ACTA OPHTHALMOLOGICA VOL. 38 1960

From the Eye Clinic of the University Central Hospital, Helsinki (Head: Professor M . Vannas, M. D.)

ON THE REFRACTIVE POWER OF THE

CORNEA AND EMBRYONTOXON CORNEAE POSTERIIJS IN HIGH DEGREES OF HYPERMETROPIA")

BY

Henr ik Forsius

In this paper, + 5 d or more of hypermetropia is termed high. In Finland the incidence of such hypermetropias has been calculated at 0.9 per cent on the basis of a practitioner's patients aged 10 - 70 years (Heinonen). The data con- cerning the incidence vary in the reports of different authors from different countries. Among 5086 young men of military age Stromberg, in Sweden, found only 0.338 per cent eyes with over 5 d of hypermetropia, whilst Kron- feld & Dewney in a series of private patients encompassing 2229 eyes found 1.53 per cent such eyes after administration of atropine (Table 1). Broekema, who recorded the occurrence of hypermetropia of 1 - 16 d in a series of out- patients visiting a Dutch university clinic, reported that among 2350 eyes, 20.9 per cent of those showing hypermetropia had this error in a high degree. In a series of German outpatients who had sought medical aid on account of errors of refraction, Betsch observed hypermetropia in 0.93 per cent of 12,000 eyes. Stenstrijm stated that ametropia is commoner in women than in men.

Visual acuity decreases with increasing hypermetropia. In part, at least, this is due to insufficient exercise of the retinal function, since in children sight is often improved after glass correction (Duke-Elder). According to Broekema, vision was normal (1.0) in 44.4 per cent of 277 eyes with 5 - 6 d of hyper- metropia against 15.1 per cent in 86 eyes with 7 - I0 d. Those with an error of 1 - 2 d had normal acuity in 82 per cent of cases (Table 2).

Subjects with high hypermetropia frequently also exhibit marked astigma- tism. In the tables published by Leibovics in his study concerning astigmatism it appears that of 223 subjects with a refraction above 5 d, 15.2 per cent were astigmatic by 2 d or more, whilst of 3333 subjects with a refraction between plus and minus 1, 8.8 per cent showed astigmatism of this order.

") Received Sept. 24th 1959.

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Table 1. Occurrence of different degrees of hypermetropia expressed as percentages according

to different authors. I I I

Heinonen Stromberg Kronf eld & Dewney

No. -+ 1 2229 I 4975 1 5086

f l + 2

+ 3 + 4

+ 5 $ 6

+ 7 + 8

38.12 23.99 12.69 } 36'9 1.69

4.68 1.44

0.855 0.45

3.1

0.6

0.18 0.045 ] 0.3

0.39 0.22

0.18 0.079

0.079 0.02

> 5 1.53 OIo 0.9 010 0.338 O/o

Table 2. Visual acuity in hypermetropia according to Broekema.

Visual acuity 1 3 14 1 /2 1 /3 114 116

+ l , +2 82 O / o 10 @/o 5 O / o 1.8 O / o 0.4*/0 0.8 O / o

Dgree of +3, +4 61.5 O/o 15.1 O / o 13.9 O / o 3.9 O / o 2.5O/o 1.1 O / o

hypermetropia 4-5, +6 44.4 O / o 23.5 OIo 17.7 O / o 7.2 * l o 4.3"lo 2.9 O / o

+7-+10 15.1 O / o 18.8 "10 44.4 O/o 11.6 O / o 5.S0/0 4.6"/0

Theoretically, high hypermetropia may be due to reduced refractive power of the cornea, to a low effective refractivity of the lens, a small axial length of the eye, or a low refractive index of the refractive media. The cause may also be a combination of these factors. In his fundamental work on the develop- ment of the refractive conditions Steiger stated that the distribution of the refraction is explicable on the basis of a free variation of the optical com- ponents, and that hypermetropia is thus the result of an unfavourable com- bination of globe length and refractive power of the cornea. Later, Tron, Stenstrom and Sorsby et al. have shown that the refractive power of the lens and the depth of the anterior chamber also play a part. The same authors also demonstrated the presence of certain correlations between, for instance, the

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length of the eye and the radius of the cornea. On the basis of these correlations Sorsby et al. were able to explain the distribution of the refraction in all ametropias between plus and minus 4. The correlation between the refractive power of the cornea and the length of the eye decreases with increasing hyper- metropia, and in hypermetropia of + 8 d there is no correlation a t all. I n these cases the axial length is the decisive factor. The above-mentioned authors showed that out of 20 eyes with + 4 d or more of hypermetropia, 19 had an axial length of less than 23 mm., and that all investigated eyes with + 8 d had an axial length of less than 22 mm. They reported that the mean length of the emmetropic eye is 23.85 mm. Stenstrcm noted a linear correlation between the length of the eye and the radius of the cornea throughout the whole range of refraction, but he emphasized that his material was too scanty to allow of any definite conclusions in respect to the high degrees of hyper- metropia. Hypermetropes over + 8 d all had an abnormally short eye.

As a rule, the refractive power of the cornea is expressed in dioptres and not as radial length of the cornea, although the latter value is exact and the

dioptre value is calculated by the formula d = __ r . On Haag-Streit’s corneal n - 1

refractometer, which was used in the present investigation, n = 1.3375 and a radius of 7.5 mm. corresponds to 45 d.

Normally, the refractive power of the cornea varies between 40 and 47 d. In a Finnish series, Heinonen noted a mean value of 43.57 d in 3099 eyes, and similar results have been reported from other countries. As mentioned in the foregoing, the cornea plays a minor part in the development of high ametropia. Steiger reported mean values of 43.63 in 300 emmetropes, 43.12 in 141 children of school age who had over + 4 of hypermetropia, and 44.14 d in 1 7 1 myopes with over 6 d. Thus, the cornea is responsible for one-eighth of the ametropia, at the utmost. Whilst the graphic curve for the emmetropic eye is gaussian, the curves for ametropes are uneven. According to Steiger, a >>disturbance of the structural harmony<< is involved.

After Steiger, other authors, too, have demonstrated a weak negative correla- tion between the corneal and the total refraction (Czellitzer, Stenstrom).

A greyish prominence of the papilla called pseudo-papillitis has been linked with hypermetropia since 1881, when Dobrawolsky saw this phenomenon in a 5-year-old girl. Nottbeck described 20 cases of pseudo-papillitis, 6 of which ex- hibited 5 d or more of hypermetropia. The frequency of pseudo-papillitis re- ported by different authors varies depending on the diagnostic criteria adopted.

According to Sugar, hypermetropic eyes are predisposed to closed-angle glaucoma. Of 140 patients with acute glaucoma, only 7 were myopes, and the hypermetropes had an average hypcrmetropic refraction of + 2.72 d. Hyper- metropes have a shallow anterior chamber, which increases the risk of closure

1000 __

of the chamber angle. Stenstrom observed a decrease in depth of the chamber until 2 - 3 d of hypermetropia, after which the chamber depth increased with increasing degree of the error.

In moderate hypermetropia convergent strabismus often develops as a result of a disturbance of the relationship between accommodation and convergence. Scobee stated that in high hypermetropia, where the need for accommodation exceeds the normal physiological limits, convergent strabismus is a less common accompaniment than in low hypermetropia. Broekema reported squint in 11 per cent of hypermetropes with isometropia against 16.5 per cent in the aniso- metropes of his series. The frequency of squint is highest until 2 d, decreases between 2 and 7 d, and occurs sporadically in the highest degrees of hyper- metropia. In Broekema’s series, divergent strabismus was observed in three cases in connection with anisometropia and in one case in connection with isometropia. By contrast, 159 subjects showed convergent strabismus.

As a rule, the anterior border-ring of Schwalbe is only visible on gonioscopic examination, but Burian et al. stated that in 15 per cent of all eyes it is visible biomicroscopically as a glassy-appearing membrane, which is mostly seen only in the lateral and medial part of the limbus. Frequently other signs of meso- dermal dysgenesis, such as hypoplasia of the iris, are also present. In cornea plana, which is a hereditary malformation involving a large corneal radius and mostly high hypermetropia, this embryontoxon corneae posterius (Axenfeld) is often seen. The occurrence in other kinds of high hypermetropia has not been studied.

O W N INVESTIGATIONS

The ocular examination involved determination of the visual acuity and the radius of the cornea. Furthermore, the presence of embryontoxon corneae posterius, malformations of the iris, glaucoma and pseudo-papillitis was re- corded. The patients with glaucoma and some patients of presbyopic age ex- cepted, the refraction was in all cases determined with mydriatics. The corneal refractometer (Haag-Streit’s new model) was adjusted using a control ball. The values recorded apply to the axis nearest to the horizontal plane. The series consisted to 60 per cent of patients from the outpatients’ department of the Eye Hospital, to 40 per cent of private patients of the author’s. Obviously microphthalmic eyes and cases of cornea plana were not included, nor cases of acquired hypermetropia such as aphakia.

The age of the patients varied between 4 and 69 years, the mean age being 25.5 years. The control series consisted of 57 of the author’s private patients who had a refraction between plus and minus 3. Their mean age was 25.1 years (range from 7 to 52 years).

The series of hypermetropes consisted of 122 eyes with 4- 5 d or more,

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belonging to 67 subjects. Of these, 45 were women and 32 were men. Hyper- metropia of 7 d or more was noted in 54 eyes, 32 of which belonged to men.

The distribution of the total material was as follows:

Degree of hypermetropia + 5 +6 + 7 +8 +9 4-10 +11 +12 No. of cases 34 34 33 13 5 2 0 1

Since vision could not be determined in the three youngest patients, visual acuity was determined in a total of 116 eyes. The mean value was 0.59. In 39 per cent of the eyes investigated the acuity was 0.8 or more. When different values were obtained a t repeated examinations, the highest value was taken into account. When those eyes were excluded where sight was impaired on account of squint, glaucoma or any other demonstrable disease, 98 eyes re- mained. The visual acuity (Table 3 and 4) was largely the same in the dif- ferent degrees of hypermetropia, i. e. 0.73 on average, and 0.8 or more in 46 per cent.

In the control series the visual acuity was 1.1 on average and 0.8 or more in 91 per cent of eyes.

Astigmatism is not taken into account in the values for hypermetropia re- corded. A refraction of + 5 s c y l . + 3, for instance, was recorded as + 5 d. Astigmatism was present in 9 eyes to a degree of 2 d or more. In all cases it was of the type termed direct or >,with the rule..

In the present series the mean value for the refractive power of the cornea was 42.4 dioptres. The corresponding value for a normal series consisting of 315 eyes was 43.50. The difference is highly significant (P = 0.001). This difference represents, however, only a small proportion of the difference in refraction between the two series. Hence, it may be concluded that the cornea played only a minor part in the development of the hypermetropia. The pathological features of the hypermetropic eyes are obvious if the distribu-

Table 3. Visual acuity in high hypermetropia. Out of 98 eyes 46 per cent had an acuity of 0.8

or less, the mean value being 0.73.

Degree of hypermetropia

Visual acuity

< + 6 < + 7 < + 8 < + 9 < + 10 < + 11

0.81 0.61 0.64 0.69 0.8 0.65

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Table 4 . Vision in 98 eyes without amblyopia due to squint, glaucoma, etc.

D e g r ~ e OJ hypermetropie

Table 5. Refractive power of the cornea in dioptres.

cases 2 +5 94 94

tion over different dioptre values is analysed (Table 5 , Fig. 1 ) . The curve for the normal series is even, and the dispersion is smaller than in the pathological series, although the latter consists of a smaller number of patients. The eyes showing hypermetropia over 7 d seemed to have a larger corneal radius than

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315 norm. +5++/2D _ _ _ n -15-

4 I \ I t

-20 ',

\ - ' L U O ' L ~ / ' I L . Z ( 2 ~ C 4 3 I < P 4 1 1 ~ 4 5 I - c U b Id47 I-=:

Rejracti've power ofthe cornea in dtopkm

Fig. 1. Refractive power of the cornea in dioptres expressed as percentages

those with lower hypermetropia, but the difference between these two groups - those over and those under 7 d - is not significant on this point.

Embryontoxon corneae posterius was observed in 29 eyes out of 116 in- vestigated. Only those cases were included where the anterior border-ring of Schwalbe was biomicroscopically visible and clearly prominent a t least a t one point. The distribution over the different degrees of hypermetropia appears in Table 6. Of the 114 normal eyes 14 showed this anomaly of the cornea. The difference is significant (P = 0.05).

Table 6 . Occurrence of embryontoxon corneae posterius in different degrees of hypermetropia.

Degree cf byperme fropia

Tnble 7. Changes of the iris in high hypermetropia. Out of 109 eyes, 29 showed persistent

pupillary membrane or hypoplasia of the iris.

The iris was investigated in 109 eyes. Persistent pupillary membrane in the form of threads over the pupillary area or hypoplasia of the iris was observed in 29 cases against 9 in the normal series. The difference is statistically highly significant (P = 0.001). For details, see Table 7 .

Anisometropia of 2.5 - 7.25 d was present in 9 cases. In these, the refraction of one eye was under + 5 d, the mean being 2.23 d, whilst the mean refraction of the other eye was + 6.66 d. Among the eyes showing the slighter error of refraction there was one with enibryontoxon corneae posterius against 4 in the group with the greater error. Persistent pupillary membrane was seen in 4 and 5 cases, respectively, in the two groups. The radius of the cornea was almost exactly the same in the groups of eyes, i. e. 42.0 and 41.9 d, respectively, and showed very little variation within the individual pairs of eyes, the difference being more than one dioptre in one case only. Hence, it may be concluded that the cornea was not responsible for the anisometropia. Three of the 9 patients under discussion squinted.

Glaucoma was present in 7 eyes of 4 patients, all of whom were over 30 years old. This age group comprised 26 subjects. One patient had a wide chamber angle and a diagnosis of glaucoma simplex, whilst the remainder had a narrow chamber angle and suffered from closed-angle glaucoma, with the exception, perhaps, of one case where the diagnosis was uncertain. The development of

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the disease was probably in part due to a shallow chamber, which is charac- teristic of hypermetropia. In none of these cases was the anterior border-ring of Schwalbe visible biomicroscopically, and the radius of the cornea cor- responded to 45.17 d. One patient, a 33-year-old woman, had hypermetropia of + 8 on the right eye and + 9 on the left. I n this case the dioptre value for the cornea was 48.75 d, which was the highest in the whole series. Since the diameter of the cornea and the breadth of the eye were normal, it is obvious that the eye was markedly flattened posteriorly. On examination, it did not appear to be microphthalniic.

Squint was strikingly frequent, being observed in 26 subjects out of 56. One patient who had anisometropia had divergent strabismus, whilst the remainder had convergent strabismus. Squint was equally common in those cases where the less hypermetropic eye was under 7 dioptres as in the patients exhibiting hypermetropia over 7 d.

Table 8.

Degree of hypermetropia t 5 +6 $ 7 +8 4-9 4-10 No. of cases 20 15 13 6 1 1 No. of patients with strabismus 7 9 7 2 1 0

True pseudo-papillitis was observed only in 2 eyes out of 102 investigated. In addition, the optic disc had somewhat diffuse margins in 12 cases. Nine eyes showed less than 7 d of hypermetropia, and 5 eyes showed hypermetropia of more than 7 d. In the normal series, the optic disc had somewhat diffuse margins in 6 out of 114 eyes. The difference between the hypermetropic and the normal series is insignificant on this point.

The series encompassed one case of heredodegeneration of the retina, one case of slight rotator nystagmus, one spastic patient and one case of mental debility where the limbus corneae was hazy owing to extension of the corneo- scleral junction far over the cornea, as is also seen in cornea plana.

DISCUSS10 N A N D CONCLUSlO NS

The various factors investigated show a relatively even distribution over the series. Pathological findings are lacking only in a small proportion of cases. If those showing strabismus, embryontoxon corneae posterius, changes of the iris, diffuse margins of the optic disc and a visual acuity under 0.8 are omitted, there remain only 16 eyes, or 13.1 per cent against 71.8 per cent in the normal series.

In the series with hypermetropia, vision was markedly lower than in the control series, but it was approximately the same in the different degrees of

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hypermetropia. Steiger showed that hypermetropic eyes have a somewhat larger corneal radius than normal eyes. In the higher degrees of hypermetropia a tendency in this direction is revealed by the tables published by Stenstrom and by Sorsby et al. In the present series, which encompassed a relatively large number of extreme hypermetropias, the difference between these and the normal series was found to be highly significant.

The frequent occurrence of minor malformations of the cornea and the iris seems to be indicative of a developmental disturbance of the eye, most probably of the mcsoderm, of which the sclera, the cornea and the iris are formed. That an anomaly of the sclera is involved appears from the fact that high hyper- metropia as a rule is due to shortness of the axis of the eye (Tron, Stenstrom, Sorsby et al.).

The number of patients showing strabismus was strikingly large as compared with Broekema’s series from 1909, which also was collected from the out- patients’ department of a university clinic.

Summing up, a markedly hypermetropic eye is mostly deficient in several respects.

SUMMARY

The material consisted of 122 cases of hyperopia of 5 d or more of which 54 were + 7 d or more hyperopic. 39 per cent of the patients had vision of 0.8 or more; the average was 0.59. The refractive power of the cornea averaged 42.4 against 43.50 d in the control material (315 cases). The difference is significant. P = 0.001.

29 of 116 eyes had embryontoxon corneae posterius (visible anterior border- ring of Schwalbe), while the corresponding ratio for the control material was 14/114. P = 0.05. Hypoplasia of the iris or persistent pupillary membrane were seen in 29 out of 109 eyes against 9 out of 114 in the control materia1.P = 0.001. Glaucoma simplex was established in one case and three others had closed angle glaucoma.

26 of 56 patients squinted. Strabismus occurred in 46 per cent of the cases with less than 7 d and in 48 per cent of the cases with 7 d or more.

Pseudopapillitis was established in 14 out of 102 cases against 6/114 in the control group.

Anisometropia of 2.5 - 7.25 was present in 9 cases. The radius of the cornea was almost exactly the same in the two groups of eyes.

R E F E R E N C E S

Betsch A,: Klin. Mbl. Augenhk. 82: 365: 1929. Broekema /. C.: Bijdrage tot de Kennis der Hypermetropie. Diss. 1909. s-Gravenhage.

-F. Mol. Amsterdam.

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Bzuian H. v. , Braley A . E. & Allen L.: Arch. Ophth. 53: 767: 1953. Czellitzer: Cit. Stenstrom. Dobruwolsky: Cit. Nottbeck. Duke-Elder S.: Text-book of Ophthalmology Part IV, 4276. H. Kimpton, London 1949 Heinonen 0.: Finska Lak. Sallsk. Hand]. 65: 172: 1929. Kronfeld P. C. &. Dewney C.: Graefes Arch. Ophth. 126: 487: 1931. Leibovics M.: Zeitschr. Ophth. Opt. 16: 33: 1928. Nottbeck B.: Graefes Arch. Ophth. 4 4 : 31: 1897. Scobee R. G.: The oculorotary mcsclcs. C. V. Mosby Co. St. Louis 19.52. Sorsby A., Benjamin B., Davey 1. l?.. Sheridun M. & Tanner /. M.: Emmetropia and

Steiger A,: Die Entstehung der spharischen Refraktion des menschlichen Auges.

Stenstrom S.: Acta Ophth. Suppl. 26: 1946. Stromberg E.: Acta Ophth. 14: 251: 1936. Sugar H . S.: The Glaucomas. P. B. Hoeber. 1957. Tron E.: Graefes Arch. Ophth. 132: 182. 1934.

its aberrations. Medical Research Council. Spec. Rep. 293. London 1957.

S. Karger. Stuttgart 1913.

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