Increase In Corneal Thickness Research Articles

Corneal thickness and endothelial density before and after cataract surgery

BACKGROUND/AIMSDeturgescence of the corneal stroma is controlled by the pumping action of the endothelial layer and can be monitored by measurement of central corneal thickness (pachymetry). Loss or damage of...

Intraocular pressure development in the rabbit eye after aqueous exchange with ophthalmic viscosurgical devices

Purpose To evaluate an animal model used to study intraocular pressure (IOP) development after aqueous exchange with several commercially available ophthalmic viscosurgical devices (OVDs). Setting Department of Preclinical Ophthalmology, Pharmacia & Upjohn, Uppsala, Sweden. Methods Albino rabbits (New Zealand White) were used. Aqueous humor (50 μL) was exchanged with 8 OVDs. The IOP was measured every second hour for 12 hours and then 24, 48, and 72 hours after aqueous exchange using a pneumotonometer (Modular One, Bio-Rad Digilab Inc). A minimum of 7 eyes was used for each OVD. Healon® was used as control in 1 eye in all experiments. The OVDs were Viscoat® (chondroitin sulfate–sodium hyaluronate), Provisc® (sodium hyaluronate), Biolon® (sodium hyaluronate), Healon GV®, Healon®5, Ophthalin® (sodium hyaluronate), Ocucoat® (hydroxypropyl methylcellulose), and Ivisc® (sodium hyaluronate). Results All OVDs caused a postoperative increase in IOP. At 24 hours, the IOP was at the preoperative levels. However, there was considerable variation in the maximum IOP value and when this value occurred. The maximum value appeared to depend on the concentration of the rheologically active substance in the product and the time of the average molecular mass. There was also an increase in central corneal thickness, with a maximum increase 24 hours after the exchange but a large variation among animals. Conclusion The animal model appears to be useful for comparing various OVDs, and the results may serve as a guide for the design of clinical studies of new products.

Normal-tension glaucoma and central corneal thickness.

To determine whether a decreased corneal thickness is a primary factor in the lower intraocular pressure readings found in normal-tension glaucoma patients. Fourteen patients with normal-tension glaucoma were compared with 14 age- and sex-matched glaucoma patients. Corneal thickness was measured by ultrasonic pachymetry on each eye. The corneal thickness (mean +/- SD) in patients with normal-tension glaucoma was 0.536 +/- 0.035 mm. The corneal thickness in patients with glaucoma was 0.537 +/- 0.035 mm. The 95% confidence interval for the difference between the two groups was -0.027 to +0.027 mm. It has been documented that increased corneal thickness leads to high readings of intraocular pressure. Therefore, decreased corneal thickness may lead to a lower intraocular pressure reading. This study suggests that for most normal-tension glaucoma patients corneal thickness is not a major factor in accounting for the lower intraocular pressure measurements when compared with primary open angle glaucoma patients.

Erbium laser phacoemulsification--a clinical pilot study

From August 1997 to March 1998, we performed a prospective pilot study to examine erbium laser phacoemulsification in cataract surgery under clinical conditions and to determine the side effects of this method. 34 patients (40 eyes) with senile cataract were recruited. Slit lamp findings, keratometry, best corrected visual acuity, refraction, pachymetry, endothelial cell count and intraocular pressure were determined preoperatively and on 1st, 4th, 14th and 60th postop day according to a standardised protocol (single pulse energy between 10 and 20 mJ, frequency of application 60 Hz, average phaco time 3 min, total energy 38.5 mJ). The operations were done with the erbium laser system MCL 29, Aesculap-Meditec Co., Jena, Germany. A total emulsification of the nucleus was possible in 36 of 40 eyes (90%) (nucleus hardness between 0 and 3). A partial emulsification of the nucleus in nucleus hardness 3 was possible in 2 eyes, in nucleus hardness 4 in 1 eye and in nucleus hardness 2 in 1 eye (4 eyes--10%). Visual acuity increased from 0.3 preop to 0.8 two months postop (median). Intraocular pressure decreased from 16 mm Hg preoperatively to 13 mm Hg two months postoperatively (median). The increase of corneal thickness was not statistically significant compared to baseline. The decrease of endothelial cell count was 0.96%. Postoperative complications which are not known in ultrasonic phacoemulsification did not appear in erbium laser phacoemulsification. Erbium laser phacoemulsification is a surgical method that makes the emulsification of softer nuclei under clinical conditions possible with a low rate of complications also in the beginning of the learning curve. For higher nucleus hardnesses, technical and surgical parameters have to be optimised. Advantages of erbium laser phacoemulsification compared to ultrasonic phacoemulsification are less energy transmission into the eye, no heating of anterior chamber, impossibility of corneal burns and easier access in eyes that are deep into the orbit. Especially advantageous is the high protection of endothelium by erbium laser phacoemulsification. A prospective controlled comparative study to ultrasonic emulsification is desirable.

Effects of hypoxia on corneal epithelial permeability

PURPOSE: Epithelial permeability to fluorescein (Pdc) increases with closed-eye soft contact lens wear. Possible mechanisms responsible for this change include corneal hypoxia (and acidosis) during overnight wear and interference of the lens with normal tear exchange. In this study we used a local environmental chamber to examine the effects of hypoxia on Pdc.METHODS: After baseline slit-lamp examination, autofluorescence, and central corneal thickness measurements, 35 subjects were fitted with a pair of airtight swimming goggles. One eye was exposed to a humidified gas mixture containing 95% nitrogen (N2) and 5% carbon dioxide (CO2), and the fellow (control) eye was exposed to air. The experimental eye and the eye measured first were assigned using a randomized block design. After the subjects wore the goggles for 1 hour, corneal thickness measurements were repeated and Pdc was assessed as previously described. A final slit-lamp examination was performed by a masked examiner to assess epithelial integrity.RESULTS: There was no significant difference in the mean ln(Pdc) (95% confidence interval) for eyes exposed to N2/CO2 when compared with paired eyes exposed to air (−2.70 [−2.99, −2.41] vs −2.51 [−2.72, −2.30] ln[nm/sec], P = .272). Although there was also no substantial difference in the slit-lamp appearance of the experimental and control eyes, the mean (95% confidence interval) change in corneal thickness for the hypoxic eyes was 19.78 (15.72, 23.84) μm compared with 3.40 (−0.67, 7.47) μm (P < .0001) in the control eyes.CONCLUSION: One hour of hypoxia caused a significant increase in corneal thickness with no apparent change in Pdc. This suggests that other factors, either alone or in combination with hypoxia, may be responsible for increased Pdc during closed-eye contact lens wear.

Effects of experimental exposure to triethylamine on vision and the eye.

OBJECTIVES: To determine the effect of triethylamine (TEA) on the cornea and to evaluate the cause of blurred vision. To find the lowest observed effect concentration of exposure to TEA....

Acute corneal decompensation after silicone oil removal.

To assess acute corneal decompensation after silicone oil removal in some aphakic eyes with clear corneas whose anterior chambers were completely filled with silicone oil for a considerable period of time. Eight eyes of 8 patients who underwent vitrectomy and intraocular silicone oil injection were studied. All the eyes were aphakic and anterior chambers were completely filled with silicone oil. In all eyes, corneas were clear and no corneal finding indicating keratopathy was detected by slit-lamp microscopy before silicone oil removal. The mean silicone oil removal time was 4 months (range 2-7 months). A specular microscope was used for the evaluation of corneal endothelial changes and corneal pachometry was performed to observe corneal changes before and after the silicone oil removal in 5 eyes besides slit-lamp microscopy. The follow up period after silicone oil removal was 2-12 months (mean 6 months). In all eyes severe corneal stromal edema and clouding was detected in the first day following silicone oil removal. Increased corneal thickness was seen in all eyes. Decreased (at or below critical levels) corneal cell density was detected by specular microscopy before and after silicone oil removal. No significant improvement was observed during the follow up period. Eyes whose anterior chambers completely filled with silicone oil could be evaluated as clear corneas by slit lamp microscopy despite severe endothelial damage. We recommend that eyes with silicone oil in the anterior chambers should be monitored by a combination of slit-lamp microscopic examination and specular microscopy to determine the relative corneal endothelial tolerance to the silicone oil and endothelial damage. Early removal of the silicone oil can be considered when the retinal adhesion allows.

Regression and its mechanisms after laser in situ keratomileusis in moderate and high myopia

Objective The purpose of the study was to evaluate the degree and mechanism of regression after laser in situ keratomileusis (LASIK) on moderate to highly myopic eyes during the first postoperative year. Design A prospective, single-center, clinical trial. Participants A total of 52 eyes of 38 patients were entered in the study; 47 eyes had complete data available at each postoperative visit. Intervention The intervention was LASIK using the microkeratome to create an 8.5- to 9.0-mm diameter, 130- to 160-μm-thick flap. A spherical midstromal multizone ablation (inner zone, 4.5 mm; outer zone, 5.5–6.0 mm) was then performed using the Summit OmniMed excimer laser (Summit Technology, Inc, Waltham, MA). The mean preoperative refraction was −14.02 diopters (D). Retreatment for undercorrection and regression was performed between postoperative months 3 and 6 on 13 eyes. Main outcome measures Manifest spherical equivalent, mean central corneal power, and central corneal thickness were the parameters measured. Results At 3 months, follow-up data were available on 47 eyes. The mean refractive regression was −1.07 D (7.6%) from the first week to the third month. During the first postoperative year, the mean regression of manifest spherical equivalent (MSE), increase in corneal power, and increase in corneal thickness were symmetric in magnitude and time course for the 34 eyes that did not require retreatment (−0.96 D, +1.03 D, and 15 μm, respectively). Conclusion Early regression of refractive effect after LASIK appears to be a consequence of an increase in corneal thickness associated with central corneal steepening. No evidence of progressive corneal ectasia was observed during the first year of follow-up. Longer follow-up is required to confirm these trends.

A morphological and functional study of Congenital Hereditary Endothelial Dystrophy.

To contribute to the basic understanding of Congenital Hereditary Endothelial Dystrophy (CHED) by clinical, functional, and histopathological examinations of three cases. Prior to grafting, corneas were evaluated by slit lamp examination and by assessment of endothelial permeability to fluorescein. Following penetrating keratoplasty, corneal buttons were evaluated by light- and electron microscopy and by assessment of stromal swelling pressure. Patients with CHED had a markedly increased corneal thickness (0.93-0.98 mm) with epithelial oedema and a stromal swelling pressure close to zero; suggesting that the stroma was maximally swollen in vivo. Corneal endothelium showed an increased permeability to fluorescein; suggesting a functional barrier defect. Histopathological evaluation revealed: 1) a normal endothelial cell density; 2) an abnormal endothelial morphology with irregular and multi-nucleated cells containing abnormal cell organelles; and 3) a profound thickening of Descemet's membrane, 16-18 microm, with multiple focal areas of abnormal fibrillar deposits in the posterior half. This study suggests that the primary defect in patients with CHED is a degenerated and dysfunctional corneal endothelium, characterized by an increased permeability and an abnormal and accelerated Descemet's membrane secretion. The underlying pathophysiological mechanism(s) may be related to an abnormal endothelial barrier function, leading to secondary swelling of the stroma and epithelium. Further studies are needed to identify the specific functional defect(s) and the embryological origin of the abnormal corneal endothelium in CHED.

Regulation of fluid flow through corneal stroma in the bullfrog

Regulation of fluid flow through corneal stroma was investigated in the bullfrog. Corneal specimens were mounted by clamping their limbal sciera between the two chambers of a Ussing-type chamber. The epithelial surface was covered with Ringer's solution, while the endothelial surface was superfused with Ringer's solution at various pressures ranging from 0–60 mm Hg. At 0 mm Hg, the cornea swelled, while at 10 mm Hg the corneal thickness remained unchanged. Further elevation of the hydrostatic pressure of the endothelial superfusion solution caused a decrease in corneal thickness, suggesting that the hydrostatic pressure in the in vivo frog corneal stroma is about 10 mm Hg. At 10 mm Hg of endothelial superfusion pressure, piercing the epithelial cell layer with a 30-gauge needle caused only slight corneal swelling. Removing glucose from the epithelial perfusion solution induced a slowly progressing increase in corneal thickness. Iodoacetate did not interfere with the swelling of the pierced cornea after the removal of glucose from the epithelial perfusion solution. To examine the possibility that the interstitial fluid flows across the stroma-scleral boundary, corneal specimens having undamped sclera were incubated in Ringer's solution containing 3 mmol/L dextran of various molecular weights ranging from 8800–162000, and the volume of the preparation was monitored by sequential measurement of the weight. In the presence of dextran with a molecular weight higher than 70000, the corneal volume decreased at the beginning of incubation, and after reaching the minimal volume it slowly increased, indicating that the stroma-scleral boundary is permeable to dextran of even a molecular weight of 162000, although dextran molecules diffuse much more slowly than water, and the concentration of unfilterable solutes in the stroma is lower than 3 mmol/L. In experiments using the Ussing-type chamber at 10 mm Hg of endothelial superfusion pressure, a decrease of NaCl in the superfusing solution to 1/2 caused rapid corneal swelling followed by slow recovery. Adding NaCl to the 1/2 NaCl Ringer's solution caused a further corneal thinning in a concentration-dependent manner. The same extent of decrease in corneal thickness as induced by adding NaCl was achieved by the same concentration of glucose as of NaCl, implying that the value of the reflection coefficient of the endothelial cell layer to either Na + or Cl − is about half that of glucose. Our results show that even a small difference in the concentration of low molecular weight solutes (e.g., Na + and Cl −) exerts a force that draws water from the cornea.

Corneal Endothelial Toxicity of Topical Anesthesia

To determine the relative corneal endothelial toxicities of the following topical anesthetic agents: bupivacaine HCl 0.75%, unpreserved lidocaine HCl 4%, proparacaine HCl 0.5%, and tetracaine HCl 0.5%. The experiment was conducted using pigmented rabbits. Approximately nine animals each were randomly assigned to eight groups. Right eyes received injections of 0.2 ml of one of the four anesthetic agents at one of two concentrations and left eyes received injections of 0.2 ml of balanced salt solution. Corneal thickness and clarity were measured before surgery and on postoperative days 1, 3, and 7. A statistically significant increase (P < 0.05) in corneal thickness and opacification over preoperative measurements was noted with injections of bupivacaine, lidocaine, and proparacaine, controlling for changes occurring in control eyes from surgery alone. Proparacaine was statistically more toxic than were the others. The toxicity of tetracaine was statistically indistinguishable from balanced salt solution, although mild toxicity was evident clinically. Injection of 1:10 dilutions of the same anesthetic agents failed to produce a statistically significant increase in corneal thickness or opacification on any postoperative examination. Anterior chamber injection of bupivacaine HCl 0.75%, unpreserved lidocaine HCl 4%, and proparacaine HCl 0.5% produces corneal thickening and opacification that is clinically and statistically significant. Tetracaine HCl 0.5% injection produces corneal thickening and opacification that is clinically apparent in some eyes but statistically insignificant. Ophthalmic surgeons should be aware of the potential for endothelial cell injury if anesthetic agents enter or are injected into the eye during cataract surgery in the concentrations supplied commercially.

Corneal endothelial changes after divide and conquer versus chip and flip phacoemulsification

Purpose: To evaluate changes in central corneal endothelial cells and corneal thickness after divide and conquer phacoemulsification and chip and flip phacoemulsification.Setting: Houston Eye Clinic, Houston, Texas, USA.Methods: Forty-four eyes were randomly assigned to one of two groups to have divide and conquer (D/C Group) or chip and flip (C/F Group) phacoemulsification with implantation of a posterior chamber, foldable, silicone intraocular lens performed by one surgeon. Of these, 41 eyes of 37 patients (22 D/C Group, 19 C/F Group) met the inclusion criteria. All surgeries were uneventful. A complete eye examination including specular microscopy and pachymetry was performed preoperatively and 1 week and 1 and 3 months postoperatively.Results: There were no significant between-group differences in any of the following means: sex; age; time at 70% phaco power; total phacoemulsification time. No correlation was found between ultrasound time and increased corneal thickness except for a significant increase in percentage of hexagonal cells in the C/F Group at 1 month. The only statistically significant between-group differences were greater endothelial cell loss in the C/F Group at 1 month and the percentage change in hexagonal cells at 1 week (1.1 % increase, D/C Group; 10.7% decrease, C/F Group).Conclusion: The divide and conquer technique led to less endothelial loss and hexagonal cell change than the chip and flip technique, although at 3 months the differences were not significant.

Distribution of Central Corneal Thickness and Its Association With Intraocular Pressure: The Rotterdam Study

To perform a cross-sectional study on the distribution of central corneal thickness and its association with intraocular pressure in an elderly population. We measured central corneal thickness and intraocular pressure in 395 subjects (352 control subjects, 13 patients with ocular hypertension, and 30 patients with primary open-angle glaucoma) aged 55 years or more. Mean central corneal thickness in the 352 control subjects was 537.4 microm (95% confidence interval [CI], 533.8 to 540.9 microm; range, 427 to 620 microm), with a maximal difference between eyes of 42 microm. There were no differences between sexes and no significant association with age. Linear regression analysis showed an increase of 0.19 mm Hg in intraocular pressure with each 10-microm increase in central corneal thickness (95% CI, 0.09 to 0.28 mm Hg). This association was similar in both eyes and in both sexes. The 13 patients with ocular hypertension had corneas a mean of 16.0 microm thicker (95% CI, -2.6 to +34.6 microm) compared with control subjects (P = .093); the 30 patients with primary open-angle glaucoma had corneas a mean of 21.5 microm thinner (95% CI, 8.8 to 34.1 microm) compared with control subjects (P = .001). Mean central corneal thickness was similar to that found in clinical studies, was slightly higher in patients with ocular hypertension, and was significantly lower in patients with primary open-angle glaucoma. Intraocular pressure was positively related with central corneal thickness. Central corneal thickness may influence the division between normal and increased intraocular pressure at a simple cutoff point of 21 mm Hg.

Laser in situ keratomileusis to correct high myopia

Purpose: To evaluate the effectiveness, predictability, and safety of laser in situ keratomileusis (LASIK) in 143 eyes with myopia from 8.00 to 20.00 diopters (D).Setting: Alicante Institute of Ophthalmology, University of Alicante School of Medicine, Alicante, Spain.Methods: This prospective study comprised 143 eyes (94 patients) that had LASIK with the Chiron Automated Corneal Shaper and the VISX 20/20 excimer laser using a multizone profile and a sutureless hinged corneal flap technique.Results: Uncorrected visual acuity was 20/40 or better in 45.0% of eyes 3 months postoperatively and in 46.4% at 6 months. Best corrected visual acuity (BCVA) improved by 0.07 at 3 and 6 months and was stable after 3 months. Mean spherical equivalent was -13.19 diopters (D) ± 2.89 (SD) preoperatively and +0.51 ± 1.63 D at 3 months and +0.18 ± 1.66 D at 6 months postoperatively. At 3 months, spherical equivalent was within 1.00 D of emmetropia in 57.5% of all eyes, 71.0% of eyes with a baseline refraction from -8.00 to -11.99 D (n = 59), 44.4% with a baseline refraction from -12.00 to -15.99 D (n = 54), and 53.0% of eyes with a baseline refraction from -16.00 to -20.00 D (n = 30). The respective 6 month percentages were 60.0, 72.4, 46.0, and 50.0%. The regression of effect was similar in all groups (approximately 0.50 D) between 1 and 3 months, although the high myopia group had further regression. Significant corneal steepening and an increase in corneal thickness occurred between 1 and 3 months. Flap thickness was always less than predicted with both the 130 and 160 μm plates, and achieved laser ablation was deeper than programmed. The relationships between postoperative refraction and preoperative keratometry and postoperative refraction and the difference in achieved versus programmed ablation were significant. Complications at 6 months included epithelial ingrowth, corneal flap melting, decentered ablation, and irregular astigmatism with loss of BCVA, although none was vision threatening.Conclusion: In this study, LASIK was effective and predictable in the correction of high myopia but was more accurate for myopia up to 12.00 D. Current surgical algorithms must be modified to improve predictability in higher corrections. Longer follow-up is necessary to evaluate long-term incidence of vision-threatening complications.

Corneal endothelial protection by different viscoelastics during phacoemulsification

Purpose: To evaluate corneal endothelium morphology and function after phacoemulsification using different viscoelastics.Setting: Eye Clinic, University of Trieste, Italy.Methods: This prospective, randomized study included results of preoperative and postoperative (7, 30, and 90 days) examinations of 66 patients scheduled for phacoemulsification without other ocular pathology; 8 patients were excluded. Patients were randomly assigned to one of four groups based on type of viscoelastic used: 1% sodium hyaluronate (Healon®); 1.4% sodium hyaluronate (Healon GV®); 4% sodium chondroitin sulfate-3% sodium hyaluronate (Viscoat®); 2% hydroxypropyl methylcellulose (Hymecel®). Mean cell density and cell size variation coefficient were determined by specular microscopy; central corneal thickness, by ultrasonic pachymetry; and endothelial permeability coefficient and active pump function, by anterior segment fluorophotometry.Results: There were no significant differences in postoperative mean cell loss among the groups. The cell size variation coefficient was altered in all groups 7 days after surgery and was still impaired at 30 days in the Hymecel group. A significant increase in mean corneal thickness, endothelial permeability, and active pump function occurred in the Healon and Hymecel groups 7 days after surgery. These parameters were still altered 30 days after surgery in the Hymecel group. Endothelial functional alterations did not occur in the Healon GV or Viscoat group.Conclusion: Viscoat and Healon GV are effective in minimizing functional damage of endothelial structure in the early and medium-term postoperative period.

Corneal Thickness Changes Following Exposure of New Zealand White Rabbits to Bis [2-(Dimethylamino) Ethyl] Ether Vapor

Bis[2-(dimethylamino)ethyl]ether (CAS No. 3033-62-3; DMAEE) is a liquid industrial chemical whose vapor causes glaucopsia, a transient blue-gray haziness of vision, in exposed workers. The possible role of increased corneal thickness as a basis for the visual disturbances was investigated in groups of five female New Zealand White rabbits exposed for 2 h to mean analytically measured concentrations of DMAEE vapor of 0.1, 0.9, 4.6, 8.8,12.2,14.9, 21.1, and 24.8 ppm; a control group was exposed to air alone. Corneal thickness was measured by an ultrasonic pachymeter before and immediately following exposure and at approximately 30 min, 3, 5, 24, 48, and 72 h postexposure, and thereafter as necessary. Eyes were inspected for signs of conjunctival and corneal inflammation and injury at 30 min; 3,24, and 48 h; at 7 days or longer as considered necessary. No conjunctivalirritation or corneal dullness was seen at 0.1 or 0.9 ppm DMAEE vapor, but at 4.6 ppm and above, exposure-related conjunctivitis and corneal dullness occurred with no clear dose-response relationship. Corneal thickness was slightly, although not statistically significantly increased at 4.6 ppm, and not until about 48 h postexposure. At 8.8 ppm and above increases in corneal thickness were measured immediately postexposure and generally in an exposure concentration-related manner, with a maximum at 3 h and slightly increased throughout the evaluation period. Peak increases occurred with 21.1 ppm (23.7% at 3 h). The results accord with DMAEE-induced glaucopsia being the result of transient increased corneal thickness. The no-effects concentration for induced corneal cloudiness was between 0.9 and 4.6 ppm DMAEE vapor, and for objectively assessed increased corneal thickness, between 4.6 and 8.8 ppm.

Diurnal variations in human corneal thickness.

To elucidate the diurnal variation in human corneal thickness over a 48 hour period. Changes in central corneal thickness were monitored in eight healthy subjects (four male, four female) aged between 10 and 63 years using an ultrasonic pachymeter. Measurements were made over a 48 hour period-immediately before sleep, immediately upon waking and at 15, 30, 45 minutes, 1, 1.5, 2, 2.5, 3 hours, and at 2 hour intervals thereafter throughout the remainder of each day. The mean corneal thickness for the group (SD) was 546 (14) microns, with a mean overnight increase of 5.5% (2.9%) (range 1.9-12.6%) and a maximum diurnal increase of 7.2% (2.8%) (range 2.1-14.3%). Individual differences in the extent of diurnal and overnight variation occurred within the group. For three subjects, the first reading taken on waking was not the highest and corneal thickness continued to increase. These data confirm an increase of corneal thickness during sleep, but also reveal considerable variation during waking hours. Thus, the overnight changes in corneal thickness are not truly representative of diurnal variations in human corneal thickness and, in fact, much greater diurnal variation occurs than the 3.0-4.4% previously reported.

Anterior stromal punctures for bullous keratopathy.

To evaluate the therapeutic effects of anterior stromal punctures (ASP) in patients with bullous keratopathy (BK). Twenty-seven patients awaiting penetrating keratoplasty with a diagnosis of BK were examined. They were seen before treatment with ASP and 1, 4, and 12 weeks after treatment. The examination included slit-lamp examination, photography of the cornea, ultrasonic pachymetry, central esthesiometry, and pneumotonometry. Subjective evaluations of pain, discomfort, and photophobia were also done using a visual scale model. Photographs were analyzed by computer-assisted planimetry and used to measure the corneal surface covered by bullae and microcysts. Pretreatment and posttreatment values (mean +/- SEM) were compared using the Student paired t test. At 3 months, a significant reduction in pain was noted. A decrease in the mean corneal surface covered by bullae (BKPreASP = 2733 +/- 553 microns2; BK3mo = 1006 +/- 356 microns2, P = .004) was observed. A decrease in the esthesiometry (E) measurement (EPreASP = 3.5 +/- 0.4 cm; E3mo = 1.3 +/- 0.3 cm, P < .001), an increase in corneal thickness ([CT] CTPreASP = 869 +/- 24 microns; CT3mo = 902 +/- 21 microns, P < .001), and a decrease in the number of quadrants through which iris (I) details could be seen (IPreASP = 1.7 +/- 0.3; I3mo = 1.2 +/- 0.3, P = .015) were also noted. These findings corroborate the clinical observation of increased subepithelial fibrosis following ASP. Anterior stromal punctures reduce bullae formation and alleviate pain in patients with BK, and they constitute a valuable alternative to penetrating keratoplasty should surgery be delayed or contraindicated.

Structure and function of the corneal endothelium in diabetes mellitus type I and type II.

To measure and compare corneal endothelial morphologic characteristics and function in subjects with diabetes mellitus types I and II. Forty-nine patients with diabetes mellitus type I and 60 patients with diabetes mellitus type II were recruited from the active practice of the Mayo Clinic, Rochester, Minn. Thirty-one normal subjects, divided by age into two overlapping groups of 20 each, served as controls. Corneal endothelial permeability and corneal autofluorescence were measured by fluorophotometry. Central corneal endothelial photographs were taken with a wide-field specular microscope, which also measured the corneal thickness. Neither the type I nor the type II diabetics differed from their controls in endothelial permeability and endothelial cell density. The type I diabetics had polymegethism, pleomorphism, increased corneal thickness, and increased corneal autofluorescence compared with their controls. Similar measured values were found in the type II diabetics, but they did not differ significantly from those of their age-matched controls. The type II diabetics were older than the type I diabetics, and the older control group showed changes similar to those seen in the diabetics; these changes were presumably associated with aging. The severity of retinopathy was significantly correlated only with corneal autofluorescence. The corneas of patients with type I diabetes mellitus exhibit abnormalities in endothelial cell morphologic characteristics and corneal autofluorescence. The changes resemble those that occur with aging in normal subjects, making them difficult to discern as abnormal in type II diabetics, who are usually older. We found no abnormalities in endothelial permeability in either type I or type II diabetics.

Ocular Hypertension and Central Corneal Thickness

Purpose: To determine whether ocular hypertension (OHT) is over diagnosed in patients with increased corneal thickness.Methods: Thirty-six patients with OHT were compared with 29 control subjects and 31 patients with glaucoma. Corneal thickness was determined by ultrasonic pachymetry and measured at a single point, 1.5 mm temporal to the corneal light reflex.Results: The corneal thickness (mean ± standard deviation) in patients with OHT was 0.610 ± 0.033 mm. This was significantly greater than in patients with glaucoma (0.557 ± 0.039 mm) and control subjects (0.567 ± 0.036 mm).Conclusion: It is well documented that increased corneal thickness leads to artificially high estimations of intraocular pressure. This study confirms that a significant number of patients with OHT have a normal intraocular pressure if corneal thickness is taken into account. Corneal pachymetry is clinically helpful in estimating intraocular pressure, determining the risk of visual loss, and establishing a target pressure.