864 AMERICAN JOURNAL OF OPHTHALMOLOGY JUNE, 1969

8. Bettremieux, V. I. : A simple sclerotomy. Ann. Ocul. 139:385, 1908.

9. Dolganov, V. I. : Planing of the sciera and its evaluation as a new method of surgical treatment of glaucoma. Vrachebn. J. 1:4, 1922.

10. Krasnov, M. M. : Technique of sinusotomy and its variations. Vest. Oftal. 1968, No. 3, p. 31.

11. Forbes, M. : Gonioscopy with corneal inden­tion. Arch. Ophth. 76:488, 1966.

12. Harms, H. and Dannheim, R. : Results and problems of trabeculotomy. II Internat. Symposium microsurgery of eye. Bürgenstock, 1968, in print.

13. Rohen, J. : Morphology of the chamber angle tissue in normal and glaucomatous eyes. II Internat. Symposium microsurgery of eye. Bürgenstock, 1968, in print.

14. Strachan, I. M. : Discussion. II Internat. Symposium microsurgery of eye. Bürgenstock, 1968, in print.

15. Golovachev, Ju. V. : The condition of the an-

Tornquist1 showed that the radius of cur­vature of the cornea in eyes with acute glau­coma averaged 4% less than in normal eyes, and that the mean corneal radius of eyes with acute glaucoma was significantly less than that in normal eyes with equally shallow anterior chambers. Grieten and Weekers2

confirmed that the corneal radius of eyes with closed-angle glaucoma was less than that of normal eyes, and found that the mean corneal radius was less in the glaucomatous eyes than in normal eyes in persons of equal age and with similar hypermetropia.

Recently, I3·4 showed that the major ana­tomic factors determining the shallow ante­rior chambers in primary angle-closure glau­coma were faulty co-ordinations of the thickness and position of the lens in relation to axial length. Additionally, angle-closure glaucoma occurs mostly in eyes that are

This study was supported by Research Projects No. 14 of the Ophthalmic Research Institute of Australia and No. 13 of The Royal Victorian Eye and Ear Hospital, Melbourne.

terior chamber angle following surgery on Schlemm's canal in primary glaucoma. Vest. Oftal. 1968, No. 1, p. 21.

16. Smelowsky, A. S. : Sinusotomy : Its modifica­tion and possible combinations with other proce­dures. Vest. Oftal. 1967, No. 6, p. 31.

17. Khasanova, N. K., Kiselev, G. A. and Kolot-kova, A. J. : Results of sinusotomy and iridosclero-tomy after Pokrovsky. Vest. Oftal. 1968, No. 4, p. 32.

18. Harms, H. : Glaucoma operations and Schlemm's canal. Sitzungsbericht 114. Versamml. Vereins Rhein-Westf. Augenärtzte, 1966, v. 22.

19. Protopopov, B. V. and Kossovsky : Choice of operations in glaucoma. Tr. I l l Ophth. Cong. USSR, Volgograd, 1966, p. 198.

20. Kiselev, G. A. : Hydrodynamic changes in the eye in pathogenetically oriented surgical manage­ment of glaucoma. Tr. I l l Ophth. Cong. USSR, Volgograd, 1966, p. 280.

shorter than average, although it can occur in eyes of any axial length.

The present paper determines the signifi­cance of correlations between radius of cor­neal curvature and other measurements in normal eyes and in those with primary an­gle-closure glaucoma.

TECHNIQUE AND PATIENTS

The radii of corneal curvature were mea­sured in the two principal meridians with a Javal-Schi^tz keratometer (Haag-Streit). The mean of the two measurements was used in the calculations. Anterior-chamber depths were measured with the two attach­ments for the Haag-Streit 900 slitlamp5 and included corrections for corneal curvature. With 15 megacycles/second time-amplitude ultrasonography using a stand-off technique, the following measurements were deter­mined: corneal thickness, lens position and axial length. The validity of this method has been previously reported.3

The patients were the same as those used

CORNEAL RADIUS AND OCULAR CORRELATIONS IN NORMAL EYES AND EYES WITH PRIMARY ANGLE-CLOSURE GLAUCOMA

RONALD F. LOWE, M.D. Melbourne, Australia

VOL. 67, NO. 6 C O R N E A L R A D I U S A N D OCULAR C O R R E L A T I O N S 865

in the lens-correlation studies,4 except that one of the eyes with angle-closure glaucoma gave rough keratometer readings thereby re­ducing the glaucoma eyes from 118 to 117.

COMPARISON OF CORNEAL RADII

The radii of corneal curvature of normal and angle-closure glaucoma eyes are com­pared in Table 1. Although there is consider­able overlap, the mean corneal radius of an­gle-closure glaucoma eyes is significantly less than for normal eyes. In this series, the difference between the mean of the two groups (0.06 mm) is considerably less than that found by Tornquist1 (0.25 mm) and by Grieten and Weekers2 (0.20 mm).

CORNEAL RADIUS COMPARED WITH AXIAL LENGTH

The mean radius of corneal curvature was compared with axial length in each eye. The radius of corneal curvature is significantly correlated with axial length for both normal and angle-closure glaucoma eyes (table 2).

Tornquist1 found that the cornea in acute glaucoma averaged 4% smaller than in nor­mal eyes, and my ultrasonic measurements4

showed that the axial lengths of angle-clo­sure glaucoma eyes averaged 5% less than in normal eyes.

In both types of eyes, small corneas are generally associated with small eyes, and as the average angle-closure glaucoma eyes have shorter axial lengths than normal eyes, and as corneal radius is correlated with axial

TABLE 1 COMPARISON OF MEAN RADIUS OF CORNEAL

CURVATURE OF NORMAL AND ANGLE-CLOSURE GLAUCOMA EYES

Statistics

No. of eyes Mean corneal

radius Standard

deviation Standard error

of mean Range

t—test on means Significance

Normal Eyes

157 7.67 mm

0.24

0.019

7.13-8.54 mm

Angle-Closure Glaucoma

Eyes

117 7.61 mm

0.29

0.027

6.96-8.31 mm

t = 2.049, d. of f. = 272 0 . 0 5 > P > 0 . 0 2 , significant

length, the smaller corneal radius in angle-closure glaucoma compared with normal eyes appears to be an expression of the slightly smaller size of most angle-closure glaucoma eyes.

The angle-closure glaucoma cornea, de­spite its slight but significant reduction in mean radius of curvature, remains a nor­mally co-ordinated structure in relation to axial length. The normality of the cornea is stressed by comparison with the lens where deviations from normal correlations produce the characteristic shallowness of the anterior chamber of primary angle-closure glau­coma.4

CORNEAL RADIUS AND LENS THICKNESS

Mean radius of corneal curvature was compared with lens thickness of the same

TABLE 2 STATISTICS OF MEAN RADIUS OF CORNEAL CURVATURE (X) V ULTRASONIC AXIAL

LENGTH (Y) OF NORMAL AND ANGLE-CLOSURE GLAUCOMA EYES

Statistics

No. of eyes Regression line Standard error of regression variance Due to regression variance About regression variance F —ratio Significance Correlation coefficient Significance

Normal Eyes

157 Y = 11.32 + 1 .54X

0.24 21.28

0.54 39.73

Extremely, P < 0 . 0 0 0 5 +0 .452

highly, P < 0 . 0 0 1

Angle-Closure Glaucoma Eyes

117 Y = 5 . 7 8 + 2 . 1 4 X

0.26 46.10

0.67 66.22

Extremely, P<0 .0005 + 0 . 6 0 5

highly, P < 0 . 0 0 1

866 AMERICAN JOURNAL OF OPHTHALMOLOGY JUNE, 1969

TABLE 3 STATISTICS OF MEAN RADIUS OF CORNEAL CURVATURE (X) V ULTRASONIC LENS

THICKNESS (Y) OF NORMAL AND ANGLE-CLOSURE GLAUCOMA EYES

Statistics

No. eyes Regression line Standard error of regression coefficient Due to regression variance About regression variance F—ratio Significance Correlation coefficient Significance

Normal Eyes

157 Y = 6 . 3 4 - 0 . 2 4 X

0.111 0.515 0.111 4.645

0.05 > P > 0.025 Significant - 0 . 1 7 1

0 . 0 5 > P > 0 . 0 2 5 Significant

Angle-Closure Glaucoma Eyes

117 Y = 4 .75+0 .051 X

0.128 0.026 0.166 0.158

Not significant +0 .037

Not significant

normal and angle-closure glaucoma eyes (table 3) . In normal eyes, radius of corneal curvature is significantly correlated with lens thickness. Both measurements are correlated with axial length.

In primary angle-closure glaucoma eyes no correlation was found between corneal radius and lens thickness. These findings ac­cord with the correlation of corneal radius with axial length and the absence of correla­tion between lens thickness and axial length in these eyes.4 These results provide further evidence of the disturbance of co-ordination of the lens with the eyeball in primary an­gle-closure glaucoma.

COMPARISON OF AGE WITH CORNEAL RADIUS

The mean radius of corneal curvature for normal and angle-closure glaucoma eyes was analyzed statistically with respect to age (table 4) . All persons were aged at least 30 years.

The regression lines are practically flat for both types of eyes and no correlation could be found between corneal radius of curvature and age. Previously, no correlation was found between axial length and age.4

Both normal and primary angle-closure glau­coma eyeballs appear to undergo no signifi­cant change in size with age when measured by the techniques described in these papers. (Radius of corneal curvature and axial length are used as parameters of eyeball size.)

By contrast, marked changes occur in the lens with age.4 Increase of lens size with age may, at times, have a significant effect for angle-closure glaucoma by producing in­creased shallowness of an already shallow anterior chamber,4 but age appears to have no effect in angle-closure glaucoma as far as the curvature of the cornea or the axial length are concerned.

CORNEAL RADIUS AND ANTERIOR-CHAMBER DEPTH

Radius of corneal curvature was com­pared with anterior-chamber depth (table 5). The optical measurements of anterior-cham­ber depth by the Haag-Streit apparatus ex­tend to two decimal places so were preferred to the ultrasonic measurements which extend to only one decimal place.

No correlation was found between radius of corneal curvature and anterior-chamber depth for normal and angle-closure glau­coma eyes. A negative correlation might be expected if other factors remained un­changed because height of cornea could in­crease as the radius of cornea diminished7

but increased corneal radius is likely to be associated with a smaller eyeball and a smaller cornea. Further, as there is a posi­tive correlation between lens position and axial length,4 the relatively forward lens in smaller eyes would lead to a shallowing of the anterior chamber that would probably neutralize any deepening caused by increased

VOL. 67, NO. 6 CORNEAL RADIUS AND OCULAR CORRELATIONS 867

TABLE 4 STATISTICS OF AGE (X) V MEAN RADIUS OF CORNEAL CURVATURE (Y) OF

NORMAL AND ANGLE-CLOSURE GLAUCOMA EYES

Statistics

No. of eyes Age range Regression line Standard error of regression coefficient Due to regression variance About regression variance F—ratio Significance Correlation coefficient Significance

Normal Eyes

157 30-85 yr

Y = 7.70-0.0005X 0.0014 0.00582 0.0582 0.100

Not significant - 0 . 0 2 5

Not significant

Angle-Closure Glaucoma Eyes

117 36 to 84 yr

Y=7 .62 -0 .0002X 0.0024 0.000352 0.0878 0.0040

Not significant - 0 . 0 0 5 9

Not significant

corneal curvature. Stenstrom7 found no correlation between corneal radius and ante­rior-chamber depth for normal eyes but, if eyes were selected for a constant axial length (and presumably for similar corneal curva­ture), a negative correlation could be shown between corneal curvature and anterior-chamber depth.

Differences in radius of corneal curvature appear to be of no significance for anterior-chamber depth in primary angle-closure glaucoma.

CONCLUSIONS

The means of the radii of corneal curva­ture of normal and primary angle-closure glaucoma eyes show a small but significant difference. Radius of corneal curvature is correlated with axial length and lens thick­ness for normal eyes, and with axial length

,f or angle-closure glaucoma eyes ; but corneal radius is not correlated with lens thickness in angle-closure glaucoma, nor with anterior-chamber depth in either series of eyes.

The slightly smaller mean radius of cor­neal curvature in primary angle-closure glaucoma appears to be an expression of smaller mean eye size (also shown by com­parably shorter axial length), but this seems to be of no significance in relation to the de­velopment of primary angle-closure glau­coma.

The cornea appears to be a co-ordinated structure in both types of eyes. In normal eyes, the position and thickness of the lens is co-ordinated with axial length and corneal curvature.* In angle-closure glaucoma eyes, it is the lack of co-ordination of position and thickness of the lens with respect to corneal

TABLE 5 STATISTICS OF MEAN RADIUS OF CORNEAL CURVATURE (X) V OPTICAL ANTERIOR

CHAMBER DEPTH ( Y ) OF NORMAL AND ANGLE-CLOSURE GLAUCOMA EYES

Statistics

No. of eyes Regression line Standard error of regression coefficient Due to regression variance About regression variance F-ratio Significance Correlation coefficient Significance

Normal Eyes

157 Y = 2 . 3 9 + 0 . 0 4 4 X

0.114 0.0173 0.117 0.148

Not significant +0 .0309

Not significant

Angle-Closure Glaucoma Eyes

117 Y = 2.16-0.042X

0.080 0.018 0.065 0.278

Not significant - 0 . 0 4 9 1

Not significant

868 AMERICAN JOURNAL OF OPHTHALMOLOGY JUNE, 1969

curvature and axial length (eyeball size) which causes the shallow anterior chamber that predisposes the eyes to angle-closure glaucoma.4

Emmetropia is excessively prevalent in the general population compared with re­fractive errors. This is because the refrac­tive power of the lens is co-ordinated with axial length and corneal refraction8 (radius of corneal curvature). Many simple refrac­tive errors can be considered the result of failure of lens co-ordination.

Likewise, it is a failure of co-ordination of lens position and thickness in relation to normal eye shape (corneal radius and axial length) which leads to the unduly shallow anterior chamber that provides the anatomic basis for primary angle-closure glaucoma.

SUMMARY

The mean radius of corneal curvature for a series of primary angle-closure eyes is slightly, but significantly, less than for a se­ries of normal eyes. Radius of corneal cur­vature is significantly correlated with axial length in normal and primary angle-closure glaucoma eyes. The smaller radius of curva­ture of the cornea is of no importance in producing the anatomic factors underlying primary angle-closure glaucoma, but it is considered to be an expression of the smaller mean size of the glaucoma eyes. Corneal ra­dius of curvature does not change signifi­cantly after the age of 30 years. Unlike the lens, the cornea appears to be a co-ordinated

structure in primary angle-closure glaucoma eyes.

82 Collins Street (3000)

ACKNOWLEDGMENTS These investigations were conducted in the Glau­

coma Unit of The Royal Victorian Eye and Ear Hospital. The ultrasonographic equipment and a grant for expenses were received from the Ophthalmic Research Institute of Australia. I thank my hospital colleagues for permission to ex­amine patients and for access to records. Dr. Magda Horvat rendered valuable clinical assistance, took the keratometer measurements and was my as­sociate with the ultrasonography. Mr. K. Shankly, M.Sc, analysed the statistics with the computer in the Biophysics Section of the Department of Physi­ology of the University of Melbourne.

REFERENCES

1. Tornquist, R. : Corneal radius in primary acute glaucoma Brit. J. Ophth. 41:421, 1957.

2. Grieten, J. and Weekers, R. : Etude des dimen­sions de la chambre antérieure de l'oeil humain, 3* partie. Ophthalmologica 143 :409, 1962.

3. Lowe, R. F. : Time-amplitude ultrasonography for ocular biometry. Am. J. Ophth. 66 :913, 1968.

4. : Causes of shallow anterior chamber in primary angle-closure glaucoma : Ultrasonic biome­try of normal and angle-closure glaucoma eyes. Am. J. Ophth. 67:87, 1969.

5. : New instruments for measuring ante­rior chamber depth and corneal thickness. Am. J. Ophth. 62:7, 1966.

6. : Linear A-scan ultrasonography in measurements of intraocular distances. Tr. Ophth. Soc. Aust. 26 :72, 1967.

7. Stenstrom, S. : Variation and correlations of the optical components of the eye. In Modern Trends in Ophthalmology. (Sorsby, A. ed.) Lon­don, Butterworth, 1948, v. 2, p. 94.

8. Franceschetti, A. and Gernet, H. : Importance of ultrasonic echography for measurements of the optical components of the eye. Tr. Am. Acad. Ophth. Otolaryng. 69 :46S, 1965.