following scleral lens wear (by 5.7 ± 10% and 6.5 ± 6.5%, respectively, both p < 0.01). Corneal thickness also increased slightly following lens wear (mean increase 0.49 ± 1.77%, p = 0.01); however, the change in α and β parameters did not correlate with the magnitude of corneal swelling. On the control day, small but significant corneal thinning was observed (−0.82 ± 1.1%, p = 0.03), while α and β parameters remained stable. Both microparameters varied significantly across the cornea, with α decreasing (−15.4 ± 0.7%) and β increasing towards the periphery (+4.4 ± 2.6%) (both p < 0.001).ConclusionCorneal microparameters α and β varied regionally across the cornea and displayed a statistically significant increase following short‐term scleral lens wear, but remained stable between morning and evening measurements taken during a control day without lens wear. These corneal microparameters may be a useful metric to quantify subclinical corneal changes associated with low level hypoxia.

COMPARATIVE STUDY BETWEEN EPITHELIUM ON AND EPITHELIUM OFF COLLAGEN CROSS LINKING WITH RIBOFLAVIN AND UVR IN TREATMENT OF EARLY KERATOCONUS

Objective: To compare the safety and efficacy epithelium on versus epithelium off collagen crosslinking with riboflavin and UVR in treatment of early keratoconus. Patients and Methods: Thepresent study was a prospective, randomized study. 40 eyes from 25 patients with a mean age of 24years (range: 15–35 years) were included. There were 15 males and 10 females, and all of themunderwent corneal CXL using riboflavin and ultraviolet-A light at the Tipa Eye Hospital, Assuit.Results: Among the included samples, 20 eyes underwent epithelium-on corneal collagen CXL, and20 eyes underwent epithelium-off corneal CXL. The incidence of postoperative pain was lowered byabout 20% in the trans-epithelial group as compared with the epithelial-off group in the first postoperative week. In addition, the incidence of postoperative corneal haze was lowered by about 50% inthe transepithelial group as compared with the epithelial-off group in the first postoperative week. Itwas also noticed that the CXL was formed in the upper-third of the corneal stroma, 20-30 μmbeneath bowman membrane in the transepithelial CXL technique, while in the classic debridementtechnique; it was formed much deeper in the stoma. In group I, after 3 and 6 months, there was anon-statistically significant corneal thinning. In group II, none statistically significant corneal thinningwas detected after 3 months, but after 6 months there was some regression in the form of cornealthinning by nearly 5-10 μm in 20% of cases. Conclusion: Both epithelium-off CXL and the epitheliumon CXL were effective in stabilizing the progression of keratoconus at least for 6 months; however,the epithelium-off CXL appeared to be much more effective in improving the refractive best-correctedvisual acuity and topographic outcomes in keratoconic eyes compared with the epithelium-on CXL.

Therapeutic penetrating keratoplasty for acanthamoeba keratitis: a review of cases, complications and predictive factors

To review 12 acanthamoeba keratitis (AK) patients who required a therapeutic penetrating keratoplasty (TPK) and determine whether there are factors at the presenting visit that can predict the need for TPK. This was a retrospective case series. All diagnosed AK patients between January, 2009 and February, 2016 at Wills Eye Hospital, Philadelphia, PA, USA, were enrolled. Information regarding demographics, disease manifestation, management and complications was collected. Potential predictors for TPK were obtained by comparing TPK cases with those who were treated medically. Sixty-three eyes from 63 patients were diagnosed with AK. Twelve eyes (19%) required TPK during the course of treatment, and 51 eyes (81%) were treated medically. Reasons for performing TPK included medically non-responsive ulcer in seven eyes (58%), perforated ulcer in three eyes (25%) and significant corneal thinning in two eyes (17%). The most common post-TPK complications included graft failure (75%), cataract (50%) and uncontrolled glaucoma required glaucoma surgery (17%). Reactivation of AK was seen in one (8%) patient. Anti-amoebic treatment beginning after 25days from the start of AK symptoms [odds ratio (OR) = 7.63; confidence interval (CI) = 1.01-55.33; p = 0.041] and poorer presenting vision (OR = 5.42; CI = 1.91-15.36; p = 0.002) were independent predictors of the need for TPK in multivariate analysis. TPK is a procedure with significant postoperative complications but is required by some patients with AK. Eyes with higher risk for needing TPK can be identified earlier and thus provided more intensive treatment and closer follow-up care.

Effects of sustained daily latanoprost application on anterior chamber anatomy and physiology in mice

Latanoprost is a common glaucoma medication. Here, we study longitudinal effects of sustained latanoprost treatment on intraocular pressure (IOP) in C57BL/6J mice, as well as two potential side-effects, changes in iris pigmentation and central corneal thickness (CCT). Male C57BL/6J mice were treated daily for 16 weeks with latanoprost. Control mice were treated on the same schedule with the preservative used with latanoprost, benzalkonium chloride (BAK), or handled, without ocular treatments. IOP and CCT were studied at pre-treatment, 2 “early” time points, and 2 “late” time points; slit-lamp analysis performed at a late time point; and expression of corneal and iridial candidate genes analyzed at the end of the experiment. Latanoprost lowered IOP short, but not long-term. Sustained application of BAK consistently resulted in significant corneal thinning, whereas sustained treatment with latanoprost resulted in smaller and less consistent changes. Neither treatment affected iris pigmentation, corneal matrix metalloprotease expression or iridial pigment-related genes expression. In summary, latanoprost initially lowered IOP in C57BL/6J mice, but became less effective with sustained treatment, likely due to physiological adaptation. These results identify a new resource for studying changes in responsiveness associated with long-term treatment with latanoprost and highlight detrimental effects of commonly used preservative BAK.

Posterior cornea and thickness changes after scleral lens wear in keratoconus patients.

To evaluate the changes in the corneal thickness, anterior chamber depth and posterior corneal curvature and aberrations after scleral lens wear in keratoconus patients with and without intrastromal corneal ring segments (ICRS). Twenty-six keratoconus subjects (36.95 ± 8.95 years) were evaluated after 8 h of scleral lens wear. The subjects were divided into two groups: those with ICRS (ICRS group) and without ICRS (KC group). The study variables evaluated before and immediately after scleral lens wear included corneal thickness evaluated in different quadrants, posterior corneal curvature at 2, 4, 6 and 8 mm of corneal diameter, posterior corneal aberrations for 4, 6 and 8 mm of pupil size and anterior chamber depth. There was a statistically significant corneal thinning (p < 0.05) in the inferior region of the KC group and in the superior region of the ICRS group. No change (p > 0.05) in the anterior chamber depth was found. The KC group showed a steepening (p < 0.05) in the temporal quadrant and a flattening that mainly affected to the superior-nasal quadrant. The ICRS group showed a steepening (p < 0.05) that mainly affected to the superior-nasal quadrant. Regarding posterior corneal aberrations, only changes (p < 0.05) in Z4 for 8 mm and Z8 for 4 mm were found in the KC group. Short-term scleral lens wear showed a thinning of the cornea and changes in the posterior corneal curvature affects different regions in keratoconus patients with and without ICRS.

An observational study of changes in corneal parameters following use of soft contact lens and rigid gas permeable lens

Background: There have been significant advancements in contact lens designs and materials over the past few decades, the lenses still represent a foreign body in the ocular environment and may lead to physiological (corneal oedema or thinning) as well as mechanical (on corneal curvature) effects on the eye.As there are not many studies reporting the effect of contact lens on eyes in Indian population, this study was designed tofill the lacunae of knowledge in this context.Aims and Objective: To evaluate and compare the change in anterior central corneal curvature &amp; central corneal thickness following use of soft contact lens (silicon-hydrogel) and Rigid Gas Permeable (fluoropolymer) contact lens.Materials and Methods: It was a Prospective, Observational, Comparative study Conducted at Venu Eye Institute &amp; Research Centre, New Delhi. Forty eyes of 21 subjects who required contact lens were included in two groups: 20 eyes in group A (RGP contact lens users) and 20 eyes in group B (Soft contact lens users). A “baseline” parameters was measured prior to contact lens use &amp; changes associated with contact lens wear was considered in relation to the normal baseline parameters when followed up at 3 and 6 months.Results: The Change in anterior central corneal curvature in both the groups was NOT statistically significant (p-value of &gt;0.05) between pre-contact lens wear and with contact lens wear at 3 &amp; 6 months. And, there was Significant Corneal thinning between pre-contact lens wear and with contact lens wear at 3 &amp; 6 months in both the groups individually (p-value &lt;0.05). However, on comparing the difference in change in CCT between both the groups was NOT statistically significant at 3 and 6 months.Conclusions: With contact lens use, there was no significant change in Anterior Central Corneal Curvature in Soft as well as RGP contact lens group at 3 &amp; 6 months. Though there was significant central corneal thinning in both the groups individually at 3 &amp; 6 months, However, on comparing the change in CCT between both the groups at 3 and 6 months was NOT significant.Asian Journal of Medical Sciences Vol.8(5) 2017 70-74

A controlled study of amniotic membrane transplantation for acute Pseudomonas keratitis

ObjectiveTo evaluate the efficacy of amniotic membrane transplantation (AMT) to improve the outcomes of acute Pseudomonas keratitis as compared with a control group. DesignProspective interventional case series with retrospective controls. ParticipantsWe studied 14 eyes with Pseudomonas keratitis as the AMT group and 11 eyes with Pseudomonas keratitis as the control group. MethodsEyes in the AMT group were treated with antibiotic therapy followed by single-layer AMT at 2 to 3 days. Eyes in the control group received only antibiotic therapy. Patients were followed for 11.1 ± 2.4 months. ResultsIn the AMT group, pain significantly decreased from a mean score of 2.4 ± 0.5 preoperatively to 1.1 ± 0.9 at day 2 postoperatively (p < 0.001). Corneal epithelial defects healed completely within 13.2 ± 2.6 days in the AMT group compared with 15.5 ± 3.4 days in the control group (p = 0.07). At final follow-up visits, the sizes of corneal opacity and deep neovascularization were not different between the 2 groups. However, the mean score for density of the corneal opacity was significantly less in the AMT group compared with the control group (2.1 ± 0.4 vs 2.5 ± 0.7, respectively, p = 0.04). Although the best corrected visual acuity using hard contact lenses was not different between the 2 groups, uncorrected visual acuity was better in the AMT group (0.45 ± 0.22 logMAR) than in the control group (0.71 ± 0.32 logMAR, p = 0.03). No patient in either group developed significant corneal thinning or perforation. ConclusionsAMT in acute Pseudomonas keratitis was associated with immediate pain relief, less density of the final corneal opacity, and better uncorrected visual acuity at the final follow-up visit.

Comparison of Corneal Thickness Measured With Optical Coherence Tomography, Ultrasonic Pachymetry, and a Scanning Slit Method

To investigate the relationship between 1310-nm optical coherence tomography (OCT), an ultrasound pachymeter, and the Orbscan II (Bausch & Lomb, Rochester, NY) in corneal thickness measurements before and after LASIK. Twenty-eight eyes of 14 patients with a mean age of 39.9 +/- 8.6 years underwent LASIK for correction of myopia with or without astigmatism. Central corneal thickness was measured with real-time 1310-nm OCT and Orbscan preoperatively and 1 day, 1 week, and 1 month postoperatively, and with an ultrasound pachymeter preoperatively and 1 month postoperatively. Measurements of corneal thickness by all instruments correlated well with one another pre- and postoperatively (r value range: 0.87 to 0.94, P<.05); however, there were significant differences among these methods (ANOVA: P<.005). Baseline readings for ultrasound and Orbscan were similar, as were readings 1 month postoperatively for OCT and Orbscan (P>.05). Thickness measured by OCT was thinner than for other instruments preoperatively (P<.005) and thicker than Orbscan postoperatively (P<.005). Significant corneal thinning (P<.001) was found with all study devices 1 day after laser ablation. Significant corneal thinning (P<.005) was found with OCT and Orbscan 1 week compared to 1 day postoperatively, and thickening (post hoc: P<.001) was evident at 1 month compared to 1 week postoperatively. Although the instruments correlated well in measuring corneal thickness after LASIK, there were significant differences. All instruments indicated corneal swelling and recovery during the first postoperative week and thickening at 1 month.

Effects of contact lenses on corneal thickness and corneal curvature during usage.

To investigate the effects of contact lenses on corneal thickness and curvature. Eighty-four eyes of 45 patients (26 female and 19 male) wearing contact lens for the first time with a median age of 23.04 +/- 7.2 years (range, 15-44 years) were included in the study. After all patients had undergone a routine ophthalmic examination, corneal thickness measurements in nine regions and corneal topography were performed before wearing contact lenses and after 1 month, 6 months, and 12 months. Patients were classified into three groups according to duration of wear. Groups were also classified into two subgroups according to the lens type (rigid gas-permeable and soft contact lenses). Mean visual acuity was 0.82 +/- 0.26 with spectacles and 0.92 +/- 0.26 with contact lenses. At the end of 1 month, statistically significant corneal thinning and thickening were noted in different regions in group 1. In group 2, statistically significant corneal thinning was noted in all regions with soft contact lenses and rigid gas-permeable contact lenses except in the inferior temporal region at the end of 6 months. In group 3, corneal thinning was noted in all regions with soft contact lenses and rigid gas-permeable contact lenses. This corneal thinning was statistically significant in all regions with the soft contact lenses except in the inferior nasal region and with rigid gas-permeable contact lenses except in the central region. When corneal curvatures were examined, corneal flattening was seen in groups 1 and 2. In group 3, corneal steepening was noted. Soft contact lenses and rigid gas-permeable contact lenses cause corneal thickening and corneal flattening in the first months, but they cause corneal thinning and corneal steepening with time. These alterations can be evaluated as evidence that contact lenses negatively influence corneal physiology.

Variability in corneal thickness before, during, and after radial keratotomy.

Precision in radial keratotomy requires accurate pachymetry for safety and efficacy. We evaluated the location, timing, and extent of changes in corneal thickness between those determined by preoperative measurement in the clinic and those determined by pre-incision and post-incision measurement in the operating room. Sixty eyes of 37 patients had ultrasonic pachymetry measurements of the central and paracentral cornea taken in the clinic 20 minutes before each patient underwent radial keratotomy. The pachymetry was repeated intraoperatively immediately before and, in a subset of 17 eyes, immediately after incisions were made, and the readings were compared. The thinnest of the four paracentral readings measured just prior to placing the radial keratotomy incisions was located temporally in 92% of the eyes and inferiorly in 8%. Corneas progressively thinned from clinic to surgery by an average of 7 +/- 12 microns centrally and 10 +/- 18 microns temporally. Additional thinning of 13 +/- 14 microns centrally and 22 +/- 23 microns temporally occurred during surgery. The thinnest paracentral corneal region measured in an eye was not always located in the same quadrant preoperatively and intraoperatively. During the time of incision placement, significant corneal thinning had occurred at each incision site. Individual variations in corneal thickness between that measured preoperatively and that measured during surgery cautions against the use of clinic readings for diamond knife settings during radial keratotomy.

Sided effects of bicarbonate on rabbit corneal endothelium in vitro

Stroma-endothelium preparations from albino rabbits were studied either in a specular microscope (and measurements made of corneal thinning under silicone oil) or mounted between two half-chambers (to permit direct measurement of endothelial fluid pump activity). Preparations were first equilibrated with bicarbonate-Ringer solutions (supplemented with glucose, adenosine and glutathione and equilibrated with 5% CO2-air). If the preparations were equilibrated with a low (2 mM) level of bicarbonate on the stromal side and variable levels (2 to 50 mM) of bicarbonate on the endothelial side, corneal thinning increased with bicarbonate concentration while fluid pump was found to be constant from 2 to 35 mM bicarbonate. In contrast, if the preparations were equilibrated with a low (2 mM) bicarbonate level on the endothelial side and 2 to 50 mM bicarbonate on the stromal aspect, corneal thinning did not occur but fluid pump declined gradually as a function of stromal bicarbonate levels. These results contrast sharply with the significant corneal thinning and fluid pump that can be measured if both sides of the preparations are equilibrated with 35 mM bicarbonate. These results further emphasise that bicarbonate ions do not simply serve to drive an endothelium-sited fluid pump in the mammalian cornea.

Corneal thickness. I. Age variation, sex difference and oculometric correlations.

An oculometric survey was performed in a Greenland Eskimo population, covering 98% of selected age groups. From this sample 839 persons without corneal abnormalities, aged 7–89 years, formed the basis of a central corneal thickness (CT) study. A sample of 98 Danes in Greenland was measured for comparison. Using Haag Streit 900 pachymeter No. I, the average of three readings from both eyes was taken to represent the individuals. In Eskimos a Gaussian distribution of CT values was found with mean and SD: 0.518 + 0.032 mm in males and 0.529 + 0.029 mm in females. A significant corneal thinning with age was seen, predominantly in males (0.0007 mm decrease per year). Thus in adults an increasingly significant sex difference was observed (0.019 mm above the age of 40), while boys and girls differed only little (0.005 mm). A subsample with primary angle‐closure glaucoma showed an insignificant CT excess.The Danes showed a corresponding thinning with age although not significant. A highly significant ethnic difference was found, but only in men (Eskimos 0.024 mm below Danes).In a subsample of 325 adult Eskimos oculometric correlations were studied. Between CT and refractive error (r = +0.12) as well as CT and anterior chamber depth (r = ‐0.12) just significant correlations were found (P &lt; 0.05). Other relationships showed weaker correlations.