|Year : 1983 | Volume
| Issue : 7 | Page : 1040-1042
Pachometry in Indian subjects
V Kalevar, S Bhatia
Gita Bhawan Hospital Indore, India
Gita Bhawan Hospital, Indore
|How to cite this article:|
Kalevar V, Bhatia S. Pachometry in Indian subjects. Indian J Ophthalmol 1983;31:1040-2
Pachometer or depth measuring device is an accessory for a modern slit lamp for measuring the actual thickness of transparent media of the eye ball.
Two different attachments are available. Pachometer-I measures thickness upto 1.2 mm and is suitable for measuring the corneal thickness which is of particular importance in many corneal pathologies where stromal swelling is a significant clinical feature. A record of actual thickness in fractional millimeters helps assess progress of disease as well as effectiveness of therapy.
Pachometer-II measures thickness upto 6 mm and is therefore used for measuring anterior chamber depth and antero-posterior axis of lens.
Of the two P-I is of far greater clinical value.
The principle of Pachometry is to split the optical section in upper and lower halves and then focus them so as to coincide the measuring points, described later.
Each of the attachments consists of a fixation base, a measuring device, a split image eye piece and a corrective table. The fixation base and split image eye piece are common for both, P-I and P-II. The measuring device is separate and has to be interchanged if after corneal thickness, depth of ant. chamber or lens thickness is to be maeasured.
| Material and methods|| |
The Pachometer is mounted on the fixation base screwed on the binocular microscope of slit lamp. The illumination arm of slit lamp is on the left side of the observer and is so adjusted that the light passes through the vertical slit of the diaphragm on the measuring device and falls on the cornea.
The right eye piece of binocular microscope is exchanged with the Split-image eye piece which contains a base to base prism oculus. The line of separation must be adjusted in a perfect horizontal position.
A +2.5 Dioptre correction is added to the normal setting of the observer on the right eye piece for P-I and +6.0 Dioptre for P-II.
Other adjustments of the slit lamp are as for routine biomicroscopy.
Illumination is adjusted to the brightest. Slit width is smallest to get a thin sharp biosection. Observation is uniocular through the right eye piece only. The illuminated slit appears in two halves, upper and lower, separated by a horizontal line. The measuring scale is adjusted at zero. The focussed beam of light now appears in perfect alignment. The scale is moved from zero to a point when the upper and lower split images meet, one above the other and the measuring points coincide.
| Measuring points|| |
a) For. Corneal thickness
i) Endothelium of upper segment.
ii) Epithelium of lower segment.
b) For Anterier chamber depth.
i) Epithelium of upper corneal segment.
ii) Anterior pole of lens in lower segment. (Corneal thickness first determined, then deducted)
c) For Antero-posterior axis of lens
(to be done under full mydriasis)
i) Posterior pole of upper lens segment.
ii) ii) Anterior pole of lower lens segment.
| Measuring the corneal thickness|| |
Ths split image is in two parts as two well focussed segments separated by a horizontal line. When the measuring scale is moved from zero, the lower image moves to the right of the observer. For correct corneal thickness measurement, the epithelial edge of the lower segment must coincide with the endothelial edge of upper segment. Their correct coincidence gives the thickness.
In each eye, corneal thickness was measured in the centre of cornea and its nasal and temporal periphery. To keep the distance form the nasal and temporal limbus constant, these readings were taken with a 5 mm slit beam, the upper and lower ends of the beam just touched the limbus above and below the horizontal line. This helped to keep the variation to its minimum. The centre of cornea was located by keeping the slit in such a way that it bisected the pupil vertically.
Three readings, are taken and the mean value is determined. Corresponding corrective value from the appropriate table is added to the mean value to obtain the final result in millimeters.
Patients attending the ophthalmic OPD of Gita Bhawan Hospital were selected for corneal pachometry. The only criterion was not to have a gross anterior segment disease. Refractive status was determined under appropriate mydriatic cycloplegic.
| Observations|| |
Keeping in mind the development of cornea, the clinical material has been divided into three age groups 10-19, 20-39 and 40 above as shown in the table below.
It is evident that there is good representation of the age group and both sexes.
Refractive state of each eye was determined and is given in the following table.
There were sixty emmetropic eyes and 170 myopic eyes. Of the myopic eyes 100 were high myopics above 6 Dioptres and 70 had small to moderate myopia of less than 6 Dioptres. The hypermetropic eyes, 10, did not include the aphakics.
[Table - 3] compares average corneal thickness in the three zones in males and females.
Peripheral thickness is distinctly less in females.
Measurements of corneal thickness in different refractive states are given in the following table.
It is evident that cornea is thinner in the centre than in the periphery, average being 0.623 mm. Itis also evident that cornea is thicker in the periphery and it is distinctly thicker in temporal than in nasal periphery.
| Discussion|| |
The reports in literature mainly indicate the measurements of the central cornea alone and do not give the measurements of peripheral cornea. The average thickness of central cornea reported from western countries by different authors varies between 0.507 mm to 0.523 mm.
Martola & Baum studied 209 normal eyes and have reported observations on central and peripheral corneal thickness. Their value for mean central thickness is 0.523 mm. The report does not give the exact values- for peripheral thickness but states that significant thinning of periphery with decrease in the ratio of peripheral to central thickness is evident after the age of 50 years. They have reported no difference in corneal thickness in different errors of refraction and sexes.
As against this, average thickness in central cornea in this series in 0.623 mm. It is further evident that cornea is thicker in temporal periphery than on the nasal periphery. Corneal periphery in females is distincty thinner compared to males although there is-practically no difference in central thickness. There is some change depending on refractive status but it is not very signigicant.
| References|| |
|1.||Martola, Eva-Lisa, Baum, J.L., 1968, Arch. Ophthalmol. 79: 28. |
[Table - 1], [Table - 2], [Table - 3], [Table - 4]