Niels Ehlers

BIOMETRIC CORRELATIONS OF CORNEAL THICKNESS

Central corneal thickness, depth of anterior chamber, thickness of lens, length of vitreous, axial length, applanation (Goldmann) and indentation (Schiøtz) tension and rigidity (Friedenwald) were determined in three groups of patients; (1) 16 patients with glaucoma simplex, (2) 25 patients with ocular hypertension, and (3) 26 patients with fibrillopathia epitheliocapsularis (so‐called pseudoexfoliation of the lens). Average data and computed correlations between the parameters are given in tabular form. Corneal thickness was normal in glaucoma simplex, but significantly increased in ocular hypertension. Corneal thickness was positively correlated to applanation tension but not to indentation tension, nor to any other of the studied parameters. It is suggested that corneal thickness can be considered as a biometric parameter which yields new information about the eye not covered by the conventional parameters.

Central corneal thickness in newborns and children.

Central corneal thickness was measured optically in premature and full‐term babies, and in children. The thickness was found to decrease from the values found in premature and full‐term babies to those found in small children aged between 2–4 years. The thickness of the adult cornea is reached at the age of about 3 years.

THE THICKNESS OF THE HUMAN CORNEA AS DETERMINED BY A SPECULAR METHOD

The thickness of the human cornea was measured by a simple accurate method which entails measurement of the distance between the anterior and the posterior corneal reflections when the cornea is illuminated at an angle. As compared to methods measuring the width of the optical section, the advantage of the method is that end‐points of measurement are clearly defined, providing a better basis for an exact estimation of the corneal thickness. The optical principle of the specular method is presented in a general form. The influence of physiological variation in corneal curvature and index of refracation is analysed and shown to cause an insignificant error on the standard thickness estimate. Using this method, the corneal thickness was measured in a random population sample of 115 normal subjects, aged 10–90 years. The corneal thickness was found to approximate a normal distribution with a mean value (± SD) of 0.515 mm (± 0.033). Asignificant decrease in corneal thickness with age of 0.0045 mm per decade was found.

A TECHNICAL IMPROVEMENT OF THE HAAG-STREIT PACHOMETER Short Communication

In recent years the interest in corneal thickness has been increasing, mainly due to the appearance of the attachment I to the Haag-Streit slit-lamp, which allowed the thickness to be measured with reasonable accuracy and speed. The principle underlying this instrument is a measurement of the apparent thickness as seen at an angle of 40. Central localization on the cornea is secured by requesting the patient to look directly into the slit-beam. The thickness is thus measured along the line of sight, which is not necessarily perpendicular to the anterior corneal surface. While the posterior corneal surface is probably rather spherical, the expanding intraocular pressure tending to produce this shape, the anterior surface is more paraboloid in accordance with an increasing thickness towards the periphery. As it cannot be assumed that the anterior and posterior surfaces are exactly concentric the central corneal thickness has no unequivocal meaning. Therefore it cannot be considered erroneous to measure the thickness along the line of sight. However, this gives rise to a systematic right-left difference (left > right) increasing with the angle kappa between the line of sight and the line perpendicular to the anterior corneal surface and passing through the centre of the pupil (Ehlers & Kruse Hansen 1971). This difference is hardly

Fresh and cultured corneal grafts compared by post-operative thickness and endothelial cell density.

Thirty‐nine corneas were removed within 6 h post mortem and stored in a moist chamber at 4°C before grafting. The mean donor age was 33 years and the average time between death and grafting was 11 h. Thirty cadaver corneas were selected after trypane blue staining and cultured at 31°C for 24 h before grafting. The mean donor age was 61 years and the mean time between death and culture was 18 h. During the first 10 postoperative days fresh grafts were thinner than cultured grafts. One year after the transplantation the two groups did not differ significantly in regard to the clinical result, corneal thickness, or endothelial cell loss. This indicates that corneas from old donors with extended post mortem time can be used for transplantation after individual evaluation and corneal culture.

LONG TERM RESULTS OF CORNEAL GRAFTING IN KERATOCONUS

Fifty‐four corneal grafts in 45 keratoconus patients have been followed for 3 to 12 years (average 5.8 years). The corneal clarity, visual acuity, incidence of immune rejections, relation to HLA compatibility, corneal thickness and endothelial cell density are reported. At the follow‐up 98% (53 out of 54) of the grafts were clear. Visual acuity was ≥ 0.67 in 72% of the cases. Suboptimal vision was due to cataract or large astigmatism. Rejection had occurred in 5 cases (10%). The graft thickness was found to decrease steadily, reaching subnormal values about 1/2 year after the operation. Six years after grafting, however, the thickness did not differ from that of normal corneas. The endothelial cell density in uncomplicated cases ranged from 450 to 3000 cells/mm2, decreasing with length of post‐operative period. The HLA compatibility could not be shown to influence the endothelial cell density.

Corneal transplantation using long-term cultured donor material.

Abstract Twenty‐seven corneal transplantations with a mean duration of donor incubation of 14.3 days (group 1) and 36 transplantations with a mean duration of incubation of 29.8 days (group 2) were followed for 18 months. No significant difference was found in graft survival between the two groups (81 versus 80%). Almost all graft failures were found among pre‐operatively defined high‐risk cases, i.e. previously transplantated and/or vascularized recipient cornea. The profile of the corneal thickness curve was almost identical in the two groups, and normal values were reached in both. Visual acuity was 0.5 or better in 23% of the cases in group 1, and 35% in group 2. These figures were highly influenced by co‐existing and complicating eye disease i.e. amblyopia, cataract, macular degeneration and glaucoma. The results show that 2 weeks and 4 weeks cultured cornea do not differ with respect to graft survival and thickness. The over all results indicate that long‐term cultured donor material is suitable for corneal transplantation and fully comparable to material stored by other methods.

Corneal transplantation and HLA histocompatibility. A preliminary communication.

A series of 222 cases of 7 mm penetrating corneal grafts were analysed with respect to the influence of HLA compatibility. The degree of compatibility was random as no matching was done (HLA types unknown at time of operation). Consequently, most of the cases showed 3 or 4 incompatibilities.

CENTRAL THICKNESS IN CORNEAL DISORDERS

In the single individual the central corneal thickness (CCT) shows only small variations. Therefore CCT has been studied in a number of corneal diseases in order to investigate if this dimension might contribute to the diagnosis or to the understanding of the pathogenesis.

Bullous keratopathy (Fuchs' endothelial dystrophy) treated systemically with 4-trans-amino-cyclohexano-carboxylic acid.

Twenty patients with bullous keratopathy (Fuchs endothelial dystrophy) were treated systemically with the antifibrinolytic drug tranexamic acid. The effect was evaluated by slit‐lamp biomicroscopy, measurement of central corneal thickness and determination of visual acuity. The patients subjective complaints were also registered. The duration of the treatment varied from 3 to 16 months. In most cases the treatment was given over several periods with intervening free intervals.